Progressive Crop Consultant - September/October 2020

September / October 2020 How Citrus Pests Develop Resistance to Insecticides Argentine Ant Biology and Management in Citrus Research and Extension for California Cannabis Production The Art of Fertilization: Making Decisions on Nutrition

September 17-18, 2020 see more info on pages 46-47

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Volume 5: Issue 5

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PUBLISHER: Jason Scott Email: jason@jcsmarketinginc.com EDITOR: Marni Katz ASSOCIATE EDITOR: Cecilia Parsons Email: article@jcsmarketinginc.com PRODUCTION: design@jcsmarketinginc.com Phone: 559.352.4456 Fax: 559.472.3113 Web: www.progressivecrop.com

IN THIS ISSUE

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How Citrus Pests Develop Resistance to Insecticides

8

Argentine Ant Biology and Management in Citrus

14

CONTRIBUTING WRITERS & INDUSTRY SUPPORT

16

The Art of Fertilization: Making Decisions on Nutrition

18

Soil Health Field Trials at West Hills College Coalinga

24

Steven A. Fennimore

Research and Extension for California Cannabis Production

UCCE Extension Specialist, UC Davis

Luca Brillante

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Assistant Professor, CSU Fresno

Tim Ellsworth, Ph.D.

Ag Science Instructor, West Hills College Coalinga

Beth Grafton-Cardwell, Ph.D. UC Riverside, Director of Lindcove Research and Extension Center

Mark S. Hoddle

Extension Specialist in Biological Control, UC Riverside

Results of 2020 Kern County Potato Variety Trial

Craig Macmillan, Ph.D. Macmillan Ag Consulting, Kris Beal, M.S.,Vineyard Team

V I N E YA R D R E V I E W

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UCCE Entomology and Biologicals Advisor, San Luis Obispo and Santa Barbara Counties

Kevin Day

32

Autonomous Predictions of Vineyard Yield

38

Chemical and Biological Control of Nematodes Affecting Grapes in the San Joaquin Valley

42

Grape Berry Ripening and Preharvest Management

WRCCA Board of Directors

Jaspreet Sidhu

UCCE Staff Research Associate, Kern County, Jed DuBose, UCCE Vegetable Crops Farm Advisor, Kern County

Gabriel Torres

UCCE Farm Advisor, Tulare County, Elizabeth Fichtner, UCCE Farm Advisor, Tulare County

Houston Wilson

Asst. Cooperative Extension Specialist, UC Riverside

George Zhuang

UCCE Viticulture Farm Advisor, Fresno County

UC COOPERATIVE EXTENSION ADVISORY BOARD Surendra Dara

Control Strategies for Mealybug Pests and Vectored Viruses in Vineyards

Fred Strauss

Steven Koike Tri-Cal Diagnostics

Jhalendra Rijal UCCE Integrated Pest Management Advisor, Stanislaus County

UCCE Pomology Farm Advisor, Tulare and Kings Counties Kris Tollerup UCCE Integrated Pest Management Advisor, Fresno, CA Elizabeth Fichtner UCCE Farm Advisor, Mohammad Yaghmour Tulare County UCCE Area Orchard Systems Advisor, Kern County Katherine Jarvis-Shean UCCE Orchard Systems Advisor, Sacramento, Solano and Yolo Counties

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The articles, research, industry updates, company profiles, and advertisements in this publication are the professional opinions of writers and advertisers. Progressive Crop Consultant does not assume any responsibility for the opinions given in the publication.

September / October 2020

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How Citrus Pests Develop Resistance to Insecticides

By BETH GRAFTON-CARDWELL, PH.D.| UC Riverside, Director of Lindcove Research and Extension Center Citrus pests develop resistance to insecticides through a number of adaptions and natural traits.

I

n talking about insecticide resistance, we need to think in terms of populations of insects. Resistance occurs when some of the individuals in the population become less susceptible to an insecticide. When that insecticide is sprayed again, the resistant ones survive to reproduce, and if that insecticide continues to be sprayed, the population gradually becomes dominated by resistant individuals. These genes for resistance are passed on to their offspring.

The term tolerance is sometimes used; however, tolerance is the natural ability of an organism to withstand an insecticide. For example, green lacewings are naturally tolerant of pyrethroids because they have really high levels of esterase enzymes in their bodies. They didn’t develop resistance, they simply, naturally, tolerate the insecticide.

Insects Develop Resistance

There are four basic ways that insects develop resistance: 1. They are selected for behaviors that avoid the insecticide.

2. They change their cuticle so the pesticide cannot penetrate as easily.

3. They increase the number of enzymes they have to detoxify the pesticide and maintain normal function.

4. They change the nature of the target site so that the pesticide cannot bind to it.

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An example of a change in behavior is mosquitoes normally land on walls, and so spraying an insecticide on the wall will kill them. In a population, you have variability in behavior; some mosquitoes are prone to landing and some not. Over time and with successive sprays, the ‘landers’ are killed and the population is gradually selected so that it consists of mosquitos that hover and don’t land.

Many insecticides attack the nervous system of insects. Normally, a nerve impulse travels down the nerve and when it reaches a synapse (a break in the physical structure of the nerve,) a chemical called acetylcholine bridges the gap and stimulates the next nerve ending. A chemical called acetylcholine esterase (AchE) returns the synapse to its unexcited state. A pesticide such as an organophosphate (OP) binds with the AchE and prevents the synapse from returning to an unexcited state. The result is the insect’s nervous system goes crazy, making it nonfunctional. Insects can develop resistance by producing more AchE, providing some to bind with the OP and some to carry on the normal function of the synapse. There may be a fitness cost to this increased production of AchE such as a shorter lifespan or fewer eggs laid. Alternatively, insects can change the shape of the binding area for AchE so that the OP molecules can’t bind with it and disrupt it (decreased target site sensitivity.)

September / October 2020

How is Resistance Measured?

Researchers do what we call a bioassay. We expose the insects to a range of concentrations of the insecticide and see what level of that chemical kills 10%, 50% and 90% of them. For California red scale, we found that if we dipped fruit infested with 1st instar scales and let it sit for 14 days, the live scales molt into 2nd instars and the dead ones do not molt. We found that > 95% of susceptible scales were killed by 10 ppm Lorsban (chlorpyrifos) (Figure 1, see page 5). We reared an OP-resistant population and tested it, and nearly all scales survived 10 ppm (70-fold resistance.) We then used 10 ppm to test many field populations and if more than 10% of those scales survived that concentration then we declared that population had resistance. Very often, resistance isn’t in every insect or isn’t dominant, so only some of the individuals survive treatments. What that means in the field, is that the treatment only kills part of the population and the population ‘comes back’ or increases rapidly. What you perceive is a loss of residuality of the chemical. A chemical that lasted many weeks or several generations now only lasts a few weeks. That shortening of residual control is one of the first field indicators that a pest has resistance.

Does Resistance Go Away?

It depends on the insect life cycle, the type of inheritance and how frequently growers use the insecticide. In the case of California red scale in citrus,

Figure 1. Resistant scales were 70 times more likely to survive a concentration of 10 ppm than susceptible scales.

OP resistance is probably genetically dominant. In addition, California red scale don’t move around much so there isn’t much of a chance for the resistant individuals to interbreed with susceptible individuals and help the resistance decline. In addition, for many years, growers continued to use OPs for citricola scale, so even though the California

red scale was no longer targeted, it was getting exposed and selected regularly.

We have had a resistant colony in the lab for decades and it hasn’t been treated with insecticides and the scales still have resistance. In contrast, we have been testing California red scale for Esteem (pyriproxyfen) resistance for many years and we only see slight increases in sur-

vival (20 to 30% of individuals surviving 1 ppm.) This suggests that the resistance is not dominant. But in spite of the non-dominance, 20 years of Esteem use is taking its toll and growers are not seeing the levels of residual control they once saw.

Continued on Page 6

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Continued from Page 5

How Fast Does Resistance Develop?

in the 1980s, resistance to pyrethroids tances in citrus pests yet. One advantage in the 1990s, and some populations have of organics is that they are so short-lived now developed resistance to Delegate. In it’s not a strong selection pressure. So, contrast, citricola scale didn’t develop you will see resistance only where they resistance to OPs until the 2010s beare sprayed very frequently. cause it only has one generation per year.

It depends on several factors: Is the resistance dominant; Is the life cycle of the insect long or short; is the insecticide persistent and how often is it sprayed?

Growers do not have control over the first two factors, but they can control the third and fourth factor. Citrus thrips develop resistance fast because they have many short generations per year.

They developed resistance to DDT in the 1940s, resistance to OPs and carbamates

What Is Cross Resistance?

Can Resistance Develop to Organic Products?

The short answer is yes, given enough time and applications. But we don’t know of any organic insecticide resis-

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Cross resistance occurs when the insect uses the same method of resisting two different pesticides. This is common for insecticides in the same mode of action group. For example, all OPs and carbamates (dimethoate, Lorsban, Carzol, Sevin) attack AchE. So, if the insect develops resistance to one of them, it develops resistance to all in that group. It is very important to manage resistance by rotating between different chemical modes of action so that the insect population has to use different methods to battle the chemicals and becomes overwhelmed. The insecticide label, the IRAC Insecticide Mode of Action Classification system (www.irac-online.org) and the UC IPM pest management guidelines for citrus (www.ipm.ucanr.edu/agriculture/citrus) provide the mode of action numbers for each insecticide.

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September / October 2020

The best way to slow resistance is to use insecticides as infrequently as possible and to rotate between different chemical classes. Keep your trees healthy, pruned and watered. Remove shiners to avoid creating insectaries in the trees. Utilize pheromone disruption for California red scale. Release natural enemies and/ or use soft pesticides that allow natural enemies to survive and assist with control. Wait to treat until pests have reached treatment thresholds. Apply the insecticide carefully so that the right type of coverage is achieved, and time it so that it will have the greatest impact on the population. Finally, rotate between insecticides that have different modes of action. These integrated pest management methods will help keep insecticides useful for many years.

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Passing the Baton at UC Lindcove Research and Extension Center

Grafton-Cardwell’s tenure leaves indelible mark on the California citrus industry.

By TAYLOR CHALSTROM | Editorial Assistant Intern

A

fter 13 years as UC Lindcove Research and Extension Center’s director, Beth Grafton-Cardwell has retired, capping a career that brought significant research milestones to the California citrus industry. Lindcove REC in July named Ashraf El-kereamy as the new director.

Grafton-Cardwell’s contributions to Lindcove REC included improvement and expansion of facilities as well as expansion of the research and extension program.

“During my time there, UC ANR built a laboratory and we partnered with the Citrus Research Board to upgrade the packline fruit grading system, build a Citrus Clonal Protection Program greenhouse and screenhouse, and build a 4-acre screenhouse to protect citrus from huanglongbing,” Grafton-Cardwell said. “The screenhouse (citrus under protective structure, or CUPS) will be used by researchers to study the impact the screen shading has on the growth and development of citrus and whether citrus can be economically produced inside these structures.”

Grafton-Cardwell’s past achievements leave big shoes to fill for El-kereamy. Growers and researchers affiliated with Lindcove REC will likely see a smooth transition.

“I have had the pleasure of working with Ashraf Elkereamy over the last year and will make myself available to him to assist with the transition,” she said.

Grafton-Cardwell is looking forward to retirement, saying that she wants to spend more time with her family and contribute to her local community in Visalia, Calif.

However, she still plans to stay involved with Lindcove REC. “I will assist with the conference center enhancement funding campaign at Lindcove called ‘Sweetening the Future of Citrus’,” she said.

New Director

El-kereamy has a great deal of experience entering the director position. He studied horticulture and pomology at Ain Shams University in Cairo, Egypt, and earned a doctorate in agriculture from Toulouse University in France. He has held multiple leadership positions with research and extension programs as well as been a cooperative extension specialist with UC Cooperative Extension since 2014.

Beth Grafton-Cardwell served as director at Lindcove REC from 2006-2020 (photo courtesy B. Grafton-Cardwell.)

Ashraf El-kereamy is looking forward to continuing Lindcove REC’s innovation within the citrus industry (photo courtesy Ashraf El-kereamy.)

“During my working within the cooperative extension, I got more fascinated with the UC ANR mission and the amazing relationship between the UC academics and the California agriculture industry,” El-kereamy said. “I was ambitious to take a further step towards getting involved more in the UC ANR mission by leading Lindcove REC as one of the significant research and extension centers. My research programs since my graduation and all throughout my academic timeline have always been fashioned to help the agriculture industry.”

As director, El-kereamy has impressive visions and goals for Lindcove REC. “My goal is to lead Lindcove REC to be one of the national and international centers of excellence in citrus research and extension,” he said. “I am looking forward to leading Lindcove REC and providing our industry with up-to-date, science-based technologies to cope with the challenges facing California agriculture nowadays.”

Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

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Argentine Ant Biology and Management in Citrus

By MARK S. HODDLE | Extension Specialist in Biological Control, UC Riverside

A

rgentine ant, Linepithema humile (Hymenoptera: Formicidae), is, as its common name suggests, native to South America. The evolutionary area of origin for Argentine ant is thought to be the Paraná River basin. This is a massive area that encompasses parts of Argentina, Bolivia, Brazil, Paraguay and Uruguay, and through which the second largest river in South America, the Paraná River, and its tributaries run.

Argentine ants feeding on biodegradable hydrogel beads infused with 25% sucrose solution and 0.0001% insecticide (photo by Mike Lewis, UC Riverside.)

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Movement of soil (possibly as potted plants or ballast) by humans likely translocated Argentine ant from this native range into areas where it did not occur naturally. Argentine ant is an extremely successful invasive pest and is recorded from at least 15 different countries on six different continents and several oceanic islands. The first records of Argentine ant in southern California are from around

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September / October 2020

1905. Argentine ant populations in California, Japan and around the Mediterranean (and possibly populations in the Azores, Madeira, Canary and Cape Verde Islands) represent a “super-colony” as workers display very little aggression

Continued on Page 10

Argentine ant worker (photos courtesy Mike Lewis, UC Riverside.)

Continued from Page 8 to each other but react aggressively towards Argentine ants that originate from outside of this geographic area.

It is thought that low levels of genetic variation between these populations are responsible for this behavior, which could be the result of accidental frequent exchanges of ants between these areas by humans. The range of this “super-colony” spans thousands of miles; in contrast, in the native range, colony boundaries are typically less than 100 yards around the nest.

Argentine ant proliferates in areas with Mediterranean climates which are characterized by warm dry summers and cool wet winters. An affinity for areas with damp soils have enabled Argentine ant to thrive in agricultural and urban areas which normally would be very dry, but are now favorable because of irrigation. Natural riparian areas are also vulnerable to incursion. Invasive Argentine ant populations tend to have multiple queens (they are polygynous) which inhabit several interconnected nests (nests are polydomous.) A nest is

composed of reproductive queens and male ants, workers (all of which are females), and brood (ant larvae and pupae.) Mating occurs within nests, and ants naturally spread by budding off from existing colonies and not through flight. Each spring, around 90% of queens are executed by nest mates, and those that are killed tend to have the lowest levels of reproductive output.

Food for Protection Deal with Sap-Sucking Pests

Argentine ants are specialized liquid sugar feeders. A mounting body of evidence suggests that plant- and insect-derived carbohydrates, especially sugars like sucrose and glucose, are the primary nutrients that support Argentine ant populations. In cropping systems, these sugars are widely available in the form of honeydew, a waste product exuded by phloem or sap-feeding pests like mealybugs, scales, aphids, whiteflies and psyllids.

As a result of this feeding ecology, the behavior of Argentine ant results in the

An Argentine ant worker attacking Tamarixia radiata, a parasitoid that attacks Asian citrus psyllid nymphs (photo courtesy Mike Lewis, UC Riverside.)

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protection of sap sucking pests from natural enemies as ants patrol their herds of micro livestock and kill or chase away predators and parasitoids that feed on sap sucking pests. This food-for-protection mutualism facilitates pest population growth as an important source of mortality; death from natural enemies is greatly reduced.

Tending ants increase pest survivorship in other ways as well. Ants move pests to new feeding sites. They stimulate honeydew production via antennation which increases rates of phloem consumption and subsequent development or reproductive output, and removal of sugary waste reduces drowning risks and death from fungal contamination.

The protection Argentine ants provide to sap sucking pests in citrus is well documented and typically results in economic damage if pest mitigation is not undertaken. Recent studies conducted in Southern California have reported a strong association between Argentine ant and Asian citrus psyllid, the vector of the bacterium that causes a lethal citrus disease, huanglongbing.

Liquid bait stations hold sugar water laced with ultra-low concentrations of insecticide. Ants drink the poisoned sugar water and return it to the nest where it is shared with nestmates. This communal food sharing results in the poisoning of entire nests (photo courtesy Mike Lewis, UC Riverside.)

Attendance of Asian citrus psyllid colonies by ants results in lower rates of parasitism and reduced predation which results in larger colony sizes.

Monitoring Argentine Ants

Preliminary work from our lab suggests that once the number of Argentine ants ascending and descending the trunk of a citrus tree exceeds 15 to 20 ants per minute, biological control services decline. When ant numbers are lower than this critical density, field trials suggest that natural enemies provide extremely effective control of sap sucking pests. Two important things to consider here are: 1) How do you monitor ant numbers in citrus orchards, and 2) How do you control pest ants?

Continued on Page 12

Argentine ants tending a colony of Asian citrus psyllid nymphs. Ants harvest the solid white honey dew secreted by nymphs and, in return for this food, protect nymphs from natural enemies (photo by M. Hoddle.)

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Control Options

Continued from Page 11 One way to estimate ant numbers foraging in citrus trees is to count ants running up and down tree trunks for one minute and then averaging counts to get an estimate of the mean number of ants moving in and out of the canopy. Counting ants while kneeling or sitting on the ground under the tree canopy is extremely tedious, time consuming and inaccurate as counting fatigue quickly sets in. An alternative approach our lab is developing, in cooperation with computer engineers at UC Riverside and financial support from the California Department of Pesticide Regulation, is to use infra-red sensors mounted to irrigation pipes to count ants. Argentine ants use pipes as super highways to move between trees and nests. Sensors in waterproof housing and clamped to pipes count ants and transmit count data to a virtual cloud where it’s summarized and accessible via an app on a smart device.

These types of data summaries provide ant density estimates that are specific to orchard blocks which could potentially facilitate treatments targeted to specific areas within an orchard.

With respect to citrus, there is one insecticide registered for ant control, chlorpyrifos. However, use of this broad-spectrum contact insecticide is being phased out and use in California will be eliminated in 2021. Liquid baiting programs that capitalize on the Argentine ant’s appetite for sugar water can provide very effective ant control. Liquid baits are made from 25% sucrose solution laced with ultra-low concentrations of a water-soluble insecticide (0.0001%). Ants imbibe the toxic solution from a liquid bait dispenser and return it to the nest to feed queens and other workers.

Communal food sharing poisons nest mates and ant colonies quickly die. Our lab recently completed a multi-season liquid baiting program in six commercial citrus orchards in Southern California. Ant activity fell by 92% within two months of treatment and was, on average, 95% lower in treated plots when compared to untreated plots across the 18-month study period. Ant control resulted in the near elimination of sap sucking pest populations on trees in treated plots. Comparison of pre- and post-treatment estimates of pest (hard and soft scales, mealybugs and Asian citrus psyllid) infestations of twigs, flush growth and fruit decreased by 97%, 84%, and 99%, respectively, after treatments were applied.

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September / October 2020

A prototype infrared sensor attached to an irrigation pipe in a commercial citrus orchard (photo by M. Hoddle.)

To maintain this level of control over an 18-month evaluation period, liquid baits were replenished on an approximately monthly basis. The dramatic reduction in pest numbers was attributed almost entirely to natural enemies that were able to access pest colonies once Argentine ant had been eliminated.

As effective as these treatments were, purchasing, cleaning, replenishing and redeploying liquid bait stations full of toxic sugar water is not economically feasible.

An alternative approach we are investigating is the miniaturization of liquid bait stations for delivery of toxic sugar water. In collaboration with chemical engineers at UC Riverside and financial support from the California Department of Pesticide Regulation, we evaluated the efficacy of biodegradable alginate hydrogel beads infused with sugar water and insecticide as a delivery tool to control Argentine ant in commercial citrus orchards. Beads are broadcastable and are dispersed under trees onto soil.

Field trials indicated that three applications of beads three weeks apart over summer significantly reduced ant activity in hydrogel-treated trees when compared to non-treated trees.

Ant suppression was achieved approximately 48 hours after hydrogel applications, and ant activity was reduced by around 91% in comparison to untreated trees. Ant densities were 70% lower from pre-treatment levels three weeks after the last applications were made, indicating that there was prolonged suppression after treatments ceased.

Hydrogel beads as an insecticide delivery tool provided excellent control of Argentine ant and delivered an estimated 99.99% less insecticide into orchards when compared to commercial barrier spray treatments.

efits of ant control, especially increases in free pest control provided by natural enemies. The major impetus for this work is to find alternatives to chlorpyrifos for control of pest ants in citrus.

However, the results of work discussed here may be applicable to other cropping systems, especially perennial tree

(avocados and cherimoyas) and vine crops (grapes), which have sap sucking pest infestations that are exacerbated by sugar feeding ants.

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At this time, work continues on developing and evaluating new tools for monitoring and controlling Argentine ant in citrus and documenting the ben-

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RESEARCH AND EXTENSION FOR CALIFORNIA CANNABIS PRODUCTION

Survey of Growers Sheds Light on California Production Practices and Research Priorities

By HOUSTON WILSON | Asst. Cooperative Extension Specialist, UC Riverside

T

he recent legalization of recreational cannabis in California has introduced a unique and potentially highly valuable crop into the state agricultural landscape (UC AIC, 2017).

After nearly three years, state regulatory agencies and academics alike are still scrambling to address the ecological, social, economic and agricultural effects of this “new” commodity.

As with other agricultural crops, cannabis production could benefit from the development of a collaborative research and extension program that brings together growers, experts from the University of California and other industry stakeholders. Unfortunately, the continued federal prohibition of cannabis production has largely restricted the development of such efforts within the UC system. As a land-grant university that receives federal support, any UC effort to improve the yield, quality or profitability of cannabis production is strictly prohibited, thus placing the University in a strange limbo when it comes to engaging with the cannabis industry, and with cannabis production systems in particular. This is in contrast to industrial hemp, which is federally legal and has generated lots of interest recently amongst growers and UC scientists alike.

It almost goes without saying that cannabis production has taken place for decades in California, and in the absence of any UC or other state support growers have obviously been quite successful on their own at developing countlessly innovative methods to improve production and crop quality. Furthermore, the cannabis industry has even found novel ways to self-organize, share information and provide training opportunities through such networks as the California Growers Association, International Cannabis Farmers Association and Oaksterdam University, the latter a rigorous (but non-accredited) university-style 14

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training program that offers certificates in cannabis production, manufacturing, marketing and sales.

While legalization of cannabis has provided growers the opportunity to more freely produce and potentially expand the market for their crop, cannabis is also now subject to a wide range of agricultural and environmental regulatory measures. The potential costs and benefits of such tradeoffs were part of an intense debate amongst growers and other industry stakeholders leading up to the Proposition 64 vote in November 2016.

While unable to directly engage with cannabis production, UC researchers have been able to study the geography and environmental impacts of these cropping systems, and in doing so have documented some negative effects of cannabis production on waterways, natural habitats and wildlife (Butsic and Brenner, 2016; Bauer et al., 2015; Carah et al., 2015; Levy, 2014; Gabriel et al., 2012).

It is important to note here that these environmental impacts are not necessarily unique to cannabis agriculture or representative of all cannabis growers, but nonetheless some of these production systems in their current form may significantly threaten environmental quality and sensitive species in the watersheds where cannabis is grown (Butsic et al., 2018).

As mentioned, with legalization comes the imperative to bring cannabis production into compliance with a range of state agri-environmental regulations.

While many growers are making diligent attempts to do so, these efforts could be further supported through a UC research and extension program to develop science-based best management practices to mitigate or avoid impacts as well as provide additional training opportunities to help growers adopt these practices.

September / October 2020

This is especially important as more states continue to legalize recreational use and thus expand markets for California-grown cannabis, which currently represents about two-thirds of total domestic production (NDIC, 2009).

While some broad information publicly exists on cannabis cultivation (e.g.

Rosenthal, 2010), few scientific studies have attempted to document more specific aspects of production. Like any cropping system, understanding the nature of cannabis production is the first step toward identifying areas for improvement in order to reduce environmental impacts of these farming systems.

Online Survey of Cannabis Production

Recently, a team of UC researchers developed an online survey (http://ucanr.edu/ sites/cannabis/) to characterize cannabis cultivation techniques, pest and disease management, water use, labor practices and regulatory compliance (Wilson et al., 2019). The idea behind this survey was to generate data that would serve as a baseline for the development of a research and extension program to support best management practices to reduce environmental impacts of production.

A link to the survey was distributed via email through self-organized networks of California cannabis growers that were willing to participate and endorse this effort. In total, the survey was distributed to more than 17,000 unique email addresses, although certainly not all recipients were cannabis growers, and there was probably some overlap between the different mailing lists. All survey participants remained anonymous, and response data did not include any specific participant identifiers.

Ultimately, just over 100 surveys were partially or fully completed, representing a range of growers from across the

state including the North Coast, Bay Area, Central Coast, Sierra Foothills and Southern California. While findings from this survey were verified by growers as generally accurate, these data should of course be taken as a starting point to guide a more detailed exploration of specific practices in the future. What follows is a summary of the key findings, and full results of the survey can be found online (http://calag.ucanr.edu/ archive/?article=ca.2019a0015).

Survey Findings

A majority of the farms were small (<10,000 square feet) and had been growing cannabis on the same piece of land for multiple years. Most were outdoor farms followed by combined outdoor and greenhouse production. Average cannabis yield was about 1 pound per plant, but varied by growing condition, with outdoor and greenhouse crops producing the highest and lowest yields per plant, respectively. While greenhouse production represented a smaller fraction of growers and lower total yield per plant, these systems actually tended to have a higher total yield per square foot due to the increased density of plants and more rapid production cycles (i.e. multiple crops per year.) Most growers operated only a single farm and had been growing cannabis for about 15 years.

Groundwater was the primary source of irrigation for respondents in this survey.

Most reported using variable amounts of water across the growing season (less in spring/fall, more in the summer.) During the summer an average of about 5 gallons per plant per day was applied. When adjusted for planting density, this equates to about 0.17-0.22 gallons per square foot per day.

Growers reported the use of many different soil amendments and foliar nutrient sprays. The most common were organic fertilizer, animal manures and meals, compost tea and worm castings.

Crop damage from insects, pathogens and/or vertebrates was highly variable.

The most common arthropod pests were mites, thrips, aphids and, to a lesser extent, unknown larvae. Vertebrate pests included gophers, mice, rats, deer and even wild boars. Powdery mildew was by

far the most commonly reported disease followed by molds and rots. Pest and disease control mostly relied on the application of a solution or chemical to the crop, although about one-third of growers also reported use of beneficial insect releases and various cultural practices like sanitation and insect trapping. Crop sprays mostly consisted of biologicals or other products approved for organic production, such as microbial pesticides, oils and azadirachtin. Disease control was primarily through the use of sulfur.

Future Directions for Cannabis Research and Extension

Albeit small, this is the first known survey to formally characterize California cannabis production practices, and the broad dataset it provides will serve as a starting place for more in-depth work with growers around key issues like water use, pest management and crop nutrition.

There is clearly a need for more information in order to develop best management practices to achieve natural resource stewardship goals and compliance with state agri-environmental regulations.

The historically (and understandably) clandestine nature of California cannabis production tended to push these cropping systems into isolated remote areas, many of which fall within sensitive natural habitats. While studies subsequently documented negative impacts of cannabis production on these environments, it is important to emphasize that these outcomes are likely not inherent to cannabis production itself, but rather simply due to siting decisions. Furthermore, given the lack of a well-developed research and extension program to identify best management practices, it is not surprising that some cannabis production systems generate off-farm impacts. Remarkably, in the absence of clear guidance, it appears that many cannabis growers have responded by adopting a number of environmentally proactive approaches to production on their own, and even creating their own training and extension networks to share information on best management practices.

Grower organizations that participated in this survey were comprised of a relatively large base membership that represents a diverse and engaged cannabis production September / October 2020

community. Additionally, growers who completed the survey were clearly knowledgeable about cannabis cultivation, and many expressed an interest in further improving the environmental quality of production practices. As such, a research and extension program for California cannabis production could help identify and refine best management practices in order to minimize negative impacts of production on farm workers, the environment and surrounding communities.

Today, multiple efforts to engage with various facets of the cannabis industry have been initiated within the UC, but for the foreseeable future many of these programs will need to carefully navigate this space in a way that keeps their activities compliant with federal cannabis regulations.

References

Bauer, S., J. Olson, A. Cockrill, M. v Hattem, L. Miller, M. Tauzer, and G. Leppig. 2015. Impacts of surface water diversions for marijuana cultivation on aquatic habitat in four northwestern California watersheds. PLoS ONE 10(3): e0120016.

Butsic, V., and J. C. Brenner. 2016. Cannabis (Cannabis sativa or C. indica) agriculture and the environment: A systematic, spatially-explicit survey and potential impacts.

Environmental Research Letters 11: 044023.

Butsic, V., J. K. Carah, M. Baumann, C. Stephens, and J. C. Brenner. 2018. The emergence of cannabis agriculture frontiers as environmental threats. Environmental Research Letters 13: 124017.

Carah, J. K., J. K. Howard, S. E. Thompson, A. G. S. Giannotti, S. D. Bauer, S. M. Carlson, D. N. Dralle, M. W. Gabriel, L. L. Huletter, B. J. Johnson, C. A. Knight, S. J. Kupferberg, S. L. Martin, R. L. Naylor, and M. E. Power. 2015. High time for conservation: Adding the environment to the debate on marijuana liberalization. Bioscience 65(8): 822–829.

Gabriel, M. W., L. W. Woods, R. Poppenga, R. A. Sweitzer, C. Thompson, S. M. Matthews, J. M. Higley, S. M. Keller, K. Purcell, R. H. Barrett, G. M. Wengert, B. N. Sacks, and D. L. Clifford. 2013. Anticoagulant rodenticides on our public and community lands: spatial distribution of exposure and poisoning of a rare forest carnivore. PLoS ONE 7(7): e40163.

Levy, S. 2014. Pot poisons public lands. Bioscience 64: 265–271.

[NDIC] National Drug Intelligence Center. 2009. Domestic Cannabis Cultivation Assessment. U.S. Department of Justice NDIC. www.justice.gov/archive/ndic/pubs37/37035/ index.htm Rosenthal E. 2012. Marijuana Pest and Disease Control: How to Protect Your Plants and Win Back Your Garden.

Quick American Publishing, Oakland, CA. [UC AIC] UC Agricultural Issues Center. 2017. Economic Costs and Benefits of Proposed Regulations for the Implementation of the Medical Cannabis Regulation and Safety Act (MCRSA). http://www.dof.ca.gov/Forecasting/ Economics/Major_Regulations/Major_Regulations_Table/ documents/SRIAandAppendix.2.28.17.pdf Wilson, H., H. Bodwitch, J. Carah, K. Daane, C. Getz, T. E. Grantham, and V. Butsic. 2019. First known survey of cannabis production practices in California. California Agriculture. 73(3): 119-127.

For more information and updates on this work, visit the UC Berkeley Cannabis Research Center (https://crc.berkeley. edu/) and the UC Davis Cannabis and Hemp Research Center (https://cannabis.ucdavis.edu/).

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15

The Art of Fertilization: Making Decisions on Nutrition

By FRED STRAUSS | WRCCA Board of Directors

C

ertified Crop Advisors make decisions about fertilizing crops every day. It appears these decisions are made in minutes, but little do people know all that goes into these processes.

Working with many crops and having the choice to fertilize or not can vary quite a bit. This article looks to give an overview into what goes on in the CCA’s mind while deciding to fertilize or not, how much, when, where, which application system to use and many other factors.

You can find information on fertilizer need by crops in places such as the Western Fertilizer Handbook, university informatoin, Farm Advisors, commodity groups, fellow CCAs, growers and your own experience and expertise.

People think the answers come from a book on that crop, or what a CCA learned in school. I believe the CCA takes all their schooling, training and experience and puts it on a canvas just like an artist does. Let’s look at these artists at work.

Considerations Based on Nutrients

Are the fertilizer considerations the same for all crops? Certainly not, but very close. California and Arizona are so diverse in crops with over 300 different crops, and subsequently diverse in inputs for those crops. Twenty-five million acres are farmed in California, generating $53 billion in sales. The next nearest state generates $35 billion and grows 20 million acres just in corn. The number of different crops makes California’s CCAs very valuable and the demand for their expertise goes up every day.

For the sake of this article, let’s simpli16

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fy things by focusing on one crop and walking through the steps a CCA might go through in making fertility decisions.

Let’s pick a block of almonds and say it is sometime in January heading into a new season. We have farming in California 365 days a year and seasons are related to the crop rather than the time of year. Almonds do have a growing season which generally gets going in February with bloom and harvest in August through October. So, how much fertilizer does an Almond crop require, and what about the variety and potential yield?

Establishing a yield estimate provides an excellent starting point for assessing fertilizer need. Crop yield and crop-specific fertilizer demand is a good starting point, but the next big factor in determining how much fertilizer you need is the soil.

Good soil samples help lay out what you have. Soil type and the quality play a big role in the movement of the fertilizer and availability.

Certain attributes in the soil can tie up fertilizers like sodium levels, pH levels, Boron, salts and more. Heavy soils, loamy soils, sandy soils, high organic matter or very low organic matter all play a role. It should be remembered that the soil fills some of the nutrient needs so it can reduce the fertilizer you need to apply as well as what type of fertilizer to apply.

Water also provides some nutrients, some good and some bad. You need to know the source of the water. Is your water from a well, district irrigation water or even recycled water? Having a water sample will identify the quality as well as any issues. Does the water need September / October 2020

to be mediated because of pH levels or salts? Do you need soil amendments in the winter time to offset some issues that your water creates?

Check Your Program

It’s nice to keep track of how your fertilizer program is doing during the season so as to not operate in the blind. Doing leaf samples in season will help determine if your fertilizer program is working, so, when you go to your grower, you are speaking from some level of confidence. When looking at the leaf samples we are not only looking at N, P and K, but our minor, micro and macro nutrients as well. Foliar applied nutrients in season can fine-tune some of the issues raised by samples. Foliar nutrients can be tank mixed with other products being applied, but timing can be important.

Biologicals are becoming a bigger factor in all areas of fertilization, but perhaps none more than in foliar nutrients.

There are many ways to apply fertilizer.

If I can apply through the irrigation system then I save an application step.

Most almonds use micro irrigation or drip. It’s an easy way to apply fertilizers and spoon feed the crop in season. By spreading out applications through the season, I avoid oversaturating the soil and leaching beyond the root zone. We are also applying the fertilizer near the trees and not outside the dripline.

Give the trees what they need, when they need it and from the right source to avoid any problems. To make this decision, a good rule to go by is the 4Rs, a program developed by the International CCA Board that helps determine the right product, right amount, right time and right place.

WE HAVE LEARNED SO MUCH OVER THE LAST FEW YEARS ABOUT THE BEST TIME TO FERTILIZE FOR MAXIMUM UPTAKE AND TO AVOID NEEDLESS APPLICATIONS AND LEACHING.

The right time to fertilize is another important factor. One of the most important times to fertilize is usually pre-bloom, assuming the crop you watch has a bloom stage. In almonds, a fertilizer application right after harvest is very important. Enough should be put on so the trees come out strong the next season, a common industry practice. We have learned so much over the last few years about the best time to fertilize for maximum uptake and avoid needless applications and leaching. Some people

“

are trying to restrict when we fertilize not realizing it is OK to pre-fertilize or post-fertilize a crop. How you do it is as important as when.

These tracking and application methods lend themselves to sustainability.

Having fewer applications by tractors, confining our nutrients where they are needed, applying our water where it is needed, and simply reducing our carbon footprint are the best courses of action. By using all the sources of in-

September / October 2020

formation available, leaning heavily on schooling, training and experience, we can grow great crops sustainably and profitably. As a Certified Crop Advisor, you have a responsibility to do what is right and what is best for your grower and the environment.

Remember that you are the artist.

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17

Soil Health Field Trials at West Hills College Coalinga Healthy soils are key to productivity and soil

and water conservation

By TIM ELLSWORTH, PH.D. | Ag Science Instructor, West Hills College Coalinga

M

ention “soil health” to a grower and they may recognize its value, but may not understand exactly what it is or how to get there.

Mention soil health to a soil scientist and you’ll likely get an hour lecture on how it needs to be done. Soil health, or regenerative agriculture, is a growing priority, and its central tenets is a soil that is robust, resilient and capable of performing desired ecosystem functions such as nutrient cycling and sustaining plant health. The components of a healthy soil include biota, organic matter, porosity and aeration, and a balanced chemistry.

Soil 101 says that soil is composed of inorganic minerals in the form of sand, silt and clay. It also includes microorganisms and organic materials in the form of humus and decomposing matter. The spatial arrangement of these components creates the soil structure and the associated soil pore space which often comprises half of the total soil volume and through which water and air move into and out of the soil. The fraction of pore space is a critical factor regulating soil health, as is the topology of the pore space. The latter refers to the spatial arrangement and interconnections within the soil pore network that govern the rate of water infiltration and air exchanges with the atmosphere. The percentage of each of these components within a soil is what determines the type, texture, productivity and many of the characteristics of soil health. A healthy soil has a pH between 6 to 7.5, adequate cation exchange capacity with a proper balance of basic cations (e.g., calcium, potassium, magnesium), relatively low salinity, an appropriate balance of plant nutrients in both organic and inorganic forms, a pore distribution that ensures adequate 18

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infiltration rates and water retention for crop production, and organic matter and associated microbial communities that buffer and sustain plant nutrient requirements.

West Hills College Coalinga (WHCC) Farm of the Future (FoF) has made healthy soils a focus because of its importance to productivity and soil and water conservation. Fundamental concepts are taught in several courses: Introduction to Soil Science, Soil Amendments and Plant Science. To support this instruction, the FoF is looking for partners to demonstrate to students, products or practices that improve soil health using demonstration research projects.

These projects teach students about research methods and new technology. WHCC is in an excellent position, as a college known for hands-on learning, to serve as an unbiased third party for evaluating new products and the practical side of research.

Broccoli soil health plots at West Hills College Coalinga (photo courtesy T. Ellsworth.)

Soil Health Teachings and Research

Recently, WHCC had the opportunity to test a new soil amendment product that is promoted to enhance nutrient and water-use efficiencies.

Field trials suggest the product duplicates the effect that organic matter has on soil structure and nutrient and water use

Continued on Page 20 September / October 2020

West Hills College Coalinga (WHCC) Farm of the Future (FoF) has made healthy soils a focus because of its importance to productivity and soil and water conservation.

Calcium Improve water penetration Apply the convenient liquid formulation of CaTs® during the dormant season for easy calcium application ahead of winter rains.

The 100% soluble calcium and thiosulfate immediately begin displacing sodium and flocculating soil colliods. Prepare your fields for next season with CaTs.

Learn more about CaTs at www.cropvitality.com

Or call (800) 525-2803 - Email info@cropvitality.com ©2020 Tessenderlo Kerley, Inc. All rights reserved. CaTs® is a registered trademark of Tessenderlo Kerley, Inc.

WEIGHTS IN POUNDS (AGGREGATE 60 BROCCOLI) Block 1 N

Block 2 N

Block 3 N

Block 4 N

46.6

79

131

113.4

127.6

146.6

Block 1 S

Block 2 S

Block 3 S

Block 4 S

Block 5 S

Block 6 S

60.4

87

77.6

78

151

154.8

Block 5 N Block 6 N

Table 1. Treatment plots (green highlights) in Blocks 1, 3 and 5 had higher aggregate weights from the random 60 plants that were pulled and weighed. However, control plots in Blocks 2, 4 and 6 had higher aggregate weights. Those differences were less substantial than the differences in the treatment blocks, likely caused by a few outliers, so the net result was more aggregate weight from treatment plots.

Descriptive Statistics-Control Weight in Grams Minimum 1st Quantile 75.0

448.2

Median

Mean

3rd Quantile

Max

728.5

742.3

1009.0

1886.0

Descriptive Statistics-Zytonic Weight in Grams Minimum 1st Quantile 140.9

499.0

Median

Mean

3rd Quantile

Max

743.5

836.7

118.0

2358.0

Table 2. The descriptive statistics for all of the collected individual Zytonic and control broccoli weights.

Continued from Page 18 efficiencies. It can be described as a nano-granule polymer that is inoculated with Mycorrhizae and has a CEC value five times greater than peat moss. The product, called Zytonic, is produced by the global company Zydex. Zydex was interested in demonstrating the impact Zytonic can have on soil health to students and approached WHCC about doing a demonstration project.

Organic matter, as a carbon-based material, has the ability to bind soil particles together to create aggregates, altering the soil structure and soil pore networks. As a result, soils with higher organic matter have good tilth (e.g., crumble readily, and feel “softer”.) In contrast, soils with little to no organic matter generally have massive structure and, when tilled in a dry state break into compact, large clods.

One problem with maintaining healthy soils in the California Central Valley is maintaining organic matter and the associated microbial communities essential for nutrient cycling. In the Midwest, 20

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summer rains, cooler temperatures and higher humidity are conducive to maintaining biota and organic matter. When land in the Midwest is fallowed, cover crops grow naturally. In the Central Valley, cover crops require irrigation and higher levels of management. Fallow land typically is managed as bare ground by regular disking to control weeds; the net effect destroys microbial communities and organic matter. To reverse this trend, fallow practices that provide organic residues and sustain moisture levels are required. With water restrictions, such practices are especially challenging in annual crops while perhaps more feasible in permanent cropping systems.

Organic matter impacts other soil components and its loss results in a cyclic pattern. As organic matter disappears, maintaining balanced crop nutrition with synthetic fertilizers becomes more challenging yet is often the most viable option available. Furthermore, the loss of organic matter on the top layer of soil reduces cohesiveness which increases susceptibility to wind and water erosion and increases compaction. Erosion furSeptember / October 2020

ther aggravates organic matter losses as organic substances bound to the eroding mineral fraction are lost. Compaction in turn reduces infiltration and aeration, which reduce plant and root growth and root exudates and residue additions.

This lowers the nutrients available and requires an increase in use of inorganic fertilizer.

Zytonic Use

The product that Zydex asked us to demonstrate, Zytonic, appears to enhance pore space in soils and perform functions similar to organic matter. In addition, the product contains mycorrhizae inoculum and humic substances that may increase nutrient and water-use efficiencies. For example, arbuscular mycorrhizal fungi form a mutualistic relation with vascular plants that enhances immobile nutrient and water uptake by creating a network of hyphae that extend from the plant into the soil (hyphae are slender filaments somewhat similar to root hairs.)

A one-acre plot was laid out by WHCC students into 6 rectangular blocks, each

than the largest plant from control.

The graph in Figure 2 indicates that all descriptive measures of individual plants from the treatment plots were larger than those from the control plots.

The smallest plant from treatment was almost twice the weight of the smallest plant from control; the largest plant from treatment was almost 500 grams heavier

Density

Running a Welch t-test, Nick found a p-value of 0.028 which is below the 0.05 threshold level, so he rejected the null hypothesis. This means there is a statistically significant difference between the groups, with the Zytonic-treated plants being

Zytonic Control

0

500

1000

1500

2000

2500

Weight

Figure 2

Continued on Page 22

You’re already preparing for next year’s crop.

We’ve got you covered.

Literally.

Row Crop Production students assisted in the plot, though the COVID-19 pandemic developed during the study.

As a consequence of the home sheltering directive, staff completed the harvest and data collection. To minimize risk, only one sampling date was used which resulted in much of the product being harvested prematurely.

For this initial research demonstration, the weight of the product was the key indicator. 60 random sample plants were sampled with roots from each block plot and weighed for an aggregate. 30 random plants were then selected for individual weights for each plot. Nick Trujillo, FoF Research Analyst, helped to complete harvest, data collection and analysis of the data. Table 1 provides the descriptive statistics for the aggregate weights. Table 2 provides the descriptive statistics for all of the collected individual Zytonic and control broccoli weights:

Distribution of Weights 0e+00 2e-04 4e-04 6e-04 8e-04

of which were divided in half. For each of the six blocks, halves were randomly assigned to a treatment or control plot.

Students from Introduction to Plant Science hand-planted broccoli plants in the field (approximately 21,000 plants.)

Students assigned to the project, assisted by Dr. Tim Ellsworth, applied pre-emergence herbicide and manually weeded the plots. Soil Amendments and Fertilizers students mixed and applied the Zytonic to the treatment plots in a water solution. The Soil Amendment and Fertilizer students also used the broccoli experiment to do a fertilizer response demonstration by applying 100% of the recommended fertilizer rate to blocks 5 & 6, 75% to blocks 3 & 4, and 50% to blocks 1 & 2 (note these treatments were not randomly assigned so this was merely a demonstration aspect of the project.)

Plants were watered using the FoF sprinkler system uniformly over all blocks and plots.

51%

increased weed control* for conventional herbicides

79%

increased weed control* for organic herbicides

Ampersand® adjuvant’s unique delivery system uses a high contact angle and high surface tension, the opposite way of how other adjuvants work, to implement our 4-prong approach to get your active to the target and keep it there longer for an epic post-harvest burndown.

Typical Surfactant

Ampersand®

Drift Control

Deposition Aid

Evaporation Protection

Wash Off Resistance

Less fines and large droplets result in three times more spray to the leaf.

Ingredients that provide adhesion keep droplets from rolling off the leaf.

Humectants keep actives in a liquid state twice as long as typical surfactants.

Actives are protected four times longer from rain and overhead irrigation.

Ampersand

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www.attuneag.com *with the addition of Ampersand; compared to active alone

September / October 2020

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21

Broccoli root hairs from the treatment area (left) were more pronounced than broccoli root hairs from the control plots (right).

Continued from Page 21 significantly larger.

Nick further examined the locations of the blocks to see if any differences were present there as well. Using the same alpha level from before, he tested to see if there was a difference between the North and South blocks (comparing all the North blocks to the South blocks.)

This resulted in a Welch t-test p-value of 0.23 which means there is no statistically significant difference between the North and South block broccoli weights.

This means there isn’t an effect from the North or South position being picked up in the Zytonic broccoli weights. Because the fertilizer rate treatments were not randomly assigned, it is not valid to do a similar analysis for the observed differences between East and West blocks. However, there is a clear trend of increasing broccoli weights with increasing fertilizer rate.

Because the Zytonic was applied at randomly assigned blocks, we can utilize

22

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a basic linear regression model to get at the casual effect of the Zytonic applications. That is, what is the estimated effect of the Zytonic application on the broccoli weights? When we test a basic linear regression model, we find that the Zytonic application had a positive effect of 94.44 grams and a p-value of 0.0288.

This means the effect of the Zytonic application is statistically significant and is causally increasing the weights of the broccoli by 94.4 grams when it is present in the soil. This means Zytonic has a positive effect on weights.

An unexpected result is the growth of root hairs. Though it was not a part of the study, as staff were pulling the broccoli from the ground, it was consistently more difficult pulling them from the treatment area. On investigation the amount of root hairs from the treatment group was much more pronounced than the broccoli from control plots. We hypothesize that this may have been due to the humic substances added or the mycorrhizae inoculum. This is something that will be investigated in more

September / October 2020

detail on the next demonstration.

The results from this one demonstration project doesn’t “prove” that the use of these polymer-based nano-granules will always increase plant growth, but the results are promising. While there are several possible mechanisms that may have led to the observed results, these have not been confirmed. We are looking forward to our next demonstration project with Zydex which will likely focus on water-use efficiency. In the upcoming project, soil moisture monitoring will be used to guide irrigation scheduling in association with water metering to develop water budgets for treated and control plots.

No final conclusions on the effectiveness of Zytonic can be made from this one small demonstration, but from the educational point of view, it was extremely valuable for WHCC FoF students.

Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

Results of 2020 Kern County Potato Variety Trial

By JASPREET SIDHU | UCCE Vegetable Crops Farm Advisor, Kern County and JED DUBOSE | UCCE Staff Research Associate, Kern County

P

Vegetable crops program team planting the trial on Feb 18, 2020 (all photos by J.K. Sidhu.)

Grading the tubers on a small potato grader. The grader helps to separate tubers into different sizes like small (0-4 oz), medium (4-6 oz), large (6-10 oz) and jumbos (>11 oz).

24

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otato is the third most important food crop worldwide and the most important vegetable crop in the US with a per capita consumption of 116 lbs. per year. In California, russet, red, white and specialty potatoes are planted or harvested almost every day of the year due to the diversity of the state’s climate.

California is the ninth largest potato-producing state in the US and is the nation’s largest producer of spring potatoes. The majority of these spring market potatoes are produced in Kern County. Sustained potato production faces several constraints such as variable environmental conditions, pest problems and market niches requiring the development of cultivars that are either widely adapted to the region or suitable for specific production areas or markets. Therefore, it is crucial to address the unique needs of the potato industry through sustained development and evaluation of new cultivars. Although California is a major producer of fresh market potatoes, the state currently lacks an organized statewide potato breeding program to accommodate the needs of California potato growers. Therefore, the California potato industry works closely with USDA and the Southwest (Colorado, Texas and California) and Western Regional programs for potato variety development and evaluation.

This project provides an opportunity for growers and breeders to see the performance (improved yields, quality and resistance) of new varieties under commercial growing conditions in Kern County because our growing conditions

September / October 2020

Different varieties side by side.

are significantly different (warmer and drier) as compared to other potato growing regions in the US. The overall aim of this project is to evaluate the adaptability of these new varieties to Southern California growing conditions for improved yields and quality, and to determine if any of the new varieties have improved resistance to common diseases, insects or environmental stress.

Trial Details and Results

There were three sub trials in this project and these trials were conducted at a grower’s field in Bakersfield, Calif. Trials were categorized as Southwest Regional Trial with 17 entries, the Kern County Potato Variety Selection Trial with seven entries, and Observational trial with 72 entries.

Southwest Regional Trial: Unlike all other potato production regions in the US, there are no USDA-ARS scientists with primary potato research responsibilities located in the Southwest. Therefore, potato research, specifically cultivar development, is the responsibility of the states within the region. A formalized agreement between the breeding and development programs in California, Colorado and Texas was established in 1997 to address the needs of the potato industry in the Southwest. This trial in Bakersfield, Calif. continues the association that the California potato industry has had with Colorado State University and Texas A&M University in the formation of the Southwest Region

Uniform, smooth-skinned tubers of variety Primabelle.

Trials. Advanced varieties are made available

by Colorado State University and Texas A&M University each year for testing in regional trials. These varieties include russets, whites, reds and specialty types. These varieties are replicated four times to minimize variations and are evaluated to have an accurate measure of their true potential for yield, quality and resistance.

Continued on Page 26

A high-yielding chipper variety from the Southwestern trial.

Electra, the high-yielding variety from Kern County replicated trail.

A high-yielding chipper variety from the Southwestern trial.

Large, yellow-fleshed, smoothskinned tubers of variety Almera

September / October 2020

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25

Overall, there were many varieties to consider trying on a small acreage basis. Some of the selections such as COTX08063-2RU (Russet), AC11467-4W (Chipper) and CO12235-3W (Chipper) from Southwestern trials performed well for yields and quality compared to standard varieties Russet Norkotah and Atlantic (Fig. 1).

COTX08063-2RU is a late-maturing russet type with oblong tuber shape while varieties AC11467-4W and CO12235-3W are mid-season in maturity, have medium vines and oval, round-shaped tubers.

ed for plant emergence and percent stand count.

All plots were harvested, graded and evaluated for tuber size, total and marketable yield.

Southwest Regional Trial

MARKETABLE YIELD (CWT/A)

250

235.5

227.5

211.5

203.3

200

150

193.2

169.8

163.5 130.1

143.4 140.2

143.4

144.4

140.3

185.7 154.9

146.3

114.9

100

At Ru la ss nt et No ic rk ot ah Yu ko n Go AC ld 11 45 3AC 7W 11 46 7AC 4W 11 49 4 AF C5 6W 72 6 -1 CO RU 12 15 21R CO U 12 23 5 CO -3 W 12 24 61R CO U 12 29 3CO 1W 12 37 81R CO U 12 4 CO 28 -2 TX W 08 06 3AT 2R TX U 07 04 2TX 3 W AO 094 03 RT -2 X0 1 W 90 37 -1 W /Y

In the Kern County replicated trial (See Figure 2), varieties Electra, Primabelle and Nectar showed good 50 potential with high yields and tuber appearance. Electra is an early maturing, fresh market variety with ovalshaped tubers. It has yellow-colored tubers with a yellow flesh and good resistance to common scab and foliage 0 Primabelle is an early maturing fresh market variety. It has attractive bright, smooth oval tubers with blight. light-yellow skin and light-yellow flesh. Nectar is an early maincrop yellow flesh variety producing uniform medium to large tubers and is excellent for both the fresh market and packing sector.

In the observational trials, there were several outstanding performers for yield and quality. Some of these were CO13232-25W, CO13033-4W/Y, Goldeye, Almera andVARIETY Sally. Goldeye is a promising early maturing yellow Fig. 1 and produces large uniform tubers. Almera emerged as one of the best varieties in the trial with high variety yield and distinctive tuber appearance.

This variety is suitable for thein fresh as well as Regional the processing Figure 1. Marketable tuber yield of potato entries themarket Southwest Trial. industry. CO13232-25W and CO13033-4W/Y were the advanced selections from Colorado State University.

Kern County Variety Trial 400 357.7

MARKETABLE YIELD (CWT/A)

350 300 250 190.2

200

205.8

199.5

207.6

157.7 150

117.7

100 50 0

CO08062-3PF/P CO11250-1W/Y

Double Fun

Nectar

Cerata

Primabelle

Electra

VARIETY

Figure 2

Figure 2. Marketable tuber yield of potato entries in the Kern County Variety Trial.

Please contact Jaspreet Sidhu, Vegetable Crops Advisor, Kern county if you would like a copy of the full report along with pictures of all these varieties. The authors would like to thank Kevin Johnston of Johnston Farms for their generosity in hosting the trial for the past several years. This work is funded by California Potato Research Advisory Board, USDA NIFA (Potato Breeding Research, award no.: 2019-34141- 30433), and Potatoes USA.

Continued from Page 25

Kern County Potato Variety Selection Trial: The Kern County trial has a ### long history and has been going on for several decades. The trial primarily consists of varieties developed by various universities and private breedCUTLINES ers from North America. Selections in the trial are replicated four times.

Varieties in the trial could be dropped after the first or second year of evaluation, or go into a final third year of evaluation based on performance.

Observational Trial: Potato varieties with little history or data will be first looked at in the observational trial. It will consist of varieties from private and public breeders to test how they perform under Kern county conditions. Varieties that have proven merit in the observational trial will likely move up to the Kern County replicated trial the following year.

The 2020 Kern County Potato Variety Trial was completed in June. The trial was planted on February 18, 2020, and harvested on June 10, 2020.

The varieties available for these trials were planted on 20-foot-long plots with 27 seed pieces (27 hills) planted on each plot. The trial received all standard agronomic practices of our grower cooperator. Data was collect26

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Varieties Used

Overall, there were many varieties to consider trying on a small acreage basis. Some of the selections such as COTX08063-2RU (Russet), AC114674W (Chipper) and CO12235-3W (Chipper) from Southwestern trials performed well for yields and quality compared to standard varieties Russet Norkotah and Atlantic (Fig. 1). COTX08063-2RU is a late-maturing russet type with oblong tuber shape while varieties AC11467-4W and CO12235-3W are mid-season in maturity, have medium vines and oval round-shaped tubers.

In the Kern County replicated trial (See Figure 2), varieties Electra, Primabelle and Nectar showed good potential with high yields and tuber appearance. Electra is an early maturing, fresh market variety with oval-shaped tubers. It has yellow-colored tubers with a yellow flesh and good resistance to common scab and foliage blight. Primabelle is an early maturing fresh market variety. It has attractive bright, smooth oval tubers with light-yellow skin and light-yellow flesh. Nectar is an early maincrop yellow flesh variety producing uniform medium to large tubers and is excellent for both the fresh market and packing sector.

In the observational trials, there were several outstanding performers for yield and quality. Some of these were CO13232-25W, CO13033-4W/Y, Goldeye, Almera and Sally. Goldeye is a promising early maturing yellow variety and produces large uniform tubers. Almera emerged as one of the best varieties in the trial with high yield and distinctive tuber appearance. This variety is suitable for the fresh market as well as the processing industry.

CO13232-25W and CO13033-4W/Y were the advanced selections from Colorado State University.

Please contact Jaspreet Sidhu, Vegetable Crops Advisor, Kern county if you would like a copy of the full report along with pictures of all these varieties.

The authors would like to thank Kevin Johnston of Johnston Farms for their generosity in hosting the trial for the past several years. This work is funded by California Potato Research Advisory Board, USDA NIFA (Potato Breeding Research, award no.: 201934141- 30433), and Potatoes USA. Comments about this article? We want to hear from you. Feel free to email us at article@ jcsmarketinginc.com

September/October 2020

V I N E YA R D R E V I E W FEATURED ARTICLES:

Control Strategies for Mealybug Pests and Vectored Viruses in Vineyards Autonomous Predictions of Vineyard Yield Chemical and Biological Control of Nematodes Affecting Grapes in the San Joaquin Valley Grape Berry Ripening and Preharvest Management

VINEYARD REVIEW

Control Strategies for Mealybug Pests and Vectored Viruses in Vineyards

By CRAIG MACMILLAN, PH.D. | Macmillan Ag Consulting and KRIS BEAL, M.S. | Vineyard Team

M

ealybugs, especially the vine mealybug, excrete a white waxy substance in clusters that is unacceptable to wineries. They also excrete a sweet honeydew that is a substrate for black sooty mold. Black sooty mold covers the fruit and the rest of the vine with a black coating. In addition, mealybugs spread Grapevine Leafroll-associated Virus 3 (GLRaV-3). Between damage to fruit and vine decline from virus, the economic impacts of the pest are substantial.

Biology of the Pest

The primary species of mealybug causing economic impacts in vineyards is the vine mealybug (Planococcus ficus).

Other species of economic concern

are the grape mealybug (Pseudococcus maritimus), obscure mealybug (Pseudococcus viburni) and long-tailed mealybug (Pseudococcus longispinus). The vine mealybug has five to seven generations per year (more than other species) and can be active year-round in warm areas, making control challenging. It also lays more eggs than other species.

Mealybugs hide under bark and on roots during the winter and hot periods during the summer. This makes most contact insecticides ineffective.

Monitoring

Monitoring for mealybugs has four components: Searching under bark, looking for honeydew and sooty mold, monitoring ant activity and pheromone

traps. Searching under bark for adults, nymphs and wax can be done any time of the year, but is most successful during the growing season. Look under loose bark at the base of spur positions and along the trunk. If mealybugs cannot be sighted first hand, the presence of the sticky honeydew and black sooty mold on leaves and shoots are an indication they are active.

Pheromone sticky traps attract males when they are in flight. The timing of flights varies by species and region. In general, traps should be monitored in the spring and late summer, and the identification of a flight in progress from elevated trap counts can be used to time mating disruption sprays. Male

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Office: 559-686-3833 Fax: 559-686-1453 2904 E. Oakdale Ave. | Tulare, CA 93274 newerafarmservice.com 28

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September / October 2020

VINEYARD REVIEW

Vine mealybug are the main mealybug species causing economic damage in California vineyards (photos courtesy Stephanie Bolton, Lodi Winegrape Commission.)

Mealybug themselves can cause economic damage to grape crops but also vector leafroll diseases, which can spread quickly within a vineyard and region.

mealybugs are extremely small and can only be identified using a dissecting scope.

and the incidence of virus to tolerable levels given time.

Another indirect way of monitoring for mealybugs is observing ant activity.

Argentine ants tend the mealybugs and collect the honeydew. If a large number of ants are visiting the vine it is likely mealybugs are present.

“If leafroll infected vines are at very low levels (probably around 0.5%, but dependent on the accepted risk), mealybug control using the more desirable biological control is feasible, as most mealybugs in such a vineyard are not viruliferous, and slightly higher levels of infestation can be tolerated,” said Pietersen. “This generally involves the augmentative release of mealybug predators and parasitoid,” he said.

The two major biological control agents on mealybugs are Anagyrus pseudococci and Cryptolaemus montrouzieri.

Anagyrus pseudococci is a parasite of the vine mealybug. It lays one egg per host in adult mealybugs. Parasitism rates can run from 20% to 90% depending on the region. The mealybug destroyer lady beetle (Cryptolaemus montrouzieri) is a predator of mealybugs, especially on egg sacs. Although found in most grape growing regions of California, mealybug destroyer populations are often augmented with releases of the insects purchased from an insectary. These two biological control agents (plus others) can dramatically reduce mealybug populations, although not below economic thresholds, by themselves.

Control Strategies

Growers have a suite of control measures they can bring to bear against mealybugs and virus. These include insecticides, biological control, mating disruption and the rogueing of infected vines. The choice of strategy varies depending on the severity of the mealybug infestation, the extent of virus infected vines, grower tolerance of both mealybugs and virus, and cost.

“If a vineyard contains a relatively high incidence of leafroll infected vines… it is essential to manage the levels of mealybugs to extremely low levels,” said Dr. Gerhard Pietersen of the Department of Genetics at the University of Stellenbosch. A high incidence of leafroll virus may be as low as 10% infected vines depending on mealybug density and the desire of the grower to halt its spread.

“This is because many of the mealybugs in that vineyard will be viruliferous (carry the virus) and can spread the virus to healthy vines,” he added.

Under these conditions, systemic insecticides are required. Used in combination with the rogueing of infected plants and biological control, it is possible to reduce mealybug densities

Biological Control

Insecticides

Three important insecticides for the control of mealybugs are Movento, Admire Pro and Applaud. Movento is spirotetramat. It is a systemic and may take four weeks before results are observed. The most efficacious September / October 2020

time to apply is bloom time. It is applied as a spray to the canopy. Admire Pro is an imidacloprid product applied to the soil around bloom time. This product works best when there is a second application 21 to 45 days after bloom. Applaud is a buprofezin, an insect growth regulator. It is best applied when crawler emergence is at its peak.

When these products are used in combination with each other and other insecticides such as Venom, Platinum or Belay, mealybug populations can be reduced to levels where biological control and mating disruption have a significant impact. Growers should rotate chemistries as much as feasible to avoid the development of resistance in the mealybug population to any one mode of action.

Mating Disruption

Mating disruption is the practice of spraying female sex pheromones into the vine canopy. This confuses the males and prevents mating. CheckMate VMB-F and CheckMate VMB-XL are pheromone products for vine mealybug. Sprays should be timed based on increased catches of male mealybugs in pheromone traps. It can be applied in 30-day intervals during the late spring to early fall depending on the Preharvest Interval (PHI).

Ant Control

High populations of Argentine ants (Linepithema humile) are associated with high populations of mealybugs.

Argentine ants interfere with biological control. Tilling the middles for weed control can destroy their nests and

Continued on Page 30 www.progressivecrop.com

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VINEYARD REVIEW

Continued from Page 29 reduce their attention to the mealybugs as they rebuild their nest. Cultivating in-row with an implement such as a French plow can also be effective.

Insecticides are best applied in a bait station, which require significant labor to distribute and maintain.

Vine Removal

Removing (or rogueing) a virus-infected vine is one way to reduce the spread of virus within the vineyard. Vines with red leaves should be flagged in the late summer when symptoms are the most dramatic. These vines should be removed as soon as possible after harvest for optimum control. Removing individual mature vines is difficult and expensive.

Areawide Pest Management Programs

In some areas of California, areawide pest management programs (AWPM) have been formed to address widespread infestations of mealybugs and similarly widespread incidence of GLRaV3. AWPMs are coordinated pest management activities over a large geographical area. The concept is that pest populations are not defined on a fieldby-field basis. Instead the population

of the pest is defined by the extent of contiguous hosts in space. This means the mealybugs in an area with contiguous vineyards need to be managed as uniformly as possible across properties.

Mating disruption is very effective when used as part of an areawide pest management program, for example. In Monterey County, this has taken the form of “pest management neighborhoods.”

“A pest management neighborhood is a group of growers who are physically proximal,” said Kim Stemler, Executive Director, Monterey County Vintners and Growers Association. “This proximity means that pests could easily be transported from one vineyard to another. Further, these vineyards are so close that their individual prevention and treatment strategies can be coordinated so that the net effect is mutually beneficial to all vineyards in the neighborhood.

“In Monterey County, the winegrowers defined the neighborhood boundaries and they meet regularly to share and coordinate prevention actions, what they are seeing in the vineyards, and their treatment strategies,” she added. “By working together in this way, there is a more effective and integrated cross-county approach to pest management.”

Stephanie L. Bolton, Research & Education Director/Sustainable Winegrowing Director of the Lodi Winegrape Commission, described a similar coordinated approach in the Lodi region.

Monitoring for mealybug is an essential part of the control program. Searching under loose bark at the base of spur positions and along the trunk for adults, nymphs and wax can be done any time of the year, but is most successful during the growing season.

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“As a region, we have been successfully using education and outreach—getting all growers to come together to understand why managing for mealybugs and viruses is important to their financial investment in the vineyard –and we’re fostering very open, collaborative sharing of management trials and tribulations with their costs,” she said.

As part of these efforts, the Lodi Winegrape Commission has promoted a suite of practices. “More specifically, in addition to typical mealybug IPM, we are incorporating extra scouting September / October 2020

(for mealybugs, beneficials, and virus symptoms), flagging and mapping mealybug hotspots and virus infections, virus testing, neighborhood communications, and most importantly the removal of leafroll-infected vines as it makes economic sense for each situation,” said Bolton.

She added, “The education and outreach has definitely been working—our growers know a lot more about mealybug management, especially biocontrol, and viruses now than they ever have before, and this helps them make more informed financial decisions about their vineyards.”

One example of the Lodi Winegrape Commission’s education and outreach activities is the What Every Grower Should Know: Viruses workbook which includes an extensive chapter on mealybug management. Taken together, these efforts have shown success at reducing mealybug densities in some vineyards in Lodi particularly through biological control and mating disruption.

Without control measures, the pest-disease complex of mealybugs and leafroll virus is devastating. Fortunately, a combination of biological control, insecticides and mating disruption can reduce mealybug populations to tolerable levels. Coordination of pest management activities between growers increases the likelihood of success.

Research on this topic is ongoing. As Bolton said, “We always welcome new affordable tools for the toolbox!”

References

Bolton, Stephanie. 2020. What Every Winegrower Should Know: Viruses. Lodi Winegrape Commission.

Daane, K.M. et al. 2006. New controls investigated for vine mealybug. California Agriculture 60(1):31-38.

Daane, K.M., A. Ledesma, and E. Belloli-Ramos. 2020.

In Season Drip and Foliar Insecticides for a Mealybug in Grapes, 2019.Arthropod Management Tests. 45(1).

Gutierrez, A.P. et al. 2008. Prospective evaluation of the biological control of vine mealybug: refuge effects and climate. Journal of Applied Ecology 45: 524–536.

Tsai, C.W. et al. 2008. Transmission of Grapevine leafroll virus, Fernandez, L., Bosco, D., Daane, K. M., and Almeida, R. P. P. 2008. Transmission of Grapevine leafroll-associated virus 3 by the vine mealybug (Planococcus ficus).

Phytopathology 98:1093-1098.

Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

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VINEYARD REVIEW

Autonomous Predictions of Vineyard Yield

Machine Learning Modeling of Remote Sensing and Historical Data Assist at the Block Level

By LUCA BRILLANTE | Assistant Professor, CSU Fresno

P

re-harvest yield assessment is a routine practice during the growing season in all vineyards of the world. Except for some minor innovations (e.g. stratified random sampling based on satellite-derived vigor maps,) the practice has never really changed.

The method is based on counting and weighing clusters by hand in different locations of the vineyard, and is not only time-consuming and costly but also imprecise. The number of locations that can be measured in this way is restricted, and this reduces the accuracy of estimations. The industrywide error associated with this method in the U.S. is estimated to ±10%, although this may range up to 20% or more in some years.

However, yield estimates by the site are subject to much larger error with respect to industrywide or regional data (~20 to 100%.) Accurate yield estimation by vineyard is extremely critical from a management and economical point of view; it is crucial for crop price negotiation, harvest logistics, batch processing, marketing decisions and precision viticulture approaches (e.g. selective harvest.) To be meaningful to growers, the estimation not only needs to be accurate but also done early in the season.

“

Prediction Models

Early-season yield estimations are crucial for production efficiency and profitability in grapevine as in all crops. It should not be a surprise that field crops such as corn or wheat have received consistent investments across the world for this purpose. Multiple yield prediction models are now available to field crop growers to the point that they have started to use multi-model ensembles (i.e. averaging predictions obtained through many different models) to achieve even greater accuracies. Process-based models are much less abundant in grapevine and only a few options exist. These models have been developed with the intent of studying grape growth behavior in silico, i.e. simulations to answer plant biology or physiology questions, and not to answer production issues, i.e. estimate yields. They are very demanding to calibrate, and hard to transfer and apply to large surfaces. The result is that grape growers do not currently have a performing model to estimate block yield.

Other approaches to solve this issue have been the development of sensors based on trellis tension or robots based on machine-vision algorithms. These

We have different methods of testing the reliability of the error and obtaining a measure of accuracy or performance of the machine-learning model in estimating the outcome.

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”

Luca Brillante is an Assistant Professor at CSU Fresno specializing in precision agriculture (photo courtesy L. Brillante.)

robots, although very interesting and worth exploring, have demonstrated little applicability in real vineyards or over large surfaces for multiple reasons (price, excessively heavy datasets, low prediction performances, etc.) Machine vision is limited to what is directly visible, and grapes are often out of sight as they are located beyond several layers of leaves, especially in sprawling canopies. Furthermore, these approaches need highly skilled workers to manage the system and analyze the data.

Machine Learning Technologies

The use of machine learning to predict yields from remote sensing data and historical yield series is very recently emerging in field crops and promises to be the most suitable tool for large surface predictions. It has never been attempted at the block level or in specialty crops. Machine-learning algorithms are a class of very powerful statistical approaches for prediction purposes, fueling the artificial intelligence revo-

Continued on Page 34

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VINEYARD REVIEW

model are collected in a dataset called a training dataset. Within this dataset, we know the true outcome for each set of predictors; for example, the yield and weather data in a given year.

A computer will generally be able to well-relate the predictors to the outcome in the training dataset as it can see the two sides: The set of predictors and the corresponding outcome. Our goal is to see if these relationships are strong enough to also apply to new cases. In other words, if given a new set of predictors (weather data in a new year, or a new block,) we can predict the outcome (the yield in that year.)

Figure 1. Soil wetness index over the 200-acre ranch used in the dataset obtained from elaboration of the digital elevation model.

Continued from Page 32 lution in many information technology domains and recently also in agriculture. In my previous works on the use of these models in viticulture, they have been proven useful to predict leaf water potentials from weather and soil data, transpirable soil water from soil electrical resistivity and physical-chemical properties, map regions of water uptake by grapevine within heterogeneous soil profiles, and total flavonoid

content from texture characteristics of grape berries.

In machine learning, we teach a computer to learn from observations, i.e. the data. Learning means finding relationships between a set of variables that can be easily measured (such as weather data,) called a predictor, and the outcome we want to predict, which is a variable that is hard to measure or acquire (such as the yield.) The observations we use to develop or train the

We have different methods of testing the reliability of the error and obtaining a measure of accuracy or performance of the machine-learning model in estimating the outcome. One is building a test set, such as pulling aside a set of observations; we do not include those in the training set, but just use them to assess the accuracy of the machine. Another one is based on resampling strategies (e.g. cross-validation, bootstrap) and using the same principle, i.e. pulling aside some of the data only for assessing the accuracy.

The difference with the test set is that, in this case, the data after estimation are included in the training dataset

Figure 2. Error in model predictions on unseen data estimated through hv cross-validation (2a) or test set (2b). The performance of the training set was RMSE = 0.22 tons/acre, R2= 0.98. RMSE is Root Mean Square Error. The blue line is a linear regression and the black line is the identity line. The distance of the point from the line indicates the error for that observation. Predictions are obtained in July, two months before harvest.

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VINEYARD REVIEW

and the approach is repeated so that all data are used both for training and testing.

Very recent advances in machine-learning technologies were applied to the yield estimation problem in grapevine for the first time with this project. The model was developed from a historical series of yield data at the block level (i.e. truck weights), and publicly available satellite images, soil and weather data. Data were obtained from a 200-acre ranch in California over 16 years (13 yieldings) from planting of the first block in the ranch (Figure 1, see page 34). Complexity in the dataset was increased by great variability in the ages of blocks, in turn affecting yield variability because the ranch was not planted all at once. Also, four different varieties were represented (Cabernet-Sauvignon, Cabernet Franc, Petit-Verdot and Merlot Noir) on different rootstocks.

The yield was predicted at the block level (i.e. from growers’ data, using truck weights at harvest.) Predictors (also called features, explanatory or independent variables) such as weather and soil data, multispectral satellite images and cultural characteristics of the block were collected from publicly available CIMIS, USGS and NASA data. Retrospective satellite images derived from the Landsat series were quality filtered, atmospherically and topographically corrected, then used to compute multispectral indices (e.g.

NDVI, etc.) of block vineyards with a fifteen-day schedule.

Estimation Results

The machine-learning modeling used was an ensemble of random forests and extreme boosting machines. The machine was trained and tuned; recursive feature selection was performed (consisting of selecting the most important variables to predict the yield within the whole dataset.) Evaluation of prediction performances was carried out rigorously in multiple ways to un-

derstand the limits of the approach.

The machine was able to learn all the information contained in the training dataset, root mean square error (RMSE) on the training dataset was equal to 0.22 tons/acre (0.54 tons/ ha), R 2 = 0.98. Because of the limited size of the dataset, slowing down the overfitting process was key to ensur-

ing the transferability of the model to estimations in unseen conditions (new blocks/vintages) as evaluated in the following tests. Estimation of errors on unseen observations was first obtained through hv cross-validation, a form of cross-validation for time series where

Continued on Page 36

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VINEYARD REVIEW

MONTH (Data from January to...)

RMSE (tons/acre)

R2

May

1.0

0.21

June

0.69

0.43

July

0.72

0.5

Table 1. Errors associated with estimations obtained at different times during the season. The model only used predictor data from January to May, or June or July.

Continued from Page 35 the training set and the validation set are obtained from different years. This is a more realistic estimate of model performances on future data, RMSE = 1 tons/acre (2.4 tons/ha) (See Figure 2a, see page 34).

To test the approach in real conditions, the model was developed using only the first 10 years of available data and using the last three as test sets, then following the approach in Figure 2, see page 34. In other words, the model was trained as the user was standing in year 13 of ranch life, having access to all previous years of yield data but with the problem of estimating the harvest of year 14 (yet to come), then continuing for the following two years (14 and 16). This is a very realistic error estimate of model performances for these last three years: RMSE= 0.72 tons/acre (1.8 tons/ha), R 2= 0.5, (Figure 2b, see page 34). To assess the transferability of the model to new blocks, all the data obtained from one block were removed, the model was fitted on the data from the remaining blocks and the model was used to predict the blocks left aside (leave-one-block out validation.) The procedure was repeated for all blocks in the dataset having at least 10 years of observations, and the model showed satisfactory performances, RMSE = 1.1 36

Progressive Crop Consultant

tons/acre, R 2 = 0.68 on predicting yield from never observed blocks.

This also means that the model would improve the performances when some yield data from the current vintage are included in the learning set (i.e. when harvest starts.) This preliminary data did not allow to reliably estimate the performances of the model on anomalous years having very low or high yield, meaning an average difference of >50% with respect to the all-year average. The reason was that these years were not well-represented in the dataset (only one low year and one high year.) If these years were removed from the dataset and used for error estimation (as test set), the machine would not have had any possibility to learn about data in these ranges (in statistics this is commonly defined as an extrapolation error in model prediction.) This issue can only be solved by increasing dataset size so that more anomalous vintages are part of the learning set. For practical use, a warning can be issued to the user, informing when predictor data lie outside the observed range of values within the model, and to take additional caution.

With successive learning cycles, enlarging the range of observations would also allow the model to learn how to predict extraordinary years.

September / October 2020

How early could yield estimations be obtained? To answer this question, the machine was trained to predict yields using only data from January until May, then until June and July (moving in the inner cycle in Figure 2), i.e. simulating the model did not have access to data from later months. The error was estimated on the test set from the last three years. These results are reported in Table 1. The error decreases getting closer to harvest and is lower in June and July with respect to May. In conclusion, using machine learning to predict yield in vineyards, especially in areas where the crop is not adjusted (no fruit is dropped,) has the potential to deliver an estimate that can be autonomously acquired, although it risks being hard to obtain very low error estimates. This can be an additional tool to simplify the current process.

Effectiveness is important to build a very large training dataset, or else the machine will have little capability to effectively scale up to new locations or years. Large corporations may build this alone; smaller growers need to share data as building this at the ranch scale risks being ineffective.

Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

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VINEYARD REVIEW

Chemical and Biological Control of Nematodes Affecting Grapes in the San Joaquin Valley

By GABRIEL TORRES | UCCE Farm Advisor, Tulare County and ELIZABETH FICHTNER | UCCE Farm Advisor, Tulare County

I

n vineyard systems, nematodes are pests that parasitize roots, causing loss of vine vigor that may lead to mortality. At an ecological level, however, nematodes occupy diverse habitats, serving as free-living organisms in water and soils, and as both plant and animal parasites. These microscopic roundworms (See Figure 1) may be associated with both plant and veterinary diseases, as well as human diseases. In

some agricultural systems, nematodes may serve as indirect elicitors of plant disease, either by serving as the vector of a plant virus (i.e. grapevine fanleaf virus,) or by predisposing plants to infection by other pathogens (i.e. bacterial canker on Prunus sp.)

Plant parasitic nematodes are the only animals known to cause plant disease.

Although there are numerous vertebrate animals that serve as pests on Beat the Heat & Care agricultural and for Your Crops with: horticultural crops, nematodes are classified as pathogens because their dam® age results from a continuous process Frost & Freeze and not Additional Environmental Stress Conditions that the product is useful for: an event.

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Progressive Crop Consultant

Nematode Species and Management

Like other plant pathogens, individual nematode species may have either a wide host range, inducing disease on many crops, or a narrow host range, affecting few hosts. For example, the citrus nematode (Tylechulus semipenetrans) has a narrow host range. Conversely,

September / October 2020

Figure 1. Ring nematode (Mesocriconema xenoplax) (Photo courtesy Zin Thu Zar Maung, UC Riverside.)

root knot nematode (Meloidogyne spp.) infects more than 150 plant species including grapes. Crops susceptible to multiple nematode species may be concurrently predated upon by more than one nematode species. In perennial cropping systems, concurrent host predation by multiple nematode species is common and may result in exacerbated symptom development than would otherwise be observed by infection with an individual nematode species.

Among the 22 genera of plant-parasitic nematodes identified to date, only 10 have been reported to infect grapevines.

The most relevant species affecting grape production in California are Rootknot (Meloidogine spp.), citrus nematode, lesion nematode (Pratylenchus spp.), dagger nematode (Xiphinema spp) and ring nematode (Mesocriconema xenoplax).

Nematode management can be divided into two complementary categories: preplant and postplant strategies. Preplant management strategies are designed to reduce the initial population of plant parasitic nematodes at planting as well as suppress future population growth of plant parasitic nematodes. These strategies include soil fumigation, anaerobic soil disinfestation (ASD), the planting of nematode-free nursery stock, and selection of nematode resistant or tolerant rootstock (Figure 2, see page 39.) Postplant nematode management strategies are generally limited due to the need to protect and facilitate growth of the crop.

VINEYARD REVIEW Table 1. Seasonal nematode populations in grape vines3.

­

as well as cultural practices to prevent introduction of nematodes from infested fields. Nematodes can be moved to uninfested sites on contaminated equipment or in irrigation or drainage water.

Preplant Treatment Options

Prior to planting, a grower may evaluate risk of nematode damage by taking soil samples for nematode analysis and Figure 2. Grape rootstocks susceptible to nematodes exhibit reduced considering root mass and presence of galls (left) in comparison to resistant rootwhether the stocks (right) (Photos by G. Torres.) prior crop and upcoming crop are shared Postplant management tools include hosts for any common nematode species. applications of biological and chemical Preplant soil sampling for nematodes compounds for nematode management, will provide an estimate of the nemaSeptember / October 2020

tode population in the soil before planting. After planting, nematode sampling is recommended every three to five years to track changes. If preplant soil sampling determines a plot to be free of plant-parasitic nematodes, measures should be taken to prevent introduction of the parasites to the site. Such measures include the use of nematode-free certified plants from the nursery and the use of sanitized equipment to prevent nematode introduction to the site.

However, if pre-plant sampling indicates plant parasitic nematodes to be above threshold levels, a grower can evaluate the need for preplant soil treatments such as fumigation or ASD. Table 1 illustrates the critical nematode population levels for multiple nematode species affecting grapes.

ASD is a preplant soil treatment option that serves as an alternative to fumigation. Its application to soil disinfestation arose from years of research designed to identify alternatives to methyl bromide and reduce greenhouse gas emissions.

ASD consists of the incorporation of organic matter into soil followed by soil saturation. ASD activates the soil microbial community, resulting in accelerated growth of the microbial population. The accelerated microbial activity combined with the saturated environment transforms the soil to an anaerobic state.

While anaerobic, the depleted oxygen is detrimental to organisms such as nematodes, fungi and some bacteria and plants. Fumigants also have a biocidal activity against a wide range of organisms, but their use is limited by costs and environmental regulations.

Nematode-resistant rootstocks are of value in soils where nematodes are present, either from insufficient response to fumigation or ASD, or from the inability to integrate either soil treatment method prior to planting. The use of nematode-resistant rootstocks can also complement soil treatment techniques, thus mitigating the risk of developing higher nematode populations in the future and reducing the need for future biological or chemical inputs to

Continued on Page 40 www.progressivecrop.com

39

VINEYARD REVIEW Table 2. Rootstock resistance to different nematodes species in California. Adapted by Dr. Karl Lund from Ferris et al. 20134.

Genotype

M. incognita Race 3

M. javanica

Root-knot Nematode

Root-knot Nematode

Freedom

Very High

Very High

Harmony

Very High

Ramsey

Very High

Nematode Type

M. chitwoodi

X. index

X. americanum

M. xenoplax

P. vulnus

T. semipenetrans

Para. hamatus

Root-knot Nematode

Dagger Nematode

Dagger Nematode

Ring Nematode

Lesion Nematode

Citrus Nematode

Pin Nematode

Low

Medium

Low

Low

Very High

Medium

Medium

Medium

Very High

Low

Low

Medium

Low

Low

Very High

Low

Low

High

Low

Low

Very High

Low

High

Low Low

1103Paulsen

Meloidogyne pathotypes Harmony A&C Root-knot Nematode Low

Low

High

Low

Low

Low

Medium

Medium

Low

Riparia Gloire RS-3

Very High

Very High

High

High

Low

Low

High

RS-9

Very High

Very High

Very High

Very High

Low

Low

Medium

Low

Low

Low

Medium

Medium

St. George

Very High

Low Low

Low

Low

Teleki 5C

Medium

High

Low

Medium

Low

Low

USDA 1017A

Very High

Very High

Very High

Very High

Very High

High

Low

Medium

Very High

Very High

Medium

USDA 1023B

Very High

Very High

Very High

Very High

Very High

High

Very High

Very High

UCD GRN2

Very High

Very High

Very High

Medium

High

Medium

UCD GRN3

Very High

Very High

Very High

High

High

High

High

UCD GRN4

Very High

Very High

Very High

High

High

High

Medium

High

Continued from Page 39 the vineyard. A list of different nematode-resistant rootstocks available in California are presented in Table 2.

Postplant Options

Chemical and biological management strategies are the only techniques available after planting. Once the vineyard is planted, the use of fumigants, ASD and rootstock selection are no longer considerations for nematode management.

In California, the only chemical options registered on grapes are the active ingredients spirotetramat and imidacloprid.

Azadirachtin, Margosa oil, Myrothecium verrucaria, Purpureocillium lilaciunum and Quillaja are registered as biological controls. Once nematode populations are established, frequent monitoring of nematode populations is essential to evaluate both the biological and economical influence of chemical and/ or biological applications for nematode management.

Chemical applications are more effective when applied between budbreak and pre-bloom, or after harvest when the leaves are still active. Chemical applications during other phenological plant stages could result in reduced treatment efficacy. Because the two nematicides registered in grapes are also utilized as 40

Progressive Crop Consultant

insecticides for mealy bugs and other pests, the potential for pest populations to develop resistance to these products remains a possibility. Consequently, these active ingredients should be rotated and used in conjunction with other cultural practices to prolong product efficacy.

While synthetic chemical controls may only be applied once or, at most twice, in a season, biologicals may require more frequent applications. The use of two different biological modes of action is advised to enhance control1,2. Application by drip chemigation is preferred when allowed by local authorities and the manufacturer2.

Mitigation of abiotic stress on the crop is another factor facilitating productivity in nematode-affected vineyards in both organic and conventional farming systems. Balanced nutrition and proper irrigation programs are also important to support plants affected by nematodes.

Improvement of soil microbial activity and diversity may be suppressive to plant parasitic nematode populations, and may promote populations of free-living nematode species that are not harmful to the plants.

September / October 2020

If you have questions, please contact your local farm advisor or your PCA. It is our best interest as advisors that you have a safe and productive growing season.

References

1) Hallmann J, Kiewnick S. Diseases caused by Nematodes in Organic Agriculture. In: Finckh MR, van Bruggen AH, Tamm L, eds. Plant Diseases and Their Management in Organic Agricultuture. 1st ed. St. Paul - Minnesota, USA.: APS press; 2015:91-105.

2) Zasada IA, Ferris H. Nematode Management. In: Wilcox WF, Gubler WD, Uyemoto JK, eds. Compendium of Grape Diseases. 2nd ed. St Paul, Minnesota, USA.: APS press; 2017:144-146.

3) McKenry M V., Bettiga LJ. Nematodes. In: Bettiga LJ, ed. Grape Pest Management. 3rd ed. DAvis: UCANR; 2013:449-470.

4) Ferris H, Zheng L, Walker MA. Resistance of Grape Rootstocks to Plant-parasitic Nematodes. J Nematol.

2012;44(4):377-386.

Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

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VINEYARD REVIEW

GRAPE BERRY RIPENING AND PREHARVEST MANAGEMENT

By GEORGE ZHUANG | UCCE Viticulture Farm Advisor, Fresno County

Severe sunburn on Syrah wine grape.

V

eraison is the most critical phenological stage of grape growing. At veraison, berries change color from green to red/purple for red cultivars and sugar starts accumulating rapidly while organic acids decline simultaneously with other flavor com-

pounds changing as well. After veraison, growers can expect to harvest the fruits soon after a whole season’s effort.

However, the window between veraison and harvest is important for growers to meet the production goal successfully at harvest.

Figure 1. Syrah berry anthocyanin accumulation relative to Brix from the south and north side of the canopy after the onset of veraison until the 2019 harvest. At the same Brix, berry anthocyanins are higher on the north canopy than the south canopy.

42

Progressive Crop Consultant

September / October 2020

Berry Chemical Change

The biggest berry chemical change after veraison is the increase of sugar with the simultaneous decrease of organic acids with fruit pH rising near the harvest. Fruit sugar content, usually measured by Brix, is often targeted by wineries for the certain wine program, and a minimal Brix is usually required for the harvest.

However, color might be the most visible change at veraison for red grape cultivars, mainly because the anthocyanins start to accumulate at the skin of the grape berry after the onset of veraison, although teinturier cultivars (e.g. Rubired) accumulate anthocyanins in both skin and pulp. Anthocyanin typically increases as sugar accumulates, and its content can be affected by cluster light exposure, irrigation scheduling, crop management, vine nutrition and pest/disease. In the San Joaquin Valley, extreme heat events usually cause berry sunburn and lead to the reduction of berry anthocyanins at harvest. Less berry anthocyanins at the sun-exposed canopy are resulted from overexposure to light and excessive heat load (Figure 1). Therefore, there are some critical tips which growers need to check before the harvest starts.

VINEYARD REVIEW

Veraison of Cabernet Sauvignon wine grape cluster (all photos courtesy G. Zhuang.)

Irrigation Management

With expected heat events in the run up to September, growers should adjust their irrigation scheduling according to the local weather forecast. It is easy to use grapevine ET to schedule the weekly irrigation amount. Grape ET developed by Dr. Larry Williams from

Powdery mildew on Fiesta raisin grape.

UC Davis has been well-studied and proven to be suitable for SJV wine/ table/raisin grapes. Crop coefficient (Kc) developed by Williams based on growing degree days has been applied to the recently established crop ET reports. The crop ET reports have been created through DWR and UCCE,

and updated weekly on UCCE Fresno website (http://ucanr.edu/sites/viticulture-fresno/Irrigation_Scheduling/).

Raisin and wine grape ET information have been offered through the crop ET

September / October 2020

Continued on Page 44

www.progressivecrop.com

43

VINEYARD REVIEW

Bunch rot on Zinfandel wine grape.

Continued from Page 43 reports, and gallons per vine per week are available based on the pre-defined trellis type, planting density and irrigation efficiency. Growers should adjust the number from ET reports based on the water availability/quality, the desired stress level and the production goal.

Disease/Pest Management

It has been reported that powdery mildew pressure has been high this year, and the skin crack caused by powdery mildew could also lead to bunch rot close to the harvest. Timely spray, rotation of fungicides according to FRAC code and good coverage as well as water/nutrient and canopy management are the keys for successful PM management. UC Powdery Mildew Risk Index (http://ipm.ucanr.edu/calludt.cgi/ GRAPEPMVIEW1) is still a valuable tool for SJV growers to time sprays and reduce cost. It has been suggested to rotate different groups of fungicides to avoid building any potential fungicide resistance, and resistance has certainly become a concern for many growers. USDA ARS has been working with UCCE to offer fungicide resistance tests. Interested growers can contact UCCE local farm advisors for further information.

Calibrate your sprayer and check your nozzle to make sure it works properly. It is also recommended to check spray coverage by placing water-sensitive paper cards in the targeted zones and run the sprayer with water to confirm good coverage. One of the greatest challenges for PM control in SJV is water/nutrient management, and sometimes it can be easily overlooked. Dense canopy promoted by overwatering and excessive nutrients (e.g. N) can exacerbate the PM and make the good coverage difficult. Following grape ET reports to

44

Progressive Crop Consultant

guide irrigation scheduling not only saves water and increase yield/quality but helps the PM management as well. It has been suggested to manage nutrients, especially N, according to the water and grapevine tissue analysis to avoid overfertilizing the vines.

Sunburn/Heat Stress

Berry sunburn can be a severe problem resulting in pre-raisining and berry shrivel on certain varieties, and it can cause significant yield loss and quality compromise. With potential heat events occurring in August and September, sunburn prevention is important for growers to maintain yield and berry quality at harvest.

Water is the best arsenal in terms of sunburn/heat stress.

Proper irrigation based on ET reports and local experience is the most important way to make sure vines are not severely water-stressed during the hot days. Water stress coupled with heat waves can exacerbate sunburn and heat stress. Canopy management, including shade cloth and spray protectants, like kaolin and calcium carbonate, can also be used to reduce solar radiation and alleviate berry sunburn and vine heat stress.

Veraison is the critical phenological stage before harvest, and growers need to maintain healthy canopy and fruit to maximize yield and quality. Irrigation scheduling and disease/pest management, along with sunburn prevention, can be useful for growers to adjust their vineyard practices and achieve farm profitability.

Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

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Virtual Crop Consultant Conference Brings Experts and Consultants Together

P

rogressive Crop Consultant Magazine took its popular Crop Consultant Conference Virtual in September for a two-day interactive live event that featured some of the most prominent thought leaders in crop protection and nutrition, technology and crop management.

Co-hosted by PCC and the Western Region Certified Crop Advisers Association, the conference featured live presentations with audience participation through question and answer questions and attendee polling.

“I was very impressed with the quality of engagement we had between presenters at our two-day conference and the hundreds of crop consultants in attendance,” said Jason Scott, publisher and CEO of Progressive Crop Consultant Magazine.

“Obviously these virtual events are not a substitute for the live events, but the team at JCS Marketing worked hard to create an interactive experience that connected crop consultants with researchers, industry leaders and each other.”

Scott noted that the partnership with Western Region CCA helped the trade organization connect with its members in important ways as well.

Western Region CCA presented its first ever Crop Consultant of the Year Award to JW Lemons, national sales agronomist with SQM North America and a long-time leader in the industry and at WRCCA. In addition, the trade association for certified crop advisers in the west presented a number of scholarships to promising college students focused on becoming pest control advisors and crop advisers and academic mentors who are grooming the next generation of leaders in the crop consulting industry.

Among the highlights of this year’s Crop Consultant Conference:

Navel Orangeworm Mating Disruption Panel

Act, how to choose a good lab, how to get the best sample and other topics of interest to crop consultants who rely on nutrient lab analysis to make fertility recommendations.

In addition, John Allan of SQM North America provided an overview of common potassium sources for use in California agriculture, their differences and similarities, regulations and availability.

Pest Management

Steve Vasquez, technical viticulturist with Sun-Maid Growers of California, gave an overview of the powdery mildew epidemic of 2019 and the residual effects felt in this year’s crop, as well details about how to put together the best management program for powdery mildew in grapes that will keep growers ahead of the curve with this important disease.

The nut industry’s leading minds in navel orangeworm mating disruption in nut crops shared their thoughts on the future of mating disruption and what consultants can do to integrate mating disruption into navel orangeworm management programs and improve performance of the technology. The panel featured Brad Higbee of Trece, Abby Cox of Semios and Emily Symms of Suterra.

UC Riverside Plant Pathologist Hailing Jin shared research on the development of a new treatment for citrus greening that could help control the transmission of the HLB disease by the Asian citrus psyllid through the injection of a peptide into trees.

Avram Slovic, head of agriculture in Latin America for Invaio, shared the company’s plans to bring the novel treatment to market by 2023.

“I (was) very excited by the quality of the questions that came through in the Q and A session,” said Symmes.

Technology and Application

Plant Nutrition

Leaders from some of the state’s top labs discussed issues surround nutrient analysis, including looming deadlines for testing under regulations of the Sustainable Groundwater Management

Karl Wyant, Vice President of Ag Science at Heliae Agriculture presented a look at the current state of biologicals to help CCAs use their discerning talents to help their clients understand the different modes of action, uses and applications of agricultural biostimulants. Polling during the session, showed that the audience was

very interested in learning more about biostimulants and how they can be used to improve crop performance.

Steve Koike, director of TriCal Diagnostics, discussed the role of testing in ascertaining a correct diagnosis for plant viruses to help drive management decisions. Using the framework of Covid-19, Koike explained how plant viruses are transmitted and the best ways to prevent transmission of those viruses.

Alireeza Pourezza, assistant Agricultural UCCE Mechanization Specialist at UC Davis, shared a new prototype he is developing called the Spray Backstop to improve deposition into tree tops from air blast sprayer applications. The Spray Backstop is currently under development but has been shown in trials to improve deposition while also preventing spray drops from escaping the orchard canopy.

Another well attended talk related to crop management covered the

basics of tank mixing and avoiding potential hazards when deciding on the compatibility of products.

Chris Underwood, head of product development with Custom Agronomics, gave a throughout review of where people go wrong when mixing products in the tank.

Scott said JCS Marketing will continue to bring the industry’s brightest minds and hottest topics to crop consultants with plans to return to a live two-day

conference in Visalia, Calif. next September.

“Ideally we will be back to doing live events this time next year and will look forward to seeing our readers in person, again bringing crop consultants state-of-the-art information from the industry’s top researchers, suppliers and thought leaders that they can bring to their grower customers.”

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