Progressive Crop Consultant May/June 2022 by JCS Marketing, Inc.

May / June 2022 The Challenge with Aflatoxins in Pistachio and Almond Five Key Items on Your Vineyard Soil Report Mating Disruption of California Red Scale in Citrus

VINEYARD REVIEW Grapevine Water and Nutrient Management Tips During Drought Mechanization Improves Pruning Efficiency in Table Grape Vineyards Aspergillus Vine Canker: An Overlooked Canker Disease of Grapevine in California

Volume 7: Issue 3 Photo courtesy of T. Tian

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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

The Challenge in Management of Aflatoxins in Pistachio and Almond

CONTRIBUTING WRITERS & INDUSTRY SUPPORT

12 16 20

Molly Arreguin Department of Plant Pathology, UC Davis

Five Key Items to Look at on Your Vineyard Soil Report

Mating Disruption of California Red Scale in Citrus

Biosolarization: Returning Almond Hulls and Shells to the Orchard to Improve Soil and Almond Tree Health

26 32 36

Grapevine Water and Nutrient Management Tips During Drought

Themis Michailides Plant Pathologist, UC Davis/ Kearney Research and Extension Center

Rory Crowley Nicolaus Nut Company

Emily Shea UC Davis

Karina Elfar Department of Plant Pathology, UC Davis,

Christopher Simmons UC Davis

Akif Eskalen Department of Plant Pathology, UC Davis

James J. Stapleton Kearney Agricultural Research and Extension Center

Matthew Fidelibus Extension Viticulturist, UC Davis

Emily J. Symmes Ph.D., Senior Manager of Technical Field Services, Suterra

Ramon Jaime Project Scientist, UC Davis/ Kearney Research and Extension Center Vern Johnson CCA/PCA, President, Arizona Ag Solutions, PLLC

Tian Tian UCCE Viticulture Farm Advisor, Kern County George Zhuang UCCE Viticulture Farm Advisor, Fresno County

UC COOPERATIVE EXTENSION ADVISORY BOARD Surendra Dara

Steven Koike Tri-Cal Diagnostics

Kevin Day

UCCE Integrated Pest Management Advisor, Stanislaus County

Director, North Willamette Research and Extension Center UCCE Pomology Farm Advisor, Tulare and Kings Counties

Mechanization Improves Pruning Efficiency in Table Grape Vineyards

Aspergillus Vine Canker: An Overlooked Canker Disease of Grapevine in California

Marcelo Bustamante Department of Plant Pathology, UC Davis

Amanda Hondson UC Davis

VINEYARD REVIEW

Tate Lone UC Davis

Elizabeth Fichtner UCCE Farm Advisor, Kings and Tulare Counties

Jhalendra Rijal

Mohammad Yaghmour

UCCE Area Orchard Systems Advisor, Kern County

Katherine Jarvis-Shean UCCE Orchard Systems Advisor, Sacramento, Solano and Yolo Counties

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.

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The Challenge in Management of Aflatoxins in Pistachio and Almond

Figu Achi aflat split proc

By THEMIS MICHAILIDES | Plant Pathologist, and RAMON JAIME | Project Scientist, UC Davis/Kearney Research and Extension Center

(additional authors at the end of the article.)

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Figure 1. (A,B) Early split pistachios serve as the “Achilles Heel” for navel orangeworm infestation and aflatoxin contamination. (C) Suture staining of early split that helps their removal in the sorting belt at the processor. 40

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> 0.0 ppb > 10 ppb > 100 ppb

30 20 10 0

0-0.5 0.5-1.0 1.0-2.0 >2.0 Navel orangeworm (%)

Figure 2. Effect of level of navel orangeworm damage to aflatoxin contamination Aflatoxin B1 (log ng/sample)

flatoxins are a category of almonds for direct consumption. The mycotoxins, which are toxic tolerances are even stricter for walnuts compounds produced by fungi and dried fruit (4 and 2 ppb for toral (Myco= µύκης, which means fungus in and B1 aflatoxins, respectively), and for Greek.) So, aflatoxins are toxins prodried figs, total aflatoxins are 10 ppb duced by specific types of fungi. These while for B1 is 6 ppb. compounds are by-products (secondary metabolites) produced mainly by Because of these strict tolerance threshtwo fungal species, Aspergillus flavus olds, the U.S. (and to a lesser degree and Aspergillus parasiticus, which are other countries that produce and marpresent in California nut crops and fig ket products susceptible to aflatoxins) orchards when they grow in susceptible takes extraordinary measures to reduce substrates. These compounds are very this contamination as much as possible. toxic, carcinogenic and cause disease when consumed in large amounts. Early Aflatoxin Research Because of the high toxicity, aflatoxins For a decade (1991 to 2001), the reare regulated worldwide by governsearch in our plant pathology laboments, dealing with marketing products ratory focused on cultural practices susceptible to contamination with these and reduction of damage by the navel mycotoxins. There are several kinds of orangeworm (NOW) to reduce aflatoxaflatoxins, such as B1 and B2, produced in contamination in almond and pistaby the above Aspergillus species. In adchio. For instance, in early research on dition, the latter species produces two pistachio, we discovered that the early more kinds of aflatoxins, G1 and G2. split (ES) nuts (Figure 1) serve as the The letters “B” stands for the blue color “Achilles Heel” for infestation by NOW that these compounds show and the “G” and infection by aflatoxigenic fungi, for the green color when contaminated leading to aflatoxin contamination. products are placed under a UV light (365 nm wavelength). In fact, when samples were collected from several orchards and separated In the U.S., the tolerance for aflainto ES without NOW damage, ES with toxins is 20 ppb (1 part per billion NOW-damaged nuts and normal nuts =0.000000001 gr). In the European (mature nuts but having hulls intact) Union (EU), for all (total) aflatoxin, the and analyzed for aflatoxins the results tolerance is 10 ppb while for B1 is 8 ppb, showed that ES contribute a lot in and these values are for pistachios and Continued on Page 6

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5 4 3 2 1 0 0

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Figure 3.Effect of feeding damage by navel orangeworm to aflatoxin accumulation (laboratory experiment with almonds)

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Continued from Page 4 aflatoxin contamination of pistachio as follows: ES (shriveled, i.e., those that had developed early and infested by NOW) had an average of 84% of the total aflatoxins in these samples; if one includes the ES with no NOW infestation, the total levels of the aflatoxins could explain 99.9% of aflatoxins in these samples. Although 20% of the samples represented ES that developed close to harvest had aflatoxins, the levels were only 2 ppb, representing only 0.1% of the total aflatoxins.

Aspergillus flavus

Aflatoxins:

Aspergillus parasiticus

B1, B2,

Aflatoxins:

B1, B2, G1, G2,

AF36 AF36(%) (%)

These results made us investigate ways The two aflatoxigenic species that occur in nut California tree nut Figure 4. Figure The two4. aflatoxigenic mold speciesmold that occur in California tree orchards to reduce the incidence of ES and also Inset: spores produced on “heads” conidiophores of the fungi. orchard. methods to reduce NOW damage. Normal mature nuts had no aflatoxins in these samples. The results were very consistent in two consecutive years. The AF36displaced displacedthe thetoxigenic toxigenic A. The AF36 A.flavus flavusisolates isolatesin insoil soil Moreover, when samples were collected and were separated based on their 90-95% 100 a 100 levels of NOW damage, we showed a !"#$%&'3)' K.4.37& a AF36 product that as the level of damage increased, 3.8*&'$)7. Untreated so did the aflatoxin contamination 80 80 frequency and amounts (Figure 2, see a page 4). Similarly in almonds, as the feeding sites caused by the NOW larvae 60 60 increased on almond kernels, so did a the aflatoxin levels (Figure 3, see page = Applic. of AF36 40 40 4). Therefore, it is obvious reducing the b damage by NOW will result in lower b risk for aflatoxin contamination, and b 20 20 b this is accomplished by doing sanitab tion (“mummy shake”) in both almond ns and pistachio. Avoiding water stress is 00 2009 2008 2009 2010 2011 another approach to reduce susceptibil2011 2008 2010 Year Year ity of trees to aflatoxin contamination. Specifically in pistachio, water stress in Figure 5. Very high displacement of toxigenic strains by the applied atoxigenic early season (May) increases the inciAF36 strain of Aspergillus flavus in commercial pistachio orchards during 2008 to 2011 dence of ES, and thus increases the risk when the Experimental Use Permit was for aflatoxin contamination.

Biological Control

Because aflatoxin contamination is very sporadic, and because there are no fungicides that would affect aflatoxin contamination, several countries now emphasize a biological control approach by displacing the toxigenic strains of A. flavus and A. parasiticus with the use of atoxigenic strains that are applied directly on to the orchard floor. In California, in cooperation with Dr.

Peter Cotty (USDA-ARS), the A. flavus AF36 strain was registered first in 2012 for use in pistachio and then the same product as AF36 Prevail® in 2017 for use in pistachio, almond and figs. As of August 2021, a second product using a different atoxigenic strain, Afla-Guard® GR manufactured by Syngenta Crop Protection, LLC, was registered for use in almond and pistachio. Pistachio and

almond growers can use either product starting in the 2022 growing season. But before moving into the application of either of these products, we need to provide a brief background into the history how this technology had developed over many years of research and the various challenges orchardists have experienced over the years in using the

Continued on Page 8 6

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AF36 and/or the AF36 Prevail products.

Reduction pistachiosamples samples Reduction in in aflatoxin-contaminated aflatoxin-contaminated pistachio after treatingwith withAF36 AF36biocontrol biocontrol after treating Reductionofofcontaminated contaminated samples Reduction samples(%) (%)

Continued from Page 6

As mentioned earlier, there are two major fungi that can produce aflatoxin and contaminate the susceptible crops, A. flavus and A. parasiticus. The A. flavus produces two strains in the soil based on the size of the sclerotia (resistant, survival structures), the S strain and the L strain (Figure 4, see page 6). All the isolates of the S strain are toxigenic, while among the isolates of the L strain, there are strains that produce various levels of aflatoxins and others not producing any strains. These latter strains are called atoxigenic.

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44.9% 38.6%

40 40

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39.9%

36.7%

30 30 20.4%

20 20 10 10

2008 2008 2009 2009 2010 2010

2011 2011 2008-2011 2008-2011 (4 years average)

First Harvest: An average of 40% reduction

(Doster et al. (2014), Plant Disease 98:948-956)

Figure 6. Reduction of aflatoxin- contaminated samples after application of AF36 atoxigenic strain during 2008 to 2011.

Figure 7. Reduced levels of displacement of toxigenic strains during 2012 to 2018 after application of AF36 atoxigenic strain in commercial pistachio orchards.

100

A. flavus AF36 (%)

All the strains of A. parasiticus are aflatoxin producers. An atoxigenic strain called AF36 was found to be among the most frequently encountered atoxigenic strains ranging in incidence from 4% to 12% while other groups of atoxigenic strains ranged from <1% to 2% among the strains in the soil. This strain was determined to be the same that was isolated earlier in Arizona from cotton fields and used there as a biological control agent to reduce aflatoxin contamination in cotton and corn. Therefore, since all the toxicological studies were done by USDA and because the AF36 was the one most frequently encountered in California tree nut and fig orchards, we selected and used it as a biological control

P value =0.0033

50 50

80 60

a ab

40 20

Untreated AF36 2008-11 AF36 2012-18

Untreated

2012

2013

a Treated

Last treated till 2011

2014

2015

2016

Year

a a b

2017

Displacement 50-70%

2018

Figure 7. Reduced levels of displacement of toxigenic strains during 2012 to 2018 after application of AF36 atoxigenic strain in commercial pistachio orchards.

agent in the Kearney experimental orchards first to measure displacement of the toxigenic strains. After 10 years of research in microplots initially and three years as an Experimental Use Permit compound used in 3,000 acres of pistachio, eventually, the AF36 strain was registered for use in pistachio orchards in 2012. The initial carrier of the strain was wheat seed inoculated in big fermenters with the A. flavus AF36 strain. Five years later, the manufacturer was able to register the AF36 Prevail® product, which contains the same AF36 strain and uses sorghum as the carrier, the surface of which is coated with propagules of the atoxigenic strain via a polymer. Recently, a second atoxigenic strain, Afla-Guard GR, was provisionally registered for use in pistachio and almond. There is also an interest now by the walnut and fig industries to have both these products registered for these crops.

Challenges

When experiments using the atoxigenic strain AF36 were initiated in 2002, we determined a very high displacement ability of the toxigenic strains in the soil of microplots, which reached almost to 95% displacement at the end of the fourth year, applied once per year. When the EUP was granted in 2008 and 3,000 acres of pistachio were treated with AF36 once per year, the displacement also reached to 95% by the fourth year of application (Figure 5, see page 6). It was during this time when analyses of first harvest pistachio library samples showed a 40% reduction in aflatoxin-positive samples and an almost 55% reduction in aflatoxin-positive library samples of the second harvest (or reshakes) (Figure 6, see page 8). During 2012 to 2019 and after application of the product yearly, we noticed a lower percentage of displacement that ranged from 50% to 70% (Figure 7, see page 8). The blocks that were treated last in 2011 showed a continuous decrease of displacement from 65% down to about 30%, which remained

stable from 2015 to 2017, but there was a jump to almost 50% in 2018 (Figure 7, see page 8). The untreated fields ranged from about 32% to 20% during this period (2012 to 2018). During the same seven-year period, when library pistachio samples were analyzed for aflatoxins, only in two years (2013 and 2017) were there major reduction level in aflatoxin-positive samples, while in the remaining years, the reductions in

positive samples were very small, ranging from 5% to 30%, and in some years (2014 and 2016), there was no reduction at all (Figure 8, see page 10). To overcome these challenges and to minimize the influence of treated orchards with AF36 Prevail® by toxigenic propagules (spores) escaping non-treat-

Continued on Page 10

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Figure 8. Following the EUP years, reduction of aflatoxin positives ranged from 0% - 85%; but during 2016-2019 this reduction was only 0% -30%. 100 406

80 135

Reduction (%)

ed orchards, we initiated research projects funded by both the pistachio and almond industries on long-term areawide projects. The rationale was that when large area is treated year after year, the influence by non-treated orchards should be minimal. By doing this, we were able to increase the levels of displacement from about 45% in almond and about 65% in pistachio to 80% in almond and 95% in pistachio (Figure 9). This is a significant increase in the levels of displacement of toxigenic strains and we expect now to significantly reduce the levels of aflatoxin-positive samples. A good example for displacement of toxigenic strains is from our research with almonds, where toxigenic strains ranged from 65% to 83% before treatment with AF36 Prevail to about 25% toxigenic Aspergillus in fields treated, while the untreated orchard maintained an incidence of 68% of the toxigenic Aspergillus strains. In the treated orchards, the atoxigenic strains reached a level of about 80% as measured at harvest time. (Figure 10).

333 365 209

71 425

NOW DAMAGE

279

242

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019

Figure 8. Following the EUP years, reduction of aflatoxin positives ranged from 0% to 85%; but during 2016-19 this reduction was only 0% to 30%.

Figure 9. Effect of area-wide, long-term treatment with AF36 Prevail atoxigenic strain on the displacement of toxigenic strains in almond and pistachio commercial orchards.

120 100

Strains from Aspergillus Flavi Atoxigenic A. flavus AF36 All toxigenic strains

Displacement 75 - 95%

80 60 40 20

The new biological product, Afla-Guard GR is now registered and will be available to pistachio and almond growers to use commercially in 2022. The active ingredient of Afla-Guard GR is the NRRL 21882 Aspergillus flavus strain and the carrier is barley seed. In contrast to AF36 Prevail that is sorghum seeds coated with the spores of AF36 strain of A. flavus, the NRRL 21882 strain is inoculated in the barley seed, i.e., the entire barley seed kernels are “infected” (colonized) by the latter strain. The Afla-Guard GR product sporulated at higher rates under lower temperatures and lower soil moisture than the sporulation produced by AF36 Prevail when the two strains were compared side by side and under the same conditions. However, since we do not have any results from aflatoxin analyses of pistachio samples, it is still unknown how this product will perform under commercial application. The efficacy of each AF36 Prevail and Afla-Guard GR will be studied in side-byside commercial fields this year for the first time.

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457 391

415

Moving Forward

Percent of isolates

Continued from Page 9

Almond Pistachio Almond Pistachio Not Treated Area Treated Area

Figure 9. Effect of area-wide, long-term treatment with AF36 Prevail atoxigenic strain on the displacement of toxigenic strains in almond and pistachio commercial orchards. Figure 10. Effect of area-wide, long-term treatment with AF36 Prevail atoxigenic strain in displacement of toxigenic strains in commercial almond orchards

Before treament

Treated

80% displacement

60% reduction of toxigenic strains

Figure 10. The effect of area-wide, long-term treatment with AF36 Prevail atoxigenic strain in displacement of toxigenic strains in commercial almond orchards.

May / June 2022

In addition, we are doing studies to overcome other challenges with the commercial application of these products, such as managing predation by ants, rodents and birds, the negative effect of the direct sunlight on the seed inoculum under very high temperatures, the coordination of irrigation either just before or immediately after applying the biocontrol product, etc. All of these are challenges that can differ from orchard to orchard and therefore may affect variably the efficacy of the biocontrol products. (Co-Authors of this article include: Mark Doster, Plant Pathologist, Pummi Singh, Post-Doctoral Research Associate, Giuseppe Fiore, Graduate Student, University of Bari, Italy, Victor M. Gabri, Staff Research Associate and Graduate Student, Yong Luo, Project Scientist, Ryan Puckett, Greenhouse/ Cold Room/Physical Plant Officer and Laboratory Assistant, and Apostolos Papagelis, Agronomist, University of Athens, Greece, John Lake, Laboratory Assistant. All personnel are affiliated presently with UC Davis/Kearney Ag Research and Extension Center, Parlier, Calif. 93648.) We thank the California Pistachio Research Board and the Almond Board of California (Food Quality and Safety Committee) for funding this research. Also, funding was provided by the USDA/Aflatoxin Elimination Technical Committee and the CDFA/Grant 16-SCBGP-CA-0035. Especially, we acknowledge the extraordinary support of Wonderful Orchards Company, which provided multiple and large-acreage sites for experimentation and hundreds and hundreds of library samples for aflatoxin analyses. It would not have been possible to complete this work and get registration of the atoxigenic strains of Aspergillus flavus without such immense support by this company and its dedicated personnel. Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

Themis Michailides and Plant Pathologist Mark Doster examine AF36 seeds spread in the field. The atoxigenic AF36 strain was registered for use in pistachio orchards in 2012.

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If you are using irrigation to water, it’s important to know its quality and understand the pounds-per-acre concepts of potentially problematic minerals being applied.

ll throughout the wine grape world and across the U.S., wine grapes are grown on a variety of soil types and climates. AVA regions have started to be defined in places like Arizona where vineyards are thriving

on challenging aridisol soils that can be difficult for Vinifera to thrive in comparison to other longer-established regions. Understanding the parts of the soil report and irrigation water quality have become paramount in under-

standing how to attain the highest level of viable production and maintain the healthiest soils. It’s not uncommon for the focus of soil reports to center on one item in that

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report or look at results in a way that can detract from how to get to a fertility program that will serve the budget, crop and soil health most efficiently. There are five items to look at in order on a soil report to obtain balance and increased overall soil health. It is important when obtaining soil reports to ask the lab you are working with to compute the Cation Exchange Capacity (CEC) and Base Saturation levels. I see a great deal of results from growers who come to my firm looking for recommendations that do not have CEC or base saturation levels defined. It’s impossible to make precise recommendations without these.

developed that it is okay to accept lower P levels and production will not be hindered. In other regions, P levels are normally very adequate. These lower levels of 10 to 25 parts per million (ppm) are widely accepted. It has been observed that controlled vigor and balance are attained when soil P levels are found in the 50- to 100-ppm range. Further observations show that as that number approached 100 ppm, there is improved plant health, controlled vigor and improved

Continued on Page 14

Irrigation Water Quality

Dryland-farmed vineyards don’t have this concern or need worry about the problems associated with irrigation water quality. However, if you are using irrigation to water, it’s important to know its quality and understand the pounds-per-acre concepts of potentially problematic minerals being applied. Normally, water is seen as clear and refreshing; not knowing what is contained in water and what normal usage brings is no different than shoveling on bicarbonates, salts, sulfates, boron and chloride directly on the crop. This is an important place where we can find the sources of issues constraining production and limiting soil health and balance.

Cation Balance

Cation balance is the most important component of a soil report. Many worry most about pH, but the pH will balance itself out when the specific issues are addressed in the soil. Depending on CEC, one should see Ca levels at 60% to 70%, Mg at 10% to 20%, K at 2% to 5%, Na at 1% to 4% and H at 5% to 10%. It’s important to fall back and understand Mulders Chart, realizing the antagonistic and synergistic relationship between minerals in soils. Identifying imbalances in mineral nutrition can lead to soling mysteries behind cropping outcomes. Cation balance is not overly difficult in most cases, granted it may be a situation where there is a two-to-four-year strategy to attain the corrections needed.

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Continued from Page 13 juice numbers. Delivering P can be challenging, but there are good conventional and organic ways to apply. It most likely serves best to look toward a dry program and have a threeto-five-year goal of building soil P to a level that is acceptable.

Organic Matter

Progressive Crop Consultant Ads With don’t No Banners 08132021 RRR.pdfmatter 1 8/13/2021 In the desert southwest, I often see organic

‘

…NOT KNOWING WHAT IS CONTAINED IN WATER AND WHAT NORMAL USAGE BRINGS IS NO DIFFERENT THAN SHOVELING ON BICARBONATES, SALTS, SULFATES, BORON AND CHLORIDE DIRECTLY ON THE CROP.

Cover cropping and getting that green biomass back into the soil is one way to help build a help build soil organic matter levels.

(OM) levels above 1%. Ideally, 4% to 10% is acceptable. In certain regions, this may be a difficult level to attain. Further, in some regions, there can be an issue finding a compost source to help build soil OM levels. Leaning on dry leonardite sources and/or liquid humic additions can be ways to help build soil OM levels. Further, cover cropping and getting that green biomass back into the soil is another means to help build a healthy soil. Increasing OM levels increases CEC, buffers pH and helps nutrient uptake in the soil profile.

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Grapes are not incredibly tolerant of salts and subsequently can be severely hindered by excess amounts. Keeping sulfur, boron and chloride levels to a minimum is very important. Looking at CEC and Ca base saturation levels, one can find the levels acceptable. Keeping boron 1/1000 of Ca or not exceeding 4 ppm is critical to avoid toxicity, with sulfur being 1/3 to 1/2. P is an acceptable range. Cl should be one to two times Na by weight. Soil health does in fact hinge on mineral balance in the soil. Balancing rations between soil minerals is key to allowing for optimal soil health in vineyards. These are simple ways to break down a soil report and what is maybe influencing it. It is important to spend the time, money and all-around effort to address mineral balance and the items discussed here prior to seeking certain products targeted for soil health.

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Mating Disruption of California Red Scale in Citrus By EMILY J. SYMMES | Ph.D., Senior Manager of Technical Field Services, Suterra

alifornia red scale, Aonidiella aurantia, is one of the primary insect pests of citrus crops in California and other states where commercial citrus is grown. Originally native to southeast Asia, it is believed to have arrived in California between 1868 and 1875 and is now distributed worldwide. California red scale (CRS) is a cosmetic pest of fruit that can result in costly economic damage due to downgrades at the packinghouse. In addition, infestations of leaves, twigs and branches can cause overall negative impacts to plant health. As a result, reliance on insecticides has been historically necessary to mitigate damage caused by this pest.

remaining available insecticide chemistries.

During the last half of the 20th century, CRS control relied on the use of broad-spectrum insecticides in the carbamate and organophosphate classes. By the late 1990s, these chemistries were no longer effective in many orchards due to the development of insecticide resistance. In the early 2000s, additional chemistries came to the market and proved valuable to aid in managing CRS. These newer-generation insecticides, based on insect growth regulators, proved effective for several years. Unfortunately, there were still a limited number of insecticide modes of action available for control, and by 2006, resistance to one of the primary insect growth regulators (pyriproxyfen) was confirmed in CRS populations in the Central Valley of California. An integrated pest management approach is necessary to maintain effective control of CRS and extend the lifespan of the 16

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The foundation of integrated pest management (IPM) programs for CRS includes biological control, cultural practices and judicious use of selective insecticides as needed based on monitoring and treatment thresholds. There are effective biological control agents for CRS, including multiple parasitic wasps and general predators. Unfortunately, necessary insecticide applications for the invasive Asian citrus psyllid have reduced the impacts of these natural enemies. More recently, mating disruption has emerged as a fundamental component of successful IPM programs and does not adversely affect natural enemies. Incorporating each of these IPM approaches will benefit growers by reducing crop damage and mitigating further insecticide resistance development.

California Red Scale Biology

Heavy infestation of California red scale. Infestations of leaves, twigs and branches can cause overall negative impacts to plant health (photo courtesy Suterra.)

California red scale male and female mating. Males are extremely shortlived as adults, living approximately six hours, and their only purpose is to locate females for reproduction (photo courtesy UC Statewide IPM Program.)

California red scale typically has four to six generations each year in California depending on growing region and environmental factors. Adult females are sessile and attached to the plant surface, and each produces on average 100 to 150 crawlers. The crawlers are mobile, however longer distance dispersal of crawlers is often due to wind, birds, equipment, or orchard workers. Adult males are the only life stage with wings and capable of flight. Males are extremely short-lived as adults, living approximately six hours, and their only

May / June 2022

purpose is to locate females for reproduction. Mate location is facilitated by a sex pheromone emitted by adult female scales.

Mating Disruption for CRS

Mating disruption for CRS is a technology that utilizes the insect’s sex pheromone as a management tactic to interfere with the ability of males to locate females for reproduction, thereby reducing pest populations and crop damage. This technology has been commercially available in California since 2016, and adoption is increasing each year as positive benefits are observed.

Adult female California red scale. Adult females are sessile and attached to the plant surface (photo courtesy UC Statewide IPM Program.)

A recent publication by leading University citrus researchers summarized a multi-year study demonstrating the efficacy and value of CRS mating disruption in California’s Central Valley citrus production. These studies used the commercially available CRS mating disruption product CheckMate CRS dispensers at the label rate of 180 dispensers/acre. The research team, led by University of California citrus specialist Elizabeth Grafton-Cardwell, concluded several key findings as a result of their 2016-19 studies in 12 commercial citrus orchards. Significant reductions in pheromone trap capture, twig and leaf infestations and infested fruit were consistently demonstrated where CRS mating disruption was applied compared to non-mating disruption reference plots. Suppression of male capture in pheromone traps, an indicator of effective mating disruption, averaged 90%. Twig and leaf infestations were reduced by an average of 75%, and the percentage of highly infested fruit at harvest was less than 0.5% in 9 of the 10 mating disruption blocks in 2018 and 2019. Summary conclusions within the publication state, “mating disruption using CheckMate CRS can be an effective method to reduce California red scale populations throughout the four-plus generations that occur in central California,” adding that “mating disruption has the potential to reduce or eliminate pesticide applications.” It is important to note that the decision to reduce or eliminate any inputs in the overall IPM program should be determined on an

California red scale crawlers. Crawlers are mobile, however longer distance dispersal of crawlers is often due to wind, birds, equipment, or orchard workers (photo courtesy UC Statewide IPM Program.)

Adult male California red scale. The dark band is a key feature for identification (photo courtesy UC Statewide IPM Program.)

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Continued from Page 17 individual basis based on grower and crop adviser consultation.

Implementing CRS Mating Disruption

In general, there are three primary types of mating disruption products or delivery methods. These include vapor dispensers (also called passive dispensers), aerosols and sprayable microencapsulated formulations. The type of delivery method or product that is most effective for a given pest will be based on the pest’s biology and flight behavior as well as the architecture of the cropping systems (i.e., orchard, vineyard or field canopy structure). For example, aerosol-style mating disruption products have been used for many Lepidopteran pests, including codling moth and navel orangeworm in orchard crops for several years. Vineyard crop systems are effectively battling vine mealybug with sprayable formulations or vapor dispensers. Vapor dispensers have also been particularly effective in citrus crop systems to reduce California red scale. The distribution of very small pests, like CRS, is often aggregated in the environment with distinct hotspots. Males are not strong fliers and tend to stay within the tree canopy when searching for mates. This is different from moths, which are stronger fliers

California red scale mating disruption vapor dispensers are designed to consistently permeate the orchard environment with the insect’s sex pheromone precisely within the tree canopy where the pests are located (photo courtesy Suterra.)

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and spend more time flying within the orchard rows in search of mates. Because of this, the current high-density vapor dispenser is the most effective pheromone delivery method for disrupting mating of CRS. Aerosols in their current configurations, which are highly effective for moths, are not as effective for pests like California red scale and vine mealybug (VMB) because of these biological and behavioral differences. Sprayable microencapsulated formulations can be thought of as billions of microscopic dispensers and are therefore also effective mating disruption delivery systems for pests like CRS and VMB. California red scale mating disruption with CheckMate CRS is designed to consistently permeate the orchard environment with the insect’s sex pheromone precisely within the tree canopy where the pests are located. They are applied at a rate of 180 per acre by hand from the ground. Because of pest biology and where populations are most abundant, dispensers should be placed within the tree canopy and not on outer branches. Deployment patterns are based on row and tree spacing and total number of trees per acre. Common row and tree spacing patterns are available on the manufacturer website (Suterra.com) and the manufacturer field team is available to assist with designing dispenser patterns for orchards with other spacings. When possible, dispensers should be placed after pruning, or if before, care taken not to prune out the current season’s mating disruption dispensers. The controlled release of pheromone lasts a full calendar year. Therefore, precise deployment timing is not critical. Many users choose to re-apply their CRS mating disruption dispensers before the historical first or second flights each year.

Benefits of Mating Disruption in the Overall IPM Program

In addition to the validated efficacy in reducing CRS populations and damage, incorporating mating disruption into the overall IPM program for any pest provides additional benefits. PheroMay / June 2022

California red scale mating disruption deployed in the tree canopy. They are applied at a rate of 180/acre by hand from the ground (photo courtesy Suterra.)

mone mating disruption is non-toxic; it does not kill anything. Its efficacy is based on interfering with reproduction, thereby preventing significant portions of subsequent generations from ever existing. This allows all other inputs (cultural, biological, chemical) to have greater impact, simply because there are fewer individuals to have to kill or remove from the environment. This technology is safe for non-target species (natural enemies, pollinators, humans) and is MRL exempt. Mating disruption is not subject to resistance development and may help delay insecticide resistance due to reductions in the number of insecticide applications needed for effective CRS control. Dispenser-based mating disruption for CRS has zero re-entry interval, zero pre-harvest interval and is approved for use in organic agricultural production. References Grafton-Cardwell, E. E., J. T. Leonard, M. P Daugherty, and D. H. Headrick. 2021. Mating Disruption of the California Red Scale, Aonidiella aurantii (Hemiptera: Diaspididae) in Central California Citrus. Journal of Economic Entomology 114(6): 2421-2429. Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

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Biosolarization: Returning Almond Hulls and Shells to the Orchard to Improve Soil and Almond Tree Health By CHRISTOPHER SIMMONS | UC Davis EMILY SHEA | UC Davis TATE LONE | UC Davis AMANDA HODSON | UC Davis RORY CROWLEY | Nicolaus Nut Company and JAMES J. STAPLETON | Kearney Agricultural Research and Extension Center The research found that both biosolarization and solarization are effective methods for the inactivation of lesion and ring nematodes in the short term, but biosolarization may have longer-term suppression (photo courtesy C. Simmons.)

he California Central Valley supplies 80% of almonds globally, so ensuring the health of these trees is essential. However, young trees are highly susceptible to damage from phytoparasitic nematodes, and chemical fumigation is often necessary to ensure protection. Rory Crowley, a conventional almond and walnut grower, partnered with the Simmons lab at UC Davis to find a natural, sustainable yet effective alternative to chemical fumigation.

“Any thoughtful producer in the Central Valley, whether organic or conventional, understands that we simply cannot continue farming the way we are, especially as it relates to traditional chemical fumigation,” Crowley said. “Indeed, as Dr. Amélie Gaudin has recently said, ‘An entire consortium of scientists has argued for years that our current ways of farming simply cannot go on.’ So, we decided to go with something new.”

Implementation and Principle

With current technology, three components are necessary for biosolarization:

Figure 1. Biosolarization schematic.

Researchers in the Simmons lab, working in collaboration with the UC Davis Western Center for Agricultural Safety, specialize in biosolarization, a soil amendment technology that combines biological, thermal and natural chemical control to reduce plant diseases without fumigation. Biosolarization also provides a closed-loop recycling strategy for agricultural waste streams like almond hulls and shells. These byproducts provide valuable soil amendments due to their high organic carbon content and are co-located with almond orchards. Figure 2. Map of field site.

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Soil Amendments: The addition of organic matter (OM) increases the population and activity of beneficial saprophytes (detritus-eaters), which can suppress pathogenic

and a hull and shell mixed waste stream from a local nut processer were selected as soil amendments. Residues were applied to plots at a rate of 15 tons Figure 3. Abundance of the phytoparasitic nematode Pratylenchus vulnus. per acre and tilled to a depth of seven inches. Soil was then organisms through competition or covered with transparent tarp and irrithrough the production of biopesticidal gated to field capacity. For comparison, chemical compounds. Agricultural and additional plots were treated with solarfood processing residues act as low-cost ization (tarped without amendment) or soil amendments for biosolarization. left untreated. Soil remained tarped for six weeks. Transparent plastic tarp: Covering moist soil with a clear tarp promotes soil Nematode Control heating through the greenhouse effect. During hot summer months, covered Parasitic nematodes (lesion and ring) soil can reach surface temperatures over were detected in soils before biosolariza120 degrees F, temperatures which are tion took place. After 10 days of tarping, lethal to many soilborne pathogens and nematodes in the first 12 inches of soil weed seeds. Elevated temperatures can were below detection levels in biosolaralso leave pathogens more susceptible to ized soils and nearly undetectable in biopesticides. solarized soils. Drip line Irrigation: Irrigation using temporary surface drip lines beneath the plastic tarps fills soil pores, reduces oxygen and hinders gas exchange. When the carbon-rich soil environment becomes anaerobic, fermentative bacteria (Bacilli and Clostridia) can rapidly convert carbohydrates from amendments into toxic organic acids and volatiles. These three components act synergistically and can provide positive feedback loops. For instance, high microbial activity stimulated by amendments can consume the limited soil oxygen and produce heat as a byproduct. Similarly, the application of amendments and irrigation can change thermal properties of soil and increase solar heating. Because of these combined factors, effective biosolarization treatment durations can be as short as 10 days or less.

Pre-Plant Orchard Demonstration

Rory’s 8.5-acre almond block in Chico was used as the demonstration site for pre-plant orchard biosolarization in June 2017, and trees were planted the following January. A hull-rich waste stream

When tarps were removed after six weeks of treatment, rows underwent deep tillage in preparation for planting. This effectively reduced nematode levels in the upper 12 inches of soil across all plots regardless of treatment. However, two months after the tillage, reemergence was observed (albeit at low levels) for all but the hull-rich biosolarized plots. As a result, the timing of deep tillage should be considered as a possible complementary control measure. To avoid bringing viable phytoparasitic nematodes from deeper soil layers into the treated root zone, deep tillage should ideally be performed ahead of solarization or biosolarization.

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Soil Ecology Even before tarp application, the incorporation of almond hulls and shells enriched soils with saprophytic taxa (e.g., Bacilli and Streptomyces), demonstrating how amendments can ‘shift’ soil communities to promote organic matter degradation.

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Continued from Page 21 After six weeks of tarping, microbes associated with low-oxygen and highheat environments became significantly enriched in biosolarized and solarized soils (e.g., Clostridia). These microbes can ferment the sugars in almond hulls to produce acetic acid and other biopesticidal chemical compounds.

Figure 4. Relative abundance of key fermentative anaerobe classes (Bacilli and Clostridia) associated with biopesticidal chemical production.

These enriched taxa remained elevated in treated soils even two months post-treatment. This may indicate prolonged degradation of fibrous organic residues, which has been linked to long-term pathogen suppression due to continued biopesticide production. Some of the microbes identified in biosolarized soils have also been associated with improved soil and plant health outcomes.

Orchard Monitoring

Almond tree saplings (Bennett-Hickman, Monterey and Nonpareil varieties with K86 rootstocks) were planted in orchard rows six months post-biosolarization treatment (Jan. 2018), and bi-annual sampling timepoints were used to track soil and crop health through spring 2022. Tree trunk diameters were measured periodically to track growth rate, and soil was periodically sampled to track parasitic nematode re-infestation and soil nutrients levels (Calicum(C), Nitrogen(N), Potassium(K) ). Almond Tree Growth

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Key taxa

Properties in soil

Response to (Bio)solarization

Streptomyces

Saprophytic Production of biocidal volatile compounds, antibiotics, soil vitamins

Enriched in soil after residue incorporation. Enriched 2 months post-treatment.

Bacilli

Saprophytic Fermentation/organic acid formation. Facultative anaerobes: can survive in high and low oxygen environments.

Enriched in soil after residue incorporation. Most abundant taxa detected throughout field trial. Enriched 2 months post-treatment.

Saprophytic Fermentation/organic acid formation. Strict anaerobes: can only survive in low oxygen environments.

Low levels in initial soil samples. High levels detected after 6 weeks of (bio)solarization. Enriched 2 months post-treatment.

Tolerant of high temperatures

Enriched 2 months post-treatment.

Nitrogen fixation and denitrification. Associated with long-term pathogen suppression.

Enriched 2 months post-treatment.

Clostridia

During the first year, trees planted in previously-biosolarized rows seemed to grow slower than trees planted in untreated soils. This trend continued until the beginning of the third year, when growth rate appeared to uniquely accelerate in some treated rows. During the fourth year, no differences in growth rate were found between the control and biosolarized trees, indicating successful adaptation of the trees to the treated soil. In one instance, Nonpareil tree diameters were significantly higher in the shell-rich amended rows. “To be sure, this was a complex project, but the purpose was to prove concept,” Crowley said. “We did that and more. 1After looking at the data, any balanced

Figure 5. Timeline of orchard monitoring.

Burkholderiales Plant growth promotion, fungal suppression, nutrient cycling. Bacteroidota

Table 1. Bacterial taxa enriched in biosolarized or solarized soils.

grower would say that those first two years gave us all a bit of pause. Trunk diameter on the treated row trees were smaller than the controls, yet not once did I think we were going in the wrong direction. I continued to trust Chris and his team, and I trusted the science. I continued to trust my eyes and nose when I smelled the treated soil over against the control dirt. Trunk diameters have now caught up, and in my opinion, will outpace the controls.”

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The slowed growth rate of biosolarized trees during the first and second year followed by accelerated growth during the third year suggests that trees may take at least two years to adjust to disturbances caused by degrading residues, but this did not appear to impact longterm growth rates compared to control trees. This also shows the importance of a post-treatment remediation period before crops are planted, though lab

Continued on Page 24

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Continued from Page 22 studies found soils may recover faster when amendment particle sizes are reduced or applied at lower levels (about 4.5 tons per acre). Nematode Reinfestation

vegetation. Preliminary data have been promising. Certain biosolarized treatments had higher ‘green’ metrics (improved canopy reflectance and color properties) than control trees, indicating greater vegetation levels. However, this benefit was dependent on both soil amendment type and almond tree variety.

he said. “I looked at the control next to it and realized those nuts were ready, dry and shaking off the tree well. When I looked at the biosolarization rows, the nuts were bigger and the quality, by all appearances, was that much better. The nuts were still maturing on the tree, and the overall health of the tree was markedly better. We will prove this out this harvest when we measure crop yield and quality against the controls.”

Conclusions and Recommendations

Both biosolarization and solarization are Three years after initial treatment, nemeffective methods for the inactivation of atode levels remained low in solarized Yield and Ripening lesion and ring nematodes in the short and biosolarized treated rows, but lesion term, but biosolarization may have lonnematode re-infestation was observed in Although we do not have yield and ripger-term suppression. Effects at deep soil the untreated rows. Root knot nemaening data, we do have promising aneclevels (greater than 12”) have not been todes also became more prevalent in dotal evidence from Rory, who managed fullyto investigated. Response (Bio)solarization Keythetaxa Properties in soil control soils after three years. Since the orchard last fall during our second fumigation has been show to control harvest. “I got a call from my shaker Soils treated with biosolarization have Saprophytic major phytoparasitic nematodes for apoperator at Nonpareil harvest: ‘Rory, higher nitrogen, carbon, potassium and Streptomyces Production of biocidal volatile antibiotics, vitamins proximately two years, solarization and compounds, we’ve got a wholesoil row of green nuts.’ I organic matter levels than nonamended biosolarization appear to at least match sped over there in my truck. Lo and soils during the first two years of growth. the efficacy of conventional behold, it was a biosolarization row(s),” With fertilizer prices rising steeply, Saprophytic pesticides. Bacilli fermentation/organic acid formation. Soil Nutrients Facultative anaerobes: can survive in high and low oxygen environments. Over the first three years of growth, Saprophytic biosolarized soils experienced elevated Clostridia Fermentation/organic acid formation. levels of K, N and C as well as organic anaerobes: can only survive in low oxygen environments. matter (OM), aStrict metric associated with improved water-holding capacity, nutrient retentionTolerant and root biomass. After of high temperatures Burkholderiales 3.5 years of treeplant growth, N,promotion, C and OM growth fungal suppression, nutrient cycling. raw values became elevated in control rows, possibly due to increased nutrient Nitrogen fixation and denitrification. Bacteroidota turnover and tree uptake in biosolarized Associated with long-term pathogen suppression. soils. Canopy Health To compare tree health between treatments and tree varieties, multispectral imaging was performed two years after planting and took place each year when the canopy was at peak vegetation. Multispectral imaging captures reflected wavelengths from the orchard to gather data relevant to crop health. For example, healthy vegetation with high chlorophyll levels reflects higher levels of green and near-infrared light than other wavelengths, so rows with more vegetation (and more chlorophyll) would have higher values for green-related metrics than rows with little or poorer 24

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Figure 6. Colorized NDVI. 2 years

3.5 years

Soil Nutrient

3 months

6 months

1.5 years

Potassium

BH and BS > C

BH, BS, S > C

Nitrogen

BH > C

BH and BS > C

C > BS and S

Carbon

BH and BS > C

BS > C

BH and BS > C

C>S

BS > C

BH and BS > C

C>S

Organic Matter

Table 2. Time points are relative to tree planting in January 2018. Listed treatments are significantly elevated: BH – biosolarized with hull-rich residues; BS – biosolarized with shell-rich residues; S – solarized, tarped w/o amendment; C – control, no tarp or amendment.

May / June 2022

enrichment of plant nutrients in biosolarized soils may be an increasingly important driver for adoption for biosolarization over fumigation or solarization.

Trees may take two years to adjust to disturbances caused by biosolarization. Growers should conduct trials on test plots before scaling up. “This powerful alternative to chemical fumigation needs wide adoption, and Chris and his team deserve a huge kudos,” Crowley said. “Onward and upward to the wide adoption and full commercialization of biosolarization with almond hull and shell, and not just in almonds, but in all crops up and down the Central Valley.” Research to translate biosolarization to almond production has been supported by grants from the National Institute of Occupational Safety and Health (grant #5U54OH007550) and the Almond Board of California (grants #17-SIMMONSC-COC-02 and Q18-BIO-18SimmonsC--0). The authors deeply appreciate the collaboration and support of George Nicolaus to establish the field trial on a Nicolaus Nut Company farm. References Hodson, A. K., Milkereit, J., John, G. C., Doll, D. A., & Duncan, R. A. (2019). The effect of fumigation on nematode communities in California almond orchards, Nematology, 21(9), 899-912. Shea, E., Wang, Z., Allison, B., Simmons, C.W., 2021. Alleviating phytotoxicity of soils biosolarized with almond processing residues. Environmental Technology & Innovation. 23, 101662. Shea, E, Fernandez-Bayo, J.D., Hondson, A., et al, 2022. The Effects of Preplant Orchard Biosolarization with Almond Residue Amendments on Soil Nematode and Microbial Communities. Applied Soil Ecology. 172, 104343. Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

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Grapevine Water and Nutrient Management Tips During Drought By GEORGE ZHUANG | UCCE Viticulture Farm Advisor, Fresno County and MATTHEW FIDELIBUS | Extension Viticulturist, UC Davis

Drought-induced Boron deficiency on a Thompson Seedless shoot (all photos courtesy University of California.)

he San Joaquin Valley (SJV) is in the midst of an ongoing drought. Total precipitation in Fresno from October to March was 7.3 inches which amounts to 60% of the historical average of 12 inches. With little or no rain in the forecast and in anticipation of another dry and hot summer, growers might reflect on some environment-related issues observed in 2021.

Maintaining Adequate Soil Moisture is Critical

Many growers who suffered greatly from delayed spring growth (DSG) in 2021 allowed the soil to become too dry the preceding fall or winter. Sufficient carbohydrate con-

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Figure 1. Precipitation, irrigation hours and soil moisture content (volumetric) at a soil depth of two feet from May 2021 to March 2022.

tent of the vines and adequate soil moisture are the keys to dodge DSG. Healthy carbohydrate content in the vines can be attained with a balanced canopy vs yield and a pest-free canopy kept in good condition postharvest. Adequate soil moisture can be achieved through postharvest irrigation or even winter irrigation if precipitation is lacking. Postharvest irrigation helps prevent early defoliation, reduces the chance of winter freeze damage, helps leach any accumulated salts and helps rehydrate the vines after they emerge from dormancy. Thus, a key lesson learned from 2021 should be the importance of maintaining soil moisture during the winter months. The beginning of last winter saw record precipitation, and many growers took proactive measures to prevent DSG in the dry second half of winter in early 2022. For example, in Figure 1, postharvest irrigation (end of September), winter irrigation (mid-November) and early spring irrigation (mid-February) have been noticed from this vineyard, which is one of the collaborative sites contributing to the UC IPM weather station networks (ipm.ucanr.edu/weather/

Continued on Page 28

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Continued from Page 26 grape-powdery-mildew-risk-assessment-index). As a pilot study site, we added a pressure switch and soil moisture probes at soil depth of 1, 2 and 3 feet to help growers improve their irrigation scheduling. We are glad to see growers are taking advantage of those data to manage vineyard water to reduce the risk of DSG. Ideally, a regional soil moisture content network could provide critical winter soil moisture information to guide growers near the station to decide whether to irrigate the vines during the winter month.

Cultural Practices Can Help Protect Against Heatwaves

Besides the severe winter drought, growers also experienced record summer heat in 2021. Max monthly temperature in 2021 was much higher than last 20 years’ average, especially in June and July (Figure 2), and monthly reference evapotranspiration (ETo) in 2021 was also higher than the last 20 years’ average (Figure 3). Sun-exposed clusters and berries under the extreme summer heat will develop sunburn, which will reduce fruit yield and quality, including Brix and raisin B&B grade. I have written a previous article about grapevine heat stress and sunburn management (Progressive Crop Consultant May/June 2019), and many tools

are available for growers: ▶ When developing a new vineyard, row orientation and trellis design can help minimize direct sun exposure to fruit. ▶ Canopy management practices, such as shoot tucking, can help minimize the direct sun exposure to fruits. ▶ Sunblock sprays, such as Kaolin and CaCO3, increase reflectance and thereby reduce solar heating of fruit and leaves. ▶ Evaporative cooling, such as in-canopy micromisting, can be effective, but water use and disease pressure could be increased. ▶ Last but not least, adequate irrigation to develop the canopy which can help shade the fruit and protect fruits.

Figure 2. Monthly max ambient temperature between 2021 and last 20 years’ average. Data are collected from CIMIS Station #80 at Fresno State.

Among all the above options, irrigation might be the most important to prevent fruit sunburn during heat waves, since the sufficient canopy promoted by irrigation does not only serve as the photosynthetic machinery to produce carbohydrate to ripen fruits, but also provides the shade for fruits to reduce excessive sun exposure. There are many irrigation tools which growers can use to watch out for potential water deficit in their vineyards: ▶ Soil moisture-based irrigation. ▶ Plant water-based irrigation. ▶ Weather-based irrigation. Most growers I have talked to have soil moisture sensors on-site, and currently, CDFA offers various grants (cdfa. ca.gov/oefi/sweep/) to help growers install soil moisture sensors.

Figure 3. Monthly ETo between 2021 and last 20 years’ average. Data are collected from CIMIS Station #80 at Fresno State.

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No matter which soil moisture sensor you have, the key is to identify the soil moisture benchmark which you can target the irrigation to. So, how can soil moisture sensors help you to target

Continued on Page 30

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Figure 4. The relationship between midday leaf water potential measured on Thompson Seedless grapevines and soil water content (SWC, measured as the percent of volume). At the study site of UC Kearney REC, the soil type is Hanford fine sandy loam and 10% to 15% SWC correlates to -1.2 to -0.9 MPa midday leaf water potential, which is regarded as mild water stress or no water stress for the SJV grapevines.

Continued from Page 28 the benchmark and manage the water in your vineyard? For example, based on Figure 1 (see page 26), from May 2021 to August 2021, growers utilized the soil moisture sensor (soil water volumetric sensor, Campbell Scientific CS655) to schedule the irrigation to

maintain the soil moisture content range from 10% to 15% at soil depth of two feet. On this site, three soil water volumetric sensors were installed at approximately one foot from the vine trunk and six inches from the emitter. Sensors were set at the depth of one, two and

three feet beneath the soil surface. We assume growers are satisfied with the canopy and crop development during the season, and a field study done by Dr. Larry Williams at UC Kearney REC also shows 10% to 15% soil moisture content correlates to -1.2 to -0.9 MPa midday leaf water potential (Williams 2012). The range from -1.2 to -0.9 MPa of midday leaf water potential is regarded as mild water stress or no water stress for the SJV vines and can be used to maximize the crop production (Figure 4). Given the soil type on this site is similar to the Hanford fine sandy loam soil in UC Kearney REC, the same range of soil moisture content can serve as a good benchmark for any future irrigation scheduling on this site. Please note that no water applied after mid-August aimed to prepare the soil for raisin drying. Unsurprisingly, in 2022, growers started the early spring irrigation in mid-February to target the same range of soil moisture content from 10% to 15% to prepare the budbreak and early shoot development. Therefore, growers can irrigate the grapevines by selecting the desired soil moisture benchmark based on the preferred canopy and crop development on your specific soil type.

Nutrient Management During Drought

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Low rainfall in autumn to midwinter can cause drought-induced boron deficiency. The symptoms are erratic budbreak, stunted and distorted shoots, misshapen and chlorotic leaves. The most classic symptoms after budbreak are dwarfed shoots that grow in a zigzag manner with numerous lateral shoots, and the tip of the primary shoot may die. Most shoots begin to elongate normally by late spring, but cluster size may be reduced. The cause is believed to be a late-season drought-induced boron deficiency that affects development of shoots within dormant buds. The key to reduce drought-induced boron deficiency is postharvest irrigation. Traditionally, Thompson raisin vineyards go through the harvest and raisin-drying processes for a nearly two-month period without irrigation

(Figure 1, see page 26). The postharvest irrigation can relieve the water stress and maintain a healthy functional canopy to avoid boron deficiency. Spring fever is sometimes referred to as false potassium deficiency because the leaf symptoms resemble and are sometimes confused with potassium deficiency. Alternating warm and cold weather patterns before bloom, as has been observed this spring, can cause a temporary nitrogen metabolism disorder associated with high levels of ammonium and the polyamine putrescine in the leaves. Symptoms occur in basal leaves and leaves in the fruit zone. Lower leaf color fades and becomes chlorotic in spring, beginning at the leaf margins and progressing between the primary and secondary veins. Leaf margins may become slightly necrotic, marginal necrosis is significant and affected leaves can drop.

Spring fever in basal leaves of Thompson Seedless, showing chlorosis, curling and browning of leaf margins.

There is no cure for spring fever, and petiole/blade laboratory analysis can differentiate true K deficiency from spring fever. Spring fever typically will fade as the weather warms up and the onset of symptomatic leaves decreases around bloom; however, blades with existing symptoms will remain. References

Christensen, Pete. Raisin Production Manual. University of California Agriculture and Natural Resources. 2000. Williams, L. (2012), Effects of applied water amounts at various fractions of evapotranspiration (ETc) on leaf gas exchange of Thompson Seedless grapevines. Australian Journal of Grape and Wine Research, 18: 100-108. https://doi. org/10.1111/j.1755-0238.2011.00176.x

Bettiga, Larry. Grape Pest Management, Third Edition. University of California Comments about this article? We want Agriculture and Natural Resources. 2013. to hear from you. Feel free to email us at article@jcsmarketinginc.com

(559)584-7695 or visit us as www.superiorsoil.com Serving California since 1983

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Mechanization Improves Pruning Efficiency in Table Grape Vineyards By TIAN TIAN | UCCE Viticulture Farm Advisor, Kern County

Figure 1. Andros pre-pruner in a spur-pruned vineyard. The machine snaps canes and removes part of the wood materials before workers cut canes to spurs (all photos courtesy T. Tian.)

echanization is clearly one of the best solutions to reduce labor requirements for vineyard management and lower production cost. Even though pruning machines are extensively used in wine grapes grown in the San Joaquin Valley, the mechanization of pruning in table grapes remains challenging.

Most of the table grape vineyards grown in the San Joaquin Valley use a “Y” trellis system (open Gable system). This highly structured trellis provides adequate support to large canopies of table grapevines but limits the options of mechanization. In addition, table grapes have high aesthetic requirements. Growers rely on vineyard crews to adjust the location and numbers of spurs and canes at pruning to maintain vine shape and achieve desirable yield and fruit quality. In this regard, mechanical tools that are currently available cannot mechanize the entire pruning process in table grape vineyards. However, mechanizing part of the process is possible. Cane pruning, spur pruning and spur pruning with kicker canes are used in table grape vineyards, and the choice of method is based on basal bud fruitfulness of specific varieties and growers’ preferences. Despite the difference in pruning methods, there are three general steps involved, including 1) selecting canes and cutting canes to desirable length; 2) pulling pruned canes off the catching wires and placing them between rows; and 3) tying canes or new cordons to the wire. Mechanization has the potential to improve efficiency in the latter two steps. 32

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Figure 2. KLIMA cane shredder in a spur-pruned vineyard. The machine strips canes from the wires and mulches them after an initial pass of cutting canes.

Figure 3. Battery powered pruning tools (left, tying machine; right, pruning shear). These tools are alternatives to conventional hand shears, expected to reduce the fatigue of workers and lower the risk of repetitive motion injuries

Andros Wye trellis pre-pruner (Andros pre-pruner) snaps canes and removes part of the wood materials before workers cut canes to spurs (Figure 1). KLIMA cane pruning system (KLIMA shredder) strips canes from the wires and mulches them after an initial pass of cutting canes (Figure 2). Battery-powered shears are alternatives to conventional hand shears, expected to reduce the fatigue of workers and lower the risk of repetitive motion injuries (Figure 3). Battery-powered tying machines simplify the tying process May / June 2022

and may reduce the time needed to tie individual canes. Despite the promising outlook of mechanical pruning tools, more evaluation is needed on their suitability in different training systems and whether mechanization can decrease labor requirements for pruning. Thus, as supported by the California Table Grape Commission, we

Continued on Page 34

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Continued from Page 32 evaluated those four mechanical pruning tools in four different table grape vineyards in 2022 between January and March.

KLIMA Cane Pruning System

We evaluated the KLIMA shredder in a spur-pruned ‘Holiday’ vineyard and a cane-pruned ‘Autumn King’ vineyard. Self-releasing clips were installed on the “V” cross arms in both vineyards prior to the evaluation (Figure 4). Those clips allow the shredder to directly pull catching wires from cross arms without human assistance. In each vineyard, 7 to 10 continuous rows were hand-pruned, and the adjacent 7 to 10 rows were pruned using the adjusted procedure. On the first day, workers cut canes to desirable lengths without pulling pruned canes off the wire. On the second day, the KLIMA shredder was hooked to a tractor for passes in the vineyard. In each pass, the shredder caught the catching wires, releasing them from crossarms, stripped canes from the wires and mulched those canes. A worker was assigned to guide the tractor driver. The time required for shredding ranged between 1.5 and 2 hours per acre. On the third day, workers replaced catching wires back to crossarms. When the KLIMA shredder was used, the non-machine labor hours required to prune vines reduced by 26% to 34% (Table 1), leading to a savings of $150 to $200 per acre on labor costs. A greater reduction in labor requirement was observed in the spur-pruned vineyard than in the cane-pruned vineyard. It seems the KLIMA shredder conveys a greater benefit in vineyards where pulling canes off the wire takes similar or more time than cutting canes. Indeed, we found that workers spent a similar amount of time on cutting and pulling canes in the spur-pruned vineyard. In the cane-pruned vineyard, on the other hand, workers used 65% of the time on cutting canes and 35% of the time on pulling canes.

Andros Pre-Pruner

We assessed the single-head model of Andros pre-pruner in the spur-pruned ‘Holiday’ vineyard that was used for KLIMA

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Figure 4. Self-releasing clip installed on a “V” cross arm. These clips Non-machine labor required Non-machine labor required to allow the shredder tovines directly from to prune vinescross in a 7 xarms 12 prune in a 7 xpull 11 catching wires cane-pruned vineyard without humanspur-pruned assistance.vineyard (hours/acre) (hours/acre)

Using Andros pre-pruner

Conventional pruning Using Andros pre-pruner Using KLIMA cane shredder1

Average Maximum Minimum Average Maximum Minimum Non-machine labor required Non-machine labor required to 27.2 24.6 31.9to prune44.2 48.1 33.9 vines in a 7 x 12 prune vines in a 7 x 11 cane-pruned vineyard spur-pruned vineyard (hours/acre) (hours/acre) 18.7 41.1 30.7 Average Maximum Minimum Average Maximum Minimum 27.2 44.2 24.6 31.9 48.1 33.9 18.4 27.7 15.2 23.7 29.2 22.5

30.7

41.1

18.7

22.5

29.2

15.2

23.7

27.7

18.4

Table 1. Non-machine labor required to prune vines with and without mechanization. Time required for tying canes is not included.

Using conventional hand shears Using batterypowered shears

Non-machine labor required to prune vines in a spur-pruned vineyard (hours/acre)

Non-machine labor required to prune vines in a cane-pruned vineyard (hours/acre)

Average Maximum Minimum

35.5

62.3

24.2

47.5

58.0

35.5

32.1

43.8

25.1

45.1

69.2

36.3

Table 2. Non-machine labor required to prune vines using conventional hand shears versus battery powered shears

shredder evaluation. Ten continuous rows were pre-pruned and then hand pruned. The adjacent 10 rows were hand-pruned. Andros pre-pruner covered one acre in an hour, leading to a 10% decrease in non-machine labor required for pruning (Table 1). The reduction of labor requirements resulted in a savings of $40 to $80 on a per-acre basis. Given the trellis configuration of the experimental vineyard, the cutting system was placed 20 to 25 inches (51 to 63 cm) above the cordon to avoid the cutting system hitting the horizontal bars of crossarms. In vineyards with larger “V” crossarms, the cutting system can be placed closer to the cordon and thus a larger portion of the wood materials can be pre-pruned. In this case, the cost savings reached $120 to $130 per acre. In addition to cost savings, workers suggested benefit on their end; it was easier to pull canes off when they were pre-cut.

Battery-Powered Pruning Tools

We tested battery-powered pruning shears in a spur-pruned ‘Scarlet Royal’ vineyard. Workers who used battery-powered shears can prune two to four more vines per hour as compared to workers using conventional hand shears, leading to a 10% reduction in manual labor input (Table 2, see page 34). Workers using battery-powered shears felt less fatigue and pruned at a similar pace throughout the day, while workers using conventional hand shears clearly slowed down after 11am.

dros Engineering. This project is funded by the California Table Grape Commission. Please contact Tian at titian@ucanr.edu for more information. Resources Andros pre-pruner: andros-eng.com/ ag-equipment/agile-pruning-implements/

KLIMA cane shredder: pellencus.com/ products/vineyard/pruner-klima-cane/ Pellenc battery-powered tools: pellencus. com/products/hand-tools/

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

We also examined battery-powered pruning shears and tying machines in a canepruned ‘Autumn King’ vineyard. The use of tying machine allowed workers to tie five to nine more vines per hour than manual tying, improving tying efficiency by 15%. However, battery-powered shears did not improve pruning efficiency, even though workers felt more comfortable making difficult cuts when using those shears (Table 2, see page 34). Growers and the manufacturer observed a larger decrease in labor requirements when battery-powered tools were used under similar conditions. We suspect workers who participated in the trial did not fully adapt to the new tools, given that they only practiced for a day prior to the evaluation. We plan to perform more evaluations on those tools in 2023. Mechanization of pruning can effectively reduce labor requirement and improve efficiency. Depending on the trellis configuration and production scale, growers could save $40 to $200 per acre by adopting mechanical pruning tools. Besides cost savings, pruning mechanization conveys benefits in other aspects. For example, workers could pull off pruned canes more easily after pre-pruning. KLIMA shredder shreds canes in pieces smaller than regular ground shredders, allowing wood materials to break down faster. The quality of cuts and ties improves when battery-powered tools are used. We truly appreciate the support from table grape growers in Tulare and Kern counties, Pellenc America Inc. and AnMay / June 2022

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Aspergillus Vine Canker: An Overlooked Canker Disease of Grapevine in California By MARCELO BUSTAMANTE | Department of Plant Pathology, UC Davis, KARINA ELFAR | Department of Plant Pathology, UC Davis, MOLLY ARREGUIN | Department of Plant Pathology, UC Davis, GEORGE ZHUANG | UCCE Viticulture Farm Advisor, Fresno County and AKIF ESKALEN | Department of Plant Pathology, UC Davis

Figure 1. Affected vines are easily distinguishable by their premature senescent leaves during the fall, while healthy vines are still green (all photos courtesy A. Eskalen.)

rapevine canker diseases are commonly associated with fungal pathogens of the Botryosphaeriaceae, Diatrypaceae and Diaporthaceae families. These pathogens have been found and described in many cultivars worldwide. Symptoms include internal wood necrosis, stunted or poor shoot development after the budbreak and dieback of cordons or the entire vine. Cankered tissues may also exhibit dark fruiting bodies (pycnidia and perithecia) on the surface, which are responsible for releasing the spores that will lead to further infections in the vineyard.

A different wood canker disease was

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first detected in the San Joaquin Valley in 1989, affecting excessively vigorous young ‘Red Globe’ grapevines (Michailides et al. 2002). Since then, the disease has been observed on different cultivars, including Chardonnay, Grenache and Crimson Seedless. The pathogen was morphologically identified Aspergillus niger, a member of the group of black aspergilli, or Aspergillus section Nigri, and the disease was named as Aspergillus Vine Canker. From 2003 to 2010, Aspergillus vine canker was detected and monitored in Italy, affecting several table grape cultivars on different growing regions (Vitale et al. 2008, Vitale et al. 2012). In this case, three species of black aspergilli were associated (A. awamori, A. carbonarius and A. tubingensis). Recently, through a collaboration with UCCE farm advisors, we identified Aspergillus vine canker on Grenache and Malbec cultivars in Fresno and Sonoma counties, respectively. Symptomatic vines tested negative for viral infections.

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Figure 2. Black sporulation is evident at the surface and underneath the bark of affected tissues, which is key to distinguish Aspergillus from other trunk pathogens that usually form fruiting bodies that are embedded in the wood.

Symptoms

Affected vines are easily distinguishable by their premature senescent leaves during the fall, while healthy vines are still green (Figure 1). A single vine can harbor multiple cankers located on different parts of the vine, including the trunk, cordon and spurs. Black sporulation is evident at the surface and underneath the bark of affected tissues, which is key to distinguish Aspergillus from other trunk

pathogens that usually form fruiting bodies that are embedded in the wood (Figure 2, see page 36). Internally, a brown discoloration is evident in the xylem near the margin of the cankers (Figure 3a), whereas the areas under the sporulation show necrosis and black discoloration near the bark (Figure 3b). In severe cases, the canker can girdle most of the vascular area.

Current Investigations

Our lab has been focusing on the specific identification of the causal agent of Aspergillus vine canker in California using molecular tools, particularly by constructing phylogenetic trees using DNA sequences of the calmodulin gene. Preliminary data suggest that our isolates correspond to Aspergillus tubingensis, a closely related species to the previously identified A. niger. Since morphological features cannot separate

Continued on Page 38

Figure 3a and 3b. Internally, a brown discoloration is evident in the xylem near the margin of the cankers (left), whereas the areas under the sporulation show necrosis and black discoloration near the bark (right).

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Continued from Page 37 both fungal species, two hypotheses can be indicated, either the old and new isolates correspond to the same species (A. tubingensis) or they are different (A. niger and A. tubingensis). Coincidently, black aspergilli are known to cause sour rot on grape berries. In California, two species (A. niger and A. carbonarius) have been described as causal agents of sour rot disease on table grapes (Rooney-Latham et al. 2008). Therefore, we are currently studying the phylogenetic relationships between Aspergillus isolates from wood cankers and sour rot berries to understand accurately the etiology and epidemiology of both diseases.

Management Strategies

Aspergillus vine canker has not been thoroughly studied given its sporadic occurrence in California. Therefore, the only management strategies include cultural practices, such as obtaining clean plant materials, identifying diseased vines in the fall and removing

affected parts by cutting them back below the canker during dormant season or removing the entire vine. References Michailides, TJ., W. Peacock, P. Christensen, DP. Morgan, D. Felts. 2002. Plant Dis. 86:75. https://doi.org/10.1094/ PDIS.2002.86.1.75A Rooney-Latham, S., C. N. Janousek, A. Eskalen, W. D. Gubler. 2008. Plant Dis. 92(4):651. https://doi.org/10.1094/PDIS92-4-0651A Vitale, A., Castello, I., Polizzi, G. 2008. Plant Dis. 92:1471. https://doi. org/10.1094/PDIS-92-10-1471B Vitale, A., G. Cirvilleri, A. Panebianco, F. Epifani, G. Perreno, G. Polizzi. 2012. Eur J Plant Pathol 132:483–487 https:// doi.org/10.1007/s10658-011-9906-z

’

‘The only management strategies include cultural practices, such as obtaining clean plant materials, identifying diseased vines in the fall and removing affected parts by cutting them back below the canker during dormant season or removing the entire vine.’

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