Progressive Crop Consultant - March/April 2021 by JCS Marketing, Inc.

March / April 2021

A Review of Pythium Diseases in Row Crops A New Generation of Precision Spray Technology Using N-Rich Reference Zones in Small Grains Plastic Mulches Reduce SWD in Raspberry

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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

4 8 12 18

A New Generation of Precision Spray Technology

CONTRIBUTING WRITERS & INDUSTRY SUPPORT Amaya Atucha

University of Wisconsin, Madison

Using N-Rich Reference Zones to Inform In-Season Nitrogen Fertilization Practices in California Small Grains A Review of Pythium Diseases in Row Crops

Steve Booher

Konrad Mathesius

Nick Clark

Hanna McIntosh

Warren E. Clark

Themis J. Michailides

Surendra K. Dara

David Morgan

Contributing Writer

UCCE Entomology and Biologicals Advisor

Giuliano Galdi

Plastic Mulches Reduce Spotted-Wing Drosophila Infestation in Fall-Bearing Raspberry

30 36

Enhancing Diamondback Moth Management with Mating Disruption

Life After Methyl Bromide in California Berries

Understanding CCA Certification Exams

UC Cooperative Extension UC Cooperative Extension

Taylor Nelsen

Tom Getts

Jerome Pier Ph.D.

Christelle Guédot

University of Wisconsin, Madison

Steven Koike

Michelle Leinfelder-Miles UC Cooperative Extension

CCA, PCA, Board Chairman, Western Region Certified Crop Advisors

Zheng Wang

UCCE Vegetable Crops Farm Advisor, Stanislaus County

Heping Zhu

Agricultural Engineer and Lead Scientist, USDA-ARS Application Technology Research Unit

Sarah Light

UC Cooperative Extension

Vegetable Growers Express Impressions, Concerns and Hope for Crop Biostimulants

University of Wisconsin, Madison

Department of Plant Sciences, UC Davis

TriCal Diagnostics

UC Cooperative Extension

UC Cooperative Extension UC Cooperative Extension

New Findings on Limb Dieback of Figs in California

Department of Plant Sciences, UC Davis

Founder & CEO, Smart Guided® Systems, LLC UC Cooperative Extension

Mark Lundy

UC COOPERATIVE EXTENSION ADVISORY BOARD Surendra Dara UCCE Entomology and Biologicals Advisor, San Luis Obispo and Santa Barbara Counties

Kevin Day

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

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.

March / April 2021

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A New Generation of Precision Spray Technology New retrofit kit creates automated universal intelligent spray control system for existing sprayers that could benefit growers and the environment. By HEPING ZHU | Agricultural Engineer and Lead Scientist, USDA-ARS Application Technology Research Unit and STEVE BOOHER | Founder & CEO, Smart Guided® Systems, LLC

ruit, nut, ornamental nursery, horticultural and greenhouse industries are among the fastest-growing enterprises in US agriculture. Application of pesticides and other production strategies have ensured their high-quality products meet stringent market requirements. However, low-efficiency, decades-old spray technologies are commonly used to treat these specialty crops and have caused an enormous amount of pesticide waste, additional costs in crop production and concerns around worker safety. The pesticide waste has also caused environmental contamination and ecosystem damage because pesticide sprays indiscriminately kill both pests and beneficial insects. Spray drift and off-target loss will likely remain a major problem as long as pesticides are applied using indiscriminate spray equipment.

spray management program for pests and diseases should include improved delivery systems that are flexible for spraying the amount of chemicals to match tree structures instead of acreage base. Such spray application will also produce minimum spray drift and off-target loss of pesticide on the ground and in the air.

To achieve this goal, a new automated universal intelligent spray control system was developed as a retrofit kit to attach on existing sprayers. With the intelligent control system, the conventional spraying systems can determine the presence, size, shape, and foliage density of target plants such as trees and grape vines, and then automatically apply the amount of pesticides as needed according to plant architectures in real time. With the control system, growers themselves can upgrade their own sprayers to precision Need for Efficient Technologies sprayers with intelligent functions Pesticide application is the most rather than buying new sprayers, and complicated operation in crop produc- sprayer manufacturers do not need to tion because there are many variables change their current sprayer designs. affecting spray strategies and practices. The primary requirement for the In many cases, when decisions must upgrade action is to connect a varibe made to apply chemicals within a able-flowrate solenoid valve to each very narrow time window in response nozzle, and all other components are to escalating pest pressure, a simple attached to the sprayer body without “best guess” practice is often under changing the sprayer structure. vague labeling of pesticide rates to control pests that may result in excesThis new system is the product of a sive application of pesticides. decade of research and development by engineers at USDA-ARS at Wooster, Given constrained environments for Ohio in collaboration with researchers specialty crop production, an ideal at The Ohio State University, Oregon

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March / April 2021

State University, University of Tennessee, Clemson University, Texas A&M University, Iowa State University, Washington State University, Penn State University, University of Queensland and USDA-ARS. Since 2013, the system has been tested as a retrofit on different types of the air-blast sprayers for pest control effectiveness, reliability and repeatability on real farm fields. Comparative field biological tests were also conducted to evaluate insect and disease control for the sprayers with and without the intelligent-decision control capabilities in commercial nurseries, apple orchards, peach orchards, pecan orchards, vineyards and small fruit productions as well as university research farms in Ohio, Oregon, Tennessee, South Carolina, Texas, California and Washington. These activities were voluntarily held by UCCE in Napa County and University of Queensland in Australia.

System Features

Spray deposition uniformity insidecanopies, chemical usage and off-target losses were investigated for the plants at different growth stages in ornamental nurseries, apple orchards, peach orchards and vineyards. Multiyear field tests have demonstrated the intelligent spray system is reliable and can reduce pesticide use in a range between 30% and 90%, reduce airborne spray drift between 60% and 90%,

Figure 1. Integration of universal intelligent spray control system as a retrofit kit into existing sprayers.

All components of the smart sprayer retrofit kit are attached to the sprayer body without changing the sprayer structure, with the exception of connecting a variable-flowrate solenoid valve to each nozzle.

and reduce spray loss to the ground between 40% and 80%, resulting in chemical savings in a range of $56 to $812 per acre annually. At the same time, the insect and disease control efficiencies are comparable or even better than standard sprayer practices. Because it uses less spray volume, it can spray more acres with the same amount of tank mixtures, thus reducing tank refilling times and reducing labor and fuel costs. As a result, Smart Guided Systems, LLC commercialized the intelligent spray system, and a commercial version of the product has been developed with joint efforts between USDA-ARS and Smart Guided Systems, LLC. The new control system (See Figure 1) includes a new laser sensor, an Android Samsung tablet, a GPS navigator, an automatic flow rate controller, air filtration unit, a toggle switch box and a universal mounting kit.

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The laser sensor is mounted between the tractor and the sprayer to “see” plants on both sides of the sprayer. It releases 54,000 detection signals per second with a 270-degree and 164ft radial detection range. The laser signals bounced back from the plant

Continued on Page 6

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March / April 2021

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Continued from Page 5 canopies is used to determine the presence of a plant canopy and measure the canopy height, width, foliage density and canopy foliage volume (Figure 2). The GPS navigation device (or the radar speed sensor mounted at the bottom of the sprayer) measures sprayer travel speeds and location of each plant in the field. Based on the plant canopy foliage volume and the sprayer ground speed, the amount of spray for each nozzle is determined and then discharged to different parts of each plant in real time. Each nozzle is connected to a 10 Hz pulse width modulation (PWM) solenoid valve, and the nozzle flow rates are controlled by manipulating the duty cycle of the PWM waveforms with the flow controller. The flow controller consists of microprocessors to generate flow rate commands for each nozzle to discharge variable spray rates. Field data collected and processed with the intelligent spray system are synchronized through the tablet WiFi to the cloud.

Figure 2. Laser sensor signals are used to measure canopy architecture and then manipulate individual nozzle flow rates as the function of the sectional canopy foliage volume and travel speed in real time.

suggested to be higher than 5 MPH for orchard spray applications.

The Android tablet provides the information for operators to communicate with the spray control system. The screen displays the sprayer travel speed, total discharged spray volume, spray width, and active nozzles. The operator can use the touch screen to modify the spray parameters as needed. The tablet allows the operator to activate the sprayer output on one or both sides in manual or automatic mode. All the electronic devices are powered by a 12V DC tractor battery. Another precaution includes the air filtration unit to discharge filtered air to prevent the laser sensor surface from getting dust and droplets. The toggle switches on the switch box are used to turn on/off main power, turn on/off the air filtration unit manually and override the automatic controller to activate nozzles as needed. Because sprayer travel speeds are automatically measured and included in the spray output control, applicators do not need to specify how fast they drive the tractor. However, travel speeds are not

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Features in the commercial system also include tree counting, tree size, foliage density heat map comparison capability, liquid volume sprayed per plant, maps of sprayed plant locations, ability to turn nozzles on/off independently through the tablet screen, cloud sync feature, web portal for configuration settings and spray coverage report view, system log files, five different languages (English, Spanish, French, German and Italian), and options for choosing metric or imperial units. The commercial products have been used by growers in the US and other countries with crops including citrus, nursery, pecan, blueberry, peach, almond, apple and pear with pesticide usage reductions in the range between 30% to 85% depending on crop types and growth stages. John Deere also established an agreement with Smart Guided Systems to sell the commercial intelligent spray control system for use in high-value crop applications through their dealer network. The intelligent spray control system advances conventional standard pesticide application systems with the flexibility to spray specific positions on the plants. It reduces human involvement in

March / April 2021

decisions on how much spray volume is needed because the spray volume applied in the field is automatically controlled by the plant foliage volume instead of the antiquated gallons per acre. The conventional air-blast spray system has been used from generation to generation for almost 80 years because of its robustness. Growers have accumulated extensive experience on using it to control pests in accommodation with their own crops. After being retrofitted with the intelligent spray control system, the conventional sprayers are able to turn on and off each nozzle and will stop spraying non-target areas such as gaps between trees, on the ground and above trees while their capabilities of spray penetration, spray range and spray deposition quality on plants remain the same. This new generation of spray technology is anticipated to be a primary precision spray technology for future decades to save chemicals for growers and provide a sustainable and environmentally responsible approach to protecting crops. Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

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Using N-Rich By MICHELLE LEINFELDER-MILES | UC Cooperative Extension Reference Zones to NICK CLARK | UC Cooperative Extension TAYLOR NELSEN | Department of Plant Sciences, UC Davis Inform In-Season TOM GETTS | UC Cooperative Extension KONRAD MATHESIUS | UC Cooperative Extension Nitrogen Fertilization SARAH LIGHT | UC Cooperative Extension GIULIANO GALDI | UC Cooperative Extension Practices in California and MARK LUNDY | Department of Plant Sciences, UC Davis Small Grains

plant applications. The reference zone is a relatively small area within the field where extra N fertilizer is added at the beginning of the season. This extra fertilizer ensures that the reference zone will not be N-limited from planting until an in-season fertilizer decision is made. When a grower is determining whether and how much N fertilizer to add in-season, measurements from both the reference zone and the broader field are compared to understand whether the broader field is sufficient in plant-available N.

ver the last year, a team from UCCE has been working with California small grains growers on practices that can improve nitrogen (N) use efficiency. At demonstration sites, we have implemented practices that UC Grain Cropping Systems Specialist Mark Lundy has been investigating for several years, namely N-rich reference zones, a soil nitrate quick test, handheld reflectance devices and aerial imagery. We demonstrate how to use these tools to manage N fertilizers in small grain crops across variable soil and climatic conditions in the Sacramento Valley, Delta, San Joaquin Valley and Intermountain Region. The demonstrations are funded by the CDFA Fertilizer Research and Education Program and a USDA-NRCS California Conservation Innovation Grant. Our goal is to help growers and consultants learn and implement these practices to guide N fertilization in small grains, thereby increasing crop productivity and N use efficiency while reducing potential for N loss to the environment.

What are “N-Rich Reference Zones”?

Fertilizer N Rate and Field Variability

Reference zones are most useful to growers who can apply the majority of their seasonal N budget during or after the tillering stage of growth. Previous work has shown that N fertilizer applied during the season−between the tillering and heading stages of small grain development−results in higher yields, higher protein and increased fertilizer use efficiency compared to pre8

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Fertilizer N rate and field variability are two important considerations when creating N-rich reference zones. The amount of N to apply in the N-rich zone will depend on several factors such as yield goal, protein goal and when the expected in-season fertilizer application will take place. There should be sufficient N applied to the reference zone at planting to ensure that the plants in the zone are not limited by N at the stages of growth when the in-season fertilizer is applied. Table 1 (see page 9) gives some examples of how much N fertilizer to apply to the N-rich zone for a range of potential yields. It is important to establish the N-rich zones in representative parts of the field. Areas of the field that are unique (i.e. low areas, high areas, gravel strips, etc.) should be avoided. It is also important that the zones capture field variability. If certain areas have

March / April 2021

distinct soil types or known patterns of yield or management differences, a grower should establish multiple zones to account for these sources of spatial variability if they represent large areas in the field. Soil maps (available from casoilresource.lawr.ucdavis.edu/ soilweb-apps/) and historical aerial imagery can often help in identifying field patterns and good location(s) for reference zones.

How and When to Apply the N-Rich Zone Fertilizer

A grower can establish N-rich zones during the pre-plant fertilizer application. For example, a grower may apply 50 pounds N per acre across the field and then make another pass or two in the zone to apply an additional 50 to 100 pounds N per acre (depending on what the grower calculates is necessary, as described above.) This method might be most easily adopted by growers. We have observed, however, that if the fertilizer is placed too deep in the soil profile, the N may not be readily available to the seedling crop early in the season because it is below the root zone. Therefore, N-rich zones established by this method may not provide a reliable early-season point of comparison. Instead, we have found that broadcasting urea is the most effective way to establish N-rich zones. At our demonstration sites, we broadcasted urea after tillage or shortly after planting, but always ahead of a storm or irrigation event that could incorporate the fertilizer. Orienting the zones perpendicular to the rows or tractor passes also helps

Average Yield (lb/ac, 12% protein)

Crop stage of assessment/application

N rate (lb/ac) needed in N-rich zone

3000

tillering

5000

tillering

110

7000

tillering

150

3000

flag leaf

120

5000

flag leaf

200

7000

flag leaf

275

Table 1. Approximate N fertilizer application rates suggested for use in N-rich reference zones based on a range of average yields and two stages of crop growth. Suggested rates ensure that crops within the reference zone are not N-limited when an in-season fertilizer application decision is being made at the crop stage indicated.

to capture field variability. When the zones are too narrow and run in the same direction as the field work, it can be hard to differentiate between a field pattern associated with equipment passes and a N effect, particularly early in the season.

Monitoring the Field

Once the crop begins to grow, the field should be monitored periodically to

assess whether the crop is likely to respond to a N fertilizer application. A combination of the soil nitrate quick test (SNQT) and plant reflectance measurements taken from both the N-rich zones and the broader field can indicate when a top-dress fertilizer application may be beneficial. The soil nitrate quick test and plant reflectance measurements complement other important information like current crop growth

stage, crop yield and protein goals, and local weather records to inform a site-specific N fertilizer recommendation. The SNQT is a simple and low-cost test that provides a ballpark estimate of the soil nitrate-N concentration in the root zone. Nitrate is a highly plant-available

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Figure 1. The GreenSeeker held above a recently headed small grain and displaying the NDVI value. Values range from 0 to 1 (i.e. less-green to very green plants).

Figure 3. Small grain leaf inserted in the sampling area of the at LEAF showing a chlorophyll reading in the lower right corner of the display while the user’s back shades the device.

Figure 2. A field in Solano County where three N-rich reference zones are visible at tillering using NDRE captured via drone (left), but not visible to the naked eye (right).

Continued from Page 9 form of N. Using the SNQT when N fertilizer decisions are being made will help to narrow a range of fertilizer rates appropriate for that field. More information on using the SNQT in small grains, including a sample protocol and demonstration video, is available at smallgrains.ucanr.edu/Nutrient_Management/snqt/. Over the past several years, UCCE agronomists have developed a strong relationship between the value measured using the SNQT and an estimate of fertilizer N equivalence. Crop reflectance can be measured using a number of tools, including handheld devices, drones and satellite imagery. Common indices that result from measurements of canopy reflectance are normalized difference vegetation index (NDVI) and normalized difference red edge index (NDRE). These indices represent measurements of light reflected from the crop canopy at key wavelengths indicative of plant vigor. Relative differences in vigor 10

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among plants in the same field can be captured by comparing canopy reflectance measurements like NDVI and NDRE. We have been using handheld devices, drones and satellite imagery at our demonstration sites to compare crop reflectance values in the N-rich zones and the broader field. One of the tools we are using is the GreenSeeker by Trimble Agriculture. This is a hand-held NDVI meter (See Figure 1) that emits light and detects how much is reflected from the crop canopy in the red and infrared wavelengths. The GreenSeeker’s canopy measurement indicates how well the plants are growing and covering the soil with greenness. This information about vigor is important early in the crop’s growth because it indicates the ability of plants to support grain production and yield potential. We are obtaining similar information as from the GreenSeeker by measuring NDRE with a five-band multispectral

March / April 2021

camera (MicaSense RedEdge-MX) mounted on a drone (DJI Matrice M200 V2). NDRE is similar to NDVI but replaces the reflectance from the red wavelength with reflectance from the red edge wavelength. Because the drone is able to capture data from hundreds of feet above the ground, it allows us to measure a large area quickly and under conditions when entering the field is not possible. Figure 2 depicts side-by-side images from a field in Solano County where N-rich reference zones were implemented during the 2019-20 season. Another device we are using to monitor plant N is the atLEAF CHL by FT Green LLC, which is a chlorophyll meter that measures light absorbed by a single leaf (Figure 3). Like the GreenSeeker, it also emits and detects light. The atLEAF CHL, however, measures how much light passes through a single leaf instead of measuring reflected light. This information becomes increasingly valuable as an indicator of whether or not the crop has sufficient N as it begins heading out and filling grain. Step-by-step instructions for using both the GreenSeeker and atLEAF CHL in small grains are available at ucanr.edu/blogs/blogcore/postdetail. cfm?postnum=42903. Since plant N is strongly related to plant greenness and chlorophyll content, measurements of NDVI,

NDRE and leaf chlorophyll can serve as proxies for relative plant N status within a field. Many factors can affect absolute greenness or chlorophyll values, including variety, crop injury and environmental factors. Because of this, it is important to remember that the absolute values given by these devices are only meaningful when compared to a reference zone like the N-rich zone.

SI Value Range

SI Category

Plant N Status

> 0.95

High

Sufficient

0.95 – 0.80

Medium

Deficient

< 0.80

Low

Highly Deficient

Table 2. Sufficiency Index (SI) values and associated plant N sufficiency status, calculated as the production area value divided by the N-rich zone value.

What do the Readings Mean?

Plant reflectance and transmittance measurements are best interpreted by expressing values measured in the broader field relative to the N-rich reference zones, according to the following equation: Relative value= (Production area value)/(N-rich zone value)

The relative value is sometimes referred to as a Sufficiency Index (SI) and will usually result in a decimal value between 0 and 1. When the SI is below a certain threshold, it indicates that the production area is experiencing detectable N deficiency relative to the N-rich zone. Table 2 shows SI ranges for proximal and remotely-sensed data and the associated plant N status.

Summary

California farmers are under pressure to increase N use efficiency and reduce the potential for N loss to the environment. N-rich reference zones are a tool that can assist in these goals while considering and managing the risk of reduced yields. By implementing N-rich reference zones, using a suite of tools to monitor them during the season and comparing results to the broader field, a grower gets real-time knowledge to inform N fertilizer management in small grains. The informa-

tion gained from implementing N-rich reference zones can help growers make fertilizer applications when increased yield and/or protein benefits are likely and avoid them when they are not. These improvements in N fertilizer decision-making can yield better economic and environmental outcomes in California small grain systems. Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com Ceres Imaging delivers irrigation management solutions to improve profitability across your operation.

When it comes to deciding on N fertilization in California small grains, a N fertilizer response is almost certain when plant N status is “Highly Deficient”, very likely when the status is “Deficient” and uncertain when the status is “Sufficient”. The SNQT supplements the plant measurements with information about the current nitrate concentration in the root zone. If a grower decides that a N fertilizer application is warranted based on the combination of plant and soil measurements, the next step is to figure how much N is necessary. This can be determined using a crop growth and N uptake model in conjunction with yield and protein goals. As part of our larger demonstration project, we will be releasing an online decision support tool in 2021 that integrates these components and provides customized predictions of crop response to in-season N fertilizer.

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A REVIEW OF PYTHIUM DISEASES IN ROW CROPS Soilborne Organism is Known for Causing Seedling Diseases and Other Issues By STEVEN KOIKE | TriCal Diagnostics

phytes and only grow on dead and decaying organic material. Pythium species are mostly found in soil environments but are also present in aquatic habitats.

t is highly likely that growers, PCAs and other field professionals are familiar with the word “Pythium”. Pythium is the name of a soilborne, fungus-like organism that is notorious for primarily causing seedling diseases. Pythium is notable because many row crops are susceptible to it, the pathogen is very widely distributed and occurs in most cropped ground, and despite the use of IPM tools and strategies, Pythium problems can still show up in row crop production systems.

What is Pythium?

Large, established cauliflower plants can still become infected with Pythium (left), resulting in loss of roots, severe stunting and yield loss (all photos courtesy S. Koike.)

Pythium is a fungus-like organism. Previously considered to be a true fungus, molecular studies in recent years indicate that Pythium—as well as closely related organisms like Phytophthora and downy mildew—is more closely related to brown algae and diatoms. Formally, therefore, Pythium species are no longer part of the fungal taxonomic group but are classified in the kingdom Chromista, or Stramenopila. The Pythium genus contains over 200 species, most of which are not plant pathogens. There are Pythium species that are pathogens of animals (some of which can infect humans), and many species are sapro-

Plant pathogenic Pythium species are well equipped to cause problems on row crops. Most of these species form resilient, thick-walled sexual The primary symptom of Pythium diseases is the dark spores (oospores) that can discoloration and decay of roots, pictured here on withstand periods of unfavorlettuce. able dry and warm conditions. These structures enable Pythium to persist in the soil for a long and root-to-root. time. When favorable soil conditions are present, mostly in the form of abun- Diverse Pythium Diseases dant soil water, these Pythium organIn contrast to many plant pathogens, isms either produce hyphae that grow Pythium causes several different types toward the roots or swimming spores of problems on crops (Table 1, see page (zoospores) that move through the soil 14). First, Pythium is a seed pathogen. water in search of susceptible plant Once placed in the ground, seed can tissues. Another feature that makes be exposed to Pythium that is residing Pythium problematic for growers is the in the soil. If conditions are favorable extremely fast growth rate of these orfor the pathogen, Pythium can invade ganisms. Given suitable soil conditions, and colonize the seed, causing it to Pythium pathogens can rapidly grow rot before it can germinate. If the seed from seed-to-seed, seedling-to-seedling germinates, Pythium can cause a decay

Continued on Page 14 12

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March / April 2021

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PYTHIUM DISEASE CATEGORY

TARGETED PLANT TISSUE

Seed decay

Seed planted in the ground is invaded and rotted before the seed germinates.

Pre-emergent damping-off

Seed germinates; root and shoot are infected and killed before seedling shoot emerges above the ground.

Post-emergent damping-off

Seed germinates; root and shoot are infected but seedling shoot is able to emerge above ground before collapsing and dying.

Root and crown rot of young plants

Young plants are healthy while germinating and emerging; after plant establishment, roots or crowns become infected.

Root rot of mature plants

Roots of mature plants can become infected later in crop development. This results in “root pruning” and subsequent reduction in growth, vigor, and yield.

Foliar blight

Above ground leaves, stems, shoots become diseased when the pathogen is splashed up onto foliage.

Vegetable soft rot

Fleshy vegetables such as cucurbit fruits, sweet potato roots, and potato tubers develop soft decays.

Table 1. Categories of Pythium diseases of row crops

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Continued from Page 12 of the roots and shoots that just grew out of the seed. This early disease stage is often called damping-off. Damping-off is further divided into two phases. If the newly germinated seedling is infected so early and so severely that it dies before being able to break through the soil surface, this situation is called pre-emergent damping-off. However, post-emergent damping-off occurs if the diseased seedling is strong enough to emerge above the soil surface, only to succumb and collapse shortly afterwards. Collectively, seed decay, pre-emergent damping-off, and post-emergent damping-off can result in loss of plants very early in the production cycle, causing stand loss in the field. Healthy seedlings that escape death at the seed and newly germinated stages remain vulnerable to this pathogen; established seedlings can still be infected and become stunted and die due to diseased roots and crowns. Older, established plants have escaped the damping-off phase that kills seedlings but can be subject to infections that prune back the roots, leading to reduced plant vigor and yield. For example, Pythium can cause late infections in cauliflower and result in weakened roots and poorly yielding plants. This soilborne pathogen can even cause a foliar blight of leaves and shoots, though this type of disease is not very common. Bits of soil carrying Pythium can be splashed or moved up onto foliage and cause blights on crops such as spinach and bean. Finally, the fleshy parts of some vegetable crops are subject to Pythium pathogens. If in contact with infested soil, cucurbit

March / April 2021

Pythium pathogens form thick-walled oospores that enable the pathogen to survive in soil for prolonged periods.

fruits, sweet potato storage roots and potato tubers can develop a soft, watery rot that will result in a non-marketable commodity. Of the hundreds of Pythium species worldwide, relatively few species infect row crops. These plant pathogens can be conveniently placed into two categories. One group consists of Pythium

When sufficient soil water is present, Pythium forms swimming spores that are released and search for host roots. Pictured here is a cluster of zoospores just prior to release.

species that have a relatively narrow host range and infect only a few crops, with those few crops tending to mostly be within a particular plant family. Examples are Pythium mastophorum, which primarily infects celery and parsley (Apiaceae family), and Pythium uncinulatum, which reportedly only causes significant disease on lettuce (Table 2, see page 16). The second

group contains Pythium organisms that have very large host ranges. The two main species, P. aphanidermatum and P. ultimum, both infect scores of plants, including dozens of vegetable and row crops.

Continued on Page 16

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Pythium species

Reported row crop hosts

P. aphanidermatum

bean, beet, cabbage, carrot, cauliflower, cucumber, eggplant, lettuce, melon, onion, parsley, pea, pepper, potato, radish, spinach, sweet potato, tomato, watermelon

P. irregulare

asparagus, basil, bean, beet, Brussels sprouts, cabbage, carrot, cauliflower, celery, cilantro, cucumber, eggplant, endive, lettuce, melon, onion, parsley, pea, pepper, potato, radish, spinach, sweet potato, tomato, watermelon

P. mastophorum

celery, parsley

P. polymastum

broccoli, cabbage, cauliflower

P. sulcatum

carrot( infects other crops but causes few symptoms)

P. ultimum

bean, beet, Brussels sprouts, cabbage, carrot, cauliflower, celery, cilantro, cucumber, eggplant, endive, leek, lettuce, melon, onion, pea, pepper, potato, radish, spinach, sweet potato, tomato, watermelon

P. uncinulatum

lettuce

P. violae

carrot( infects other crops but causes few symptoms)

Table 2. Examples of Pythium pathogens with broad vs. narrow host ranges

Continued from Page 15

"Fertigation delivers fertilizer to active roots. As long as irrigation is managed to deliver only needed water, fertigation can be a highly efficient method of fertilization."

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Disease Development

Diagnostic Considerations

Pythium is not the only soilborne pathogen that causes seedling damping-off and root rots of row crops. On spinach, damping-off and root rot can be caused by both Pythium and Fusarium; visually, one cannot distinguish between the symptoms caused by these two pathogens. Pythium and Phytophthora pathogens both cause dark, discolored roots of lettuce and cannot be differentiated in the field. Cauliflower transplants are susceptible to both Pythium and Rhizoctonia pathogens, both of which caused the roots to become

Development of Pythium diseases is straightforward. Initial inoculum is almost always linked with infested field soils and associated soil water. Pythium is a soilborne pathogen that resides in the soil primarily as dormant resting structures. Pythium inoculum is not seedborne or airborne. For Pythium to become active, grow, and produce those swimming zoospores, the soil must be wet for prolonged periods. Once susceptible seed, seedlings, and other plant parts are in close contact with Pythium inoculum, infection can take place and disease will be initiated. If wet soil conditions persist and temperatures are optimum for the pathogen, disease losses can Pythium plant pathogens can grow very rapidly. Pictured here are be significant. three-day-old cultures of Pythium, Phytophthora, Fusarium and Verticillium. The diameter of the petri dish is 85 mm.

March / April 2021

N AV E L O R A N G E WO R M M A N AG E M E NT discolored. Precise and accurate diagnosis of Pythium diseases will therefore require lab-based tests and assays.

Managing Pythium

Controlling diseases caused by Pythium requires the implementation of IPM practices. Site selection: Choose to plant in fields that do not have a history of Pythium problems and have well-draining soils. Crop rotation: If Pythium is an issue, avoid planting the same susceptible crop in the infested field. Rotate to crops that are not known to be susceptible to the Pythium species present at that location. However, remember that some Pythium species have very broad host ranges (Table 2).

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Irrigation management: Because the Pythium pathogen is so strongly dependent on wet soil conditions, carefully schedule and limit irrigations to prevent overwatered, saturated soils. Time of planting: In some cases, moving the planting date to a different time of year may help reduce losses to Pythium. For example, depending on the Pythium species of concern, planting the crop in the warmer, drier summer may be preferred to seeding the crop in the cooler, wetter spring. Fungicides: Plant seed treated with a fungicide that is active against Pythium. Note that the fungicides used to control Rhizoctonia or Fusarium have no effect on Pythium. For some crops, applying fungicides to the emergent crop may provide additional protection. The repeated use of products having the same mode of action can result in Pythium isolates that are insensitive (=resistant) to those products; therefore, IPM strategies will require that thought be given to deploying different fungicides. Resistant or tolerant cultivars: Unfortunately, there do not appear to be any row crop cultivars that have genetic resistance to Pythium. Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

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Plastic Mulches Reduce Spotted-Wing Drosophila Infestation in Fall-Bearing Raspberry By HANNA MCINTOSH | University of Wisconsin, Madison CHRISTELLE GUÉDOT | University of Wisconsin, Madison AMAYA ATUCHA | University of Wisconsin, Madison

potted-wing drosophila (SWD), Drosophila suzukii, is an invasive vinegar fly and a major pest of softskinned fruit crops. The fly was first detected in the continental U.S. in 20081 and has quickly spread from its native range in Eastern Asia throughout the U.S. and into most major fruit-producing regions of the world2. For smallscale fruit growers, damage from this pest substantially reduces the yield of marketable fruit, making susceptible crops challenging to grow economically and sustainably3,4. For large-scale growers, the presence of SWD can lead to complete crop loss due to processors’ zero-tolerance policies for insect infestation5.

Biology

Vinegar flies typically lay their eggs in damaged or rotting fruit, but female SWD have a highly serrated ovipositor that allows them to saw through the skin of undamaged, ripening fruit6,7, which makes SWD an especially detrimental pest. Larvae emerge inside of and feed on the fruit, making it mushy and unmarketable. Recent research showed that around 80% of larvae drop from the fruit to pupate in the top layer of soil and that they are more likely to drop from the fruit if the fruit is overcrowded8,9. Larvae and pupae can also reach the ground when damaged fruit becomes mushy and falls to the ground. SWD has a quick generation time, with many generations per year in most regions. The fly develops fastest in temperatures between 68 to 83 degrees F, but is unable to develop at temperatures above about 87 degrees F10,11. In temperate regions like the Upper Midwest or Pacific Northwest, SWD populations are highest during summer months. In hotter regions like California or Florida, fly populations are highest in the spring and fall and are much lower during their hot and dry summer months12.

Spotted-wing drosophila life cycle (courtesy Jana Lee, USDA-ARS.)

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SWD thrives in high humidity, developing fastest around 94% humidity13. Researchers found that females laid more eggs in

March / April 2021

the inner canopy of blackberry and blueberry plants, likely because the environment is more humid, cooler and darker14,15. Fruit crops that are the most susceptible to SWD include raspberries, blackberries, blueberries, strawberries, sweet and tart cherries, and some cultivars of wine grapes16-18. However, SWD can survive on alternative hosts like wild blackberries and apples, buckthorn and honeysuckle. It remains largely unknown how SWD survive in the winter and spring before fruit is available in the landscape and on farms, but one study found that SWD can develop on non-fruit hosts like mushrooms and bird manure19.

Traditional Management

Pest pressure from SWD is often very high due to the fly’s fast development time, optimal development conditions in the summer and high availability of host plants and food in the agroecosystem. Management relies heavily on chemical control in organic and conventional systems, which is costly to growers. In California, chemical controls for SWD cost around $470/ acre for conventional and $1,210/acre for organic growers3. Only a few insecticides approved for use in organic systems are effective at controlling SWD, limiting organic growers’ options for control20. Unfortunately, recent reports show evidence of insecticide resistance developing

Growers have used plastic mulches since the 1960s to modify the microclimate in fruit and vegetable agroecosystems. Plastic mulches are commonly used for weed control, promoting earlier ripening, improving fruit quality or color and increasing yield25,26. Different colors of plastic mulches have also been shown to successfully control

Continued on Page 20

Spock

Luigi

Since SWD is sensitive to temperature and humidity, cultural practices that modify the crop canopy microclimate have the potential to reduce infestation by deterring adults from laying eggs or disrupting larval development inside of fruit. Management strategies for SWD typically target adult flies in the canopy, but since the majority of SWD larvae fall to the ground before pupation, ground-based cultural management practices could also be important for reducing populations.

Robin

Cultural practices can help reduce the fly’s population and are often used in tandem with chemical controls. Such practices include harvesting fruit promptly (every one to two days), frequent field sanitation, burial or composting of infested fruit and exclusion netting23,24. However, these methods are labor-intensive and expensive.

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for some active ingredients in some regions, including spinosad (the main insecticide used to control SWD in organic systems)21,22.

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(Left) Spotted-wing drosophila adult female and male on a raspberry. Male flies are easy to identify by the large black spots on their wings. (Right) Spotted-wing drosophila females have a serrated ovipositor that allows them to lay eggs in undamaged, ripening fruit (photos courtesy Agri-Mag and Chris Thomas.)

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Continued from Page 19

fall-bearing raspberries.

insect pests including aphids, whiteflies, In this study, we tested black and whiteAsian citrus psyllid and Mexican bean on-black biodegradable plastic mulches beetles27-30. (Organix Solutions AG film), metallic polyethylene mulch (Imaflex SHINE N’ Plastic Mulches for SWD RIPE) and a grower-standard control Based on the extensive body of literawhere grass filled in the space between ture reporting that plastic mulches can the alleyway and the raspberry plants. modify the crop microclimate, control We assessed the three mulches’ impact some insect pests and provide other on SWD adult and larval populations horticultural benefits, we tested the im- in fall-bearing raspberry. pact of three colors of plastic mulches on SWD adult and larval populations. We laid the mulches by hand when the Our study was conducted in 2019 and raspberry canes were just emerging 2020 on a small fruit and vegetable from the soil in late April. We laid two farm in South Central Wisconsin in mulch strips (25 feet long by 2.3 feet

wide) along each side of the row, leaving a six-inch gap between the strips for the canes to grow. The edges of the mulches were secured with biodegradable sod stakes. All four treatments were randomly distributed in each of four rows of fall-bearing raspberries (cultivars “Polana” and “Caroline”), totaling 16 plots. Starting when the first flies were detected in June, we measured the adult SWD populations passively using clear sticky cards placed in the fruiting zone, which were replaced weekly to estimate fly populations by week. Larval infestation of fruit was evaluated by counting the number of larvae using the salt float method31. The evaluations were done two to four times per month starting in August. Adult and larval populations were measured throughout the season until adult populations reached zero, usually in mid-October. We also did a preliminary experiment to test whether plastic mulches could kill larvae that fell onto the mulch surface. We put lab-reared larvae into ‘corrals’ made from plastic sandwich containers and recorded their mortality and movement over three hours.

Population Reductions

In both years of our study, we found significantly lower SWD populations above all three plastic mulches compared to the control plots. Over the two-year period, the black and metallic mulches reduced the adult population of SWD by 51% and the white mulch reduced flies by 42% compared to the control.

Experimental plots of plastic mulches in fall-bearing raspberries in Wisconsin (photo by H. McIntosh.)

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March / April 2021

Interestingly, the plastic mulches only reduced female fly populations and did not impact the number of male flies caught on the sticky cards. With fewer female flies in the canopy above the plastic mulches, it was unsurprising that we also found fewer larvae infesting the fruit in the mulched plots. Over the two-year study, the black mulch

decreased the number of larvae in fruit by 72%, the metallic mulch by 61%, and the white mulch by 52% compared to the control. Plastic mulches may be more effective than other types of mulches tested for managing SWD. In our study, we recorded the lowest adult fly populations and larval infestation of fruit above the black plastic mulch. A 2019 study tested black fabric weedmat as a cultural control for SWD in blueberry in several states and found no effect of the weedmat on SWD infestation of blueberries32. It is possible that some quality of the plastic mulch material (such as reflectivity or lack of permeability) makes it more deterrent to SWD than the weedmat. In our preliminary experiment, larvae placed on the plastic mulches died quickly. Larvae on the black mulch died in less than one hour, and larvae on the white and metallic mulches died in less than three hours. We recorded high surface temperatures on the mulches, with all mulches heating up above 87 degrees F (SWD’s threshold for development) for two to four hours each day. On hot days, the black mulch got above 150 degrees F.

‘Corrals’ made from plastic sandwich containers used to test mortality of larvae on the mulch surface (photo by H. McIntosh.)

When placed on the mulch, we observed larvae struggling to crawl and visibly desiccating within minutes, making it unlikely that larvae could crawl off the mulch into the safety of the soil. We will collect more data in summer 2021 to confirm these promising results. The results of our study provide evidence that black, white and metallic plastic mulches can reduce SWD adult and larval populations in fall-bearing raspberry in the Upper Midwest, showing promise for use of plastic mulches in sustainable pest management. Combining plastic mulches with other cultural practices including short harvest intervals (every one to two days) and frequent field sanitation could have an additive effect on reducing SWD populations, potentially reducing the need for chemical controls in conventional and organic cropping systems.

Next Steps

Although the use of plastic mulches reduces SWD populations in the canopy of raspberry plants, the specific mechanisms causing this reduction are still unknown. We are still investigating how canopy light conditions, temperature and humidity are influenced by the plastic mulches and whether these factors can explain the reduction in SWD populations we measured.

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Continued from Page 21 In the next two years of this project, we will conduct field experiments to determine whether the three plastic mulches we tested influence beneficial insects, including pollinators, and how the mulches impact soil health, raspberry plant growth, fruit quality and yield in Wisconsin’s climate.

Testing these mulches in other regions and fruit crops is warranted to determine if the reduction of SWD is maintained in different climates and other susceptible crops. Overall, plastic mulches are a promising new tool for more sustainable management of SWD in raspberry in the Upper Midwest. References

1. Hauser, M. A historic account of the invasion of Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) in the continental United States, with remarks on their identification. Pest Manag. Sci. 2011, 67, 1352–1357, doi:10.1002/ps.2265. 2. CABI Drosophila suzukii (spotted wing drosophila); 2016; 3. Farnsworth, D.; Hamby, K.A.; Bolda, M.; Goodhue, R.E.; Williams, J.C.; Zalom, F.G. Economic analysis of revenue losses and control costs associated with the spotted wing drosophila, Drosophila suzukii (Matsumura), in the California raspberry industry. Pest Manag. Sci. 2017, 73, 1083–1090, doi:10.1002/ps.4497. 4. DiGiacomo, G.; Hadrich, J.; Hutchison, W.D.; Peterson, H.; Rogers, M. Economic Impact of Spotted Wing Drosophila (Diptera: Drosophilidae) Yield Loss on Minnesota Raspberry Farms: A Grower Survey. J. Integr. Pest Manag. 2019, 10, doi:10.1093/jipm/pmz006. 5. Bruck, D.J.; Bolda, M.; Tanigoshi, L.; Klick, J.; Kleiber, J.; Defrancesco, J.; Gerdeman, B.; Spitler, H. Laboratory and field comparisons of insecticides to reduce infestation of Drosophila suzukii in berry crops. Pest Manag. Sci. 2011, 67, 1375–1385, doi:10.1002/ps.2242. 6. Kanzawa, T. Studies on Drosophila suzukii Mats. J. Plant Prot. 1939, 23, 66–70, 127–132, 183–191. 7. Walsh, D.B.; Bolda, M.P.; Goodhue, R.E.; Dreves, A.J.; Lee, J.; Bruck, D.J.; Walton, V.M.; O’Neal, S.D.; Zalom, F.G. Drosophila suzukii (Diptera: Drosophilidae): Invasive Pest of Ripening Soft Fruit Expanding its Geographic Range and Damage Potential. J. Integr. Pest Manag. 2011, 2, G1–G7, doi:10.1603/ipm10010.

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Management strategies for SWD typically target adult flies in the canopy, but since the majority of SWD larvae fall to the ground before pupation, ground-based cultural management practices could also be important for reducing populations. 8. Woltz, J.M.; Lee, J.C. Pupation behavior and larval and pupal biocontrol of Drosophila suzukii in the field. Biol. Control 2017, 110, 62–69, doi:10.1016/j.biocontrol.2017.04.007. 9. Bezerra Da Silva, C.S.; Park, K.R.; Blood, R.A.; Walton, V.M. Intraspecific Competition Affects the Pupation Behavior of Spotted-Wing Drosophila (Drosophila suzukii). Sci. Rep. 2019, 9, 7775, doi:10.1038/s41598-019-44248-6. 10. Ryan, G.D.; Emiljanowicz, L.; Wilkinson, F.; Kornya, M.; Newman, J.A. Thermal tolerances of the spotted-wing drosophila drosophila suzukii (Diptera: Drosophilidae). J. Econ. Entomol. 2016, 109, 746–752, doi:10.1093/jee/tow006. 11. Hamby, K.A.; E. Bellamy, D.; Chiu, J.C.; Lee, J.C.; Walton, V.M.; Wiman, N.G.; York, R.M.; Biondi, A. Biotic and abiotic factors impacting development, behavior, phenology, and reproductive biology of Drosophila suzukii. J. Pest Sci. (2004). 2016, 89, 605–619. 12. Wang, X.G.; Stewart, T.J.; Biondi, A.; Chavez, B.A.; Ingels, C.; Caprile, J.; Grant, J.A.; Walton, V.M.; Daane, K.M. Population dynamics and ecology of Drosophila suzukii in Central California. J. Pest Sci. (2004). 2016, 89, 701–712, doi:10.1007/ s10340-016-0747-6. 13. Tochen, S.; Woltz, J.M.; Dalton, D.T.; Lee, J.C.; Wiman, N.G.; Walton, V.M. Humidity affects populations of Drosophila suzukii (Diptera: Drosophilidae) in blueberry. J. Appl. Entomol. 2016, 140, 47–57, doi:10.1111/jen.12247. 14. Diepenbrock, L.M.; Burrack, H.J. Variation of within-crop microhabitat use by Drosophila suzukii (Diptera: Drosophilidae) in blackberry. J. Appl. Entomol. 2017, 141, 1–7, doi:10.1111/jen.12335. 15. Evans, R.K.; Toews, M.D.; Sial, A.A. Diel periodicity of Drosophila suzukii (Diptera: Drosophilidae) under field conditions. PLoS One 2017, 12, doi:10.1371/journal.pone.0171718. 16. Lee, J.C.; Bruck, D.J.; Curry, H.; Edwards, D.; Haviland, D.R.; Van Steenwyk, R.A.; Yorgey, B.M. The susceptibility of small fruits and cherries to the spotted-wing drosophila, Drosophila suzukii. Pest Manag. Sci. 2011, 67, 1358–1367, doi:10.1002/ ps.2225. 17. Kamiyama, M.T.; Guedot, C. Varietal and Developmental Susceptibility of Tart Cherry (Rosales: Rosaceae) to Drosophila suzukii (Diptera: Drosophilidae). J. Econ. Entomol. 2019, 112, 1789–1797, doi:10.1093/jee/toz102. 18. Pelton, E.; Gratton, C.; Guédot, C. Susceptibility of cold hardy grapes to Drosophila suzukii (Diptera: Drosophilidae). J. Appl. Entomol. 2017, 141, 644–652, doi:10.1111/jen.12384. 19. Stockton, D.G.; Brown, R.; Loeb, G.M. Not berry hungry? Discovering the hidden food sources of a small fruit specialist, Drosophila suzukii. Ecol. Entomol. 2019, een.12766, doi:10.1111/een.12766. 20. Sial, A.A.; Roubos, C.R.; Gautam, B.K.; Fanning, P.D.; Van Timmeren, S.; Spies, J.; Petran, A.; Rogers, M.A.; Liburd, O.E.; Little, B.A.; et al. Evaluation of organic insecticides for management

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of spotted-wing drosophila (Drosophila suzukii) in berry crops. J. Appl. Entomol. 2019, 143, 593–608, doi:10.1111/jen.12629. 21. Gress, B.E.; Zalom, F.G. Identification and risk assessment of spinosad resistance in a California population of Drosophila suzukii. Pest Manag. Sci. 2019, 75, 1270–1276, doi:10.1002/ps.5240. 22. Van Timmeren, S.; Mota-Sanchez, D.; Wise, J.C.; Isaacs, R. Baseline susceptibility of spotted wing Drosophila (Drosophila suzukii) to four key insecticide classes. Pest Manag. Sci. 2018, 74, 78–87, doi:10.1002/ps.4702. 23. Leach, H.; Van Timmeren, S.; Isaacs, R. Exclusion Netting Delays and Reduces Drosophila suzukii (Diptera: Drosophilidae) Infestation in Raspberries. J. Econ. Entomol. 2016, 109, 2151–2158, doi:10.1093/jee/tow157. 24. Leach, H.; Moses, J.; Hanson, E.; Fanning, P.; Isaacs, R. Rapid harvest schedules and fruit removal as non-chemical approaches for managing spotted wing Drosophila. J. Pest Sci. (2004). 2018, 91, 219–226, doi:10.1007/s10340-017-0873-9. 25. Tarara, J. Microclimate modification with plastic mulch. HortScience 2000, 35. 26. Kasirajan, S.; Ngouajio, M. Polyethylene and biodegradable mulches for agricultural applications: A review. Agron. Sustain. Dev. 2012, 32, 501–529, doi:10.1007/s13593-011-0068-3. 27. Greer, L.; Dole, J.M. Aluminum foil, aluminium-painted, plastic, and degradable mulches increase yields and decrease insect-vectored viral diseases of vegetables. Horttechnology 2003, 13, 276–284. 28. Croxton, S.D.; Stansly, P.A. Metalized polyethylene mulch to repel Asian citrus psyllid, slow spread of huanglongbing and improve growth of new citrus plantings. Pest Manag. Sci. 2014, 70, 318–323, doi:10.1002/ps.3566. 29. Nottingham, L.B.; Kuhar, T.P. Reflective Polyethylene Mulch Reduces Mexican Bean Beetle (Coleoptera: Coccinellidae) Densities and Damage in Snap Beans. J. Econ. Entomol. 2016, 109, 1785–1792, doi:10.1093/jee/tow144. 30. Nottingham, L.B.; Beers, E.H. Management of Pear Psylla (Hemiptera: Psyllidae) Using Reflective Plastic Mulch. J. Econ. Entomol. 2020, doi:10.1093/ jee/toaa241. 31. Dreves, A.; Cave, A.; Lee, J. A Detailed Guide for Testing Fruit for the Presence of Spotted Wing Drosophila (SWD) Larvae. Oregon State Univ. Ext. Serv. 2014, EM 9096, 1–9. 32. Rendon, D.; Hamby, K.A.; Arsenault-Benoit, A.L.; Taylor, C.M.; Evans, R.K.; Roubos, C.R.; Sial, A.A.; Rogers, M.; Petran, A.; Van Timmeren, S.; et al. Mulching as a cultural control strategy for Drosophila suzukii in blueberry . Pest Manag. Sci. 2019, doi:10.1002/ps.5512.

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New Findings on Limb Dieback of Figs in California Pruning Practices Can Help Protect from Disease Pathogen

By THEMIS J. MICHAILIDES | Plant Pathologist, UC Davis/Kearney Agricultural Research and Extension Center DAVID MORGAN | Staff Research Associate, UC Kearney Agricultural Research and Extension Center and GIORGIO GUSELLA | Graduate Student in Plant Pathology, University of Catania, Italy

ack in 2004, and again in recent years, there were concerns by fig growers mainly in Madera and Merced counties about an excessive killing of major branches of their fig trees (Figure 1). Visits to some orchards back then and recently indicated that indeed they had a major problem. Initial close examinations of the dead branches showed symptoms which were similar to another disease: branch wilt of walnut.

The bark of dead fig branches had cracks and one could easily remove large pieces of the bark, exposing the woody tissues underneath which were covered by a black powder. Rubbing this black powder with your finger could easily remove masses of it (Figure 2, see page 25). The inner surface of the broken and removed bark pieces were also black due to these powder masses. A lot of trees had many dead major branches while others had one or two dead along with other branches bearing chlorotic and thin canopy, distinct from the green and dense canopy of healthy branches.

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Figure 1. Left, Fig tree affected by severe limb dieback; top right, still active canker; bottom right, inactive canker (branch is dead) (all photos courtesy G. Gusella.)

Pathogen Activity Slices of these woody tissues from the To collect samples, we cut some of the branches were taken, isolations were symptomatic branches close to the made in the laboratory and a fungus interface of dead and alive-looking known to be a pathogen of woody (green) tissues. We noticed that in a tissues was consistently recovered. cross section, the dead woody tissues The name of this pathogen is Neoscywere delineated from the healthy tistalidium dimidiatum, which is a new sues by a dark brown line while the liv- taxonomic name of Hendersonula ing woody tissues were white (Figure 1). toruloidea fungus, which represents the pathogen first reported to cause the

March / April 2021

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Figure 2. Top, Neoscytalidium dimitiatum, the cause of limb dieback producing spores (arthrospores) as the mycelia dried up and separate to small segments under the bark; bottom, easily rubbing off the spores under the bark (photo courtesy Beth Teviotdale.)

branch wilt disease of walnut. Checking the literature, the same fungus under a different name (i.e. Nattrassia mangifera) was reported in 1945 on commercial figs in California as well as on Ficus religiosa and Ficus bengalensis, causing dieback and trunk cankers. In addition to walnut branch wilt, which is a common disease of walnuts grown in the San Joaquin Valley, the same fungus was reported in causing branch wilt and dieback of poplar, eucalyptus and mango. In other reports, we found out that this pathogen can cause killing of major branches of walnut, ash trees and grapefruit. More recently, it has been reported causing cankers and hull rot of almond. On fig shoots, the pathogen grows and infects injured bark (i.e. mechanical wounds, wounds by hail or sunburn), invades the woody tissues and kills the branch. When the branch is killed, it dries and usually the bark cracks, exposing large

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Figure 3. Left, pycnidia protruding through bark cracks; right, arthrospores of Neoscytalidium dimidiatum causing limb dieback of fig.

Survey of Affected Areas

Continued from Page 25 masses of black spores. These are not true spores but are small segments of mycelia that become black as the tissues dry up and break down into small pieces, producing a layer of black powder under the bark. The fungus also produces pycnidia that protrude through small cracks of the bark (See Figure 3). However, it is the spores produced in masses by the breaking mycelia called arthrospores. that can be spread readily by air and/or splashing rain and can cause infections of pruning wounds and other injuries of branches.

Before doing pathogenicity studies with the Neoscytalidium fungus, we wanted to make sure that this fungus was found frequently throughout the area where fig trees showed similar symptoms to the ones we initially observed in Madera County. Therefore, a survey of 16 fig orchards with branch dieback symptoms, representing all the major fig varieties (Black Mission, Calimyrna, Conadria and the male trees (Roeding and Stanford caprifig varieties)) was done in Fresno, Madera and Kern counties. Neoscytalidium was isolated in all of these orchards.

Continued on Page 28

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Figure 4. Susceptibility of various fig cultivars to limb dieback pathogen Neoscytalidium dimidiatum.

Dr. Themis Michailides sampling symptomatic fig trees.

Continued from Page 26

Figure 5. Effect of stress factors (mallet wounding and sunburn) and treatment with white wash affecting the severity of limb dieback of fig.

Limb and branch samples from the majority of these orchards had 60% to 100% Neoscytalidium, while three had 7% to 11%, and two 26% to 32%. In 12 of these orchards, a second pathogen, Phomopsis spp., was isolated along with Neoscytalidium in the first year of the survey. Phomopsis sinarencis has been reported in California causing an epidemic on Kadota figs back in 1935 and in other countries as an important fig canker pathogen. By the third year of this survey, less Phomopsis was isolated, and, very recently, almost none was isolated, probably because the very susceptible Kadota variety is rarely now planted in California. Phomopsis is known as a pathogen fungus associated with canker diseases in many other crops around the world, but more investigations are needed to figure out its role in fig limb dieback.

Differences in Susceptibility

To determine if there were any differences in susceptibility to the limb dieback pathogen, we inoculated six cultivars directly in the field. We found that three months after inoculations, the cultivars Kadota, Black Mission and Sierra developed twice as long canker size than the cultivars Brown Turkey, Calimyrna and Conadria (Figure 4). Growers also reported that they see the problem to be more severe in Black Mission than other cultivars. Inoculations of six cultivars showed that Neoscytalidium is a plant pathogen that likes high temperatures. For instance, it cannot grow below 50 degrees F; its optimum temperature for growth is 90 to 95 degrees F, and it can even grow at 104 degrees F to some extent. Therefore, this fungus likes hot summer temperatures and prefers to infect sunburned branches and pruning wounds.

Figure 6. Effect of Surround® spray on the severity of limb dieback of fig.

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March / April 2021

In experiments, we inoculated shoots of fig of different ages, including current growth (green) shoots, one-year, two-year and threeyear-old shoots, by wounding and inoculating with either a mycelial plug or a spore suspension. Interestingly, the three-year-old shoots

N AV E L OR A NG E WOR M M ON I T O R I NG S Y S T E MS developed almost three-fold larger cankers than the cankers on current and the one-year-old shoots. This suggests that larger cuts in the field during pruning seem to be more susceptible to infection than cuts made in current or one-yearold shoots. Also, inoculations done in May, June and July resulted in larger cankers than those done from August to November. ‘ When we compared infection on pruning wounds done in winter vs. those done in summer, pruning wounds in the summer developed almost threefold larger cankers than those done during winter months. Therefore, it is recommended that pruning of figs should be done in winter when pruning wounds seem to be less susceptible. Figs can be protected from infections of the branch wilt pathogen if shoots are painted with whitewash to protect them from sunburn. Applying Surround® on shoots also protected the shoots from infection, and this is recommended to become a routine practice by fig growers. Figure 5 shows results of inoculation experiments done following various treatments in the field and artificial inoculation with the pathogen.

Although wounding by only mallet or only sunburn resulted in larger canker than the non-inoculated, un-wounded/ un-treated shoots, the shoots that were damaged by mallet wounding and sunburn at the same time resulted in the longest cankers. White wash or spraying with Surround protected the shoots even after wounding with mallets and inoculation (Figure 5 and 6, see page 28). Therefore, pruning that exposes the shoots to sunburn and or any other type of wounding should be avoided, and spraying with Surround will help protect the fig shoots from the limb dieback pathogen. The authors thank the California Fig Institute for funding this research and a number of fig growers who allowed us to sample their orchards.

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Enhancing Diamondback Moth Management with Mating Disruption

By SURENDRA K. DARA | UCCE Entomology and Biologicals Advisor

Brussels sprouts field in Santa Maria (photo by S.K. Dara.)

rassica crops such as broccoli, brussels sprouts, cabbage, canola, cauliflower, collards, kale, kohlrabi, turnip and mustards are important vegetable or oilseed crops. The value of brassica vegetables, also known as cole crops, is more than $1.2 billion in California, which is the leading producer of these crops. Among various arthropod pests that attack brassica crops, the diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae), is of significant importance. Thought to be of European origin, now with worldwide distribution, DBM exclusively feeds on cultivated and weedy crucifers. DBM can have up to 12 generations per year, especially under warmer climate. Female moths deposit 150 eggs on average. Four larval instars feed on foliage and growing parts of young plants or bore into heads or flower buds, resulting in skeletonization of leaves, stunting of the plants or failure of head formation in some hosts. Pupation occurs on the lower surface of leaves or in florets. Adult moths are grayish-brown, and when at rest, a light-colored diamond-shaped pattern can be seen on the upper side of the wings. Farmers typically rely on synthetic and biological insecticidal applications for controlling DBM. Multiple species of 30

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parasitoids and predatory arthropods also provide some control. Due to a heavy reliance on insecticidal control, DBM resistance to several insecticides is a common problem. Resistance of DBM to Bacillus thuringiensis (Ferré et al., 1991), abamectin (Pu et al., 2009), emamectin benzoate, indoxacarb and spinosad (Zhao et al., 2006), pyrethroids and other insecticides (Leibee and Savage, 1992; Endersby et al., 2011) have been reported from around the world. Excessive use of any kind of pesticide leads to resistance problems (Dara, 2020) to an individual pesticide or multiple pesticides. Integrated pest management (IPM) strategy encourages the use of various control options for maintaining pest control efficacy and reducing the risk of resistance development (Dara, 2019). Regularly monitoring pest populations to make treatment decisions, rotating pesticides with different modes of action, exploring the potential of biocontrol agents, and other non-chemical control approaches such as mating disruption with pheromones are some of the IPM strategies for controlling the DBM. While sex pheromones are effectively used to manage several lepidopteran pests and are proven to be a critical IPM tool, mating disruption is not fully explored for controlling DBM. March / April 2021

A study was conducted in Brussels sprouts to evaluate the efficacy of a sprayable pheromone against the DBM and to enhance current IPM strategies.

Methodology

The study was conducted on a 10-acre Brussels sprouts field in Santa Maria. Cultivar Marte was planted in early July for harvesting in December 2020. A typical diamondback control program includes monitoring DBM populations with the help of sticky traps and lures and applying various combinations of biological and synthetic pesticides at regular intervals. This study evaluated the efficacy of adding CheckMate DBM-F to the grower standard practice of monitoring the DBM populations with traps and lures and applying pesticides. Treatments included 1.) grower standard pesticide program (See Table 1) grower standard pesticide program with two applications of 3.1 fl oz of CheckMate DBM-F on August 9 and September 11. Treatment materials were applied by a tractor-mounted sprayer using a 100 gpa spray volume and necessary buffering agents and surfactants. Each treatment was five acres and divided into four quadrants representing four replications. In the middle of each quadrant, one Suterra Wing Trap was set up with a

Date

Trécé Pherocon Diamondback Moth Lure. Lures were replaced once a month in early September and early October. Sticky liners of the traps were replaced every week to count the number of moths trapped. Traps were placed on Aug. 1, 12 and 24, Sept. 1, 11, 18 and 27, and Oct 6, and the moth counts were taken from respective traps on Aug. 8 and 20, Sept. 1, 11, 18 and 27, and Oct. 6 and 15. CheckMate DBM-F was applied at 3.1 fl oz/ac on Aug. 9 and Sept. 11. The number of larvae and their feeding damage on a scale of 0 to 4 (where 0=no damage, 1=light damage, 2=moderate damage, 3=high damage, 4=extensive/irrecoverable) were recorded from 25 random plants within each replication on Aug. 30 and Oct. 6 and 18. Data were subjected to analysis of variance using Statistix software and significant means were separated using Tukey’s HSD test. The retail value of various pesticides was also obtained to compare the cost of treatments. When CheckMate DBM-F[(Z)-11-Hexadecenal (3) , (Z)-11-Hexadecen-1-yl Acetate (1)] was applied the first time on Aug. 9, Dibrom 8 Emulsive was replaced with Warrior II, the buffering agent Quest was not used, and the surfactant Dyne-Amic was replaced with Induce (dimethylpolysiloxane) to avoid potential compatibility issues. The impact of this substitution is expected to be negligible within the scope of this study. The retail cost of 3.1 fl oz CheckMate DBM-F is $45.60. The cost of lures and traps would be about $4 to $8 per acre for a six-month crop like Brussels sprouts.

Results and Discussion

29 July

Buffering agents & Surfactants

Pesticides Crymax (Bacillus thuringiensis subsp. kurstaki) 1 lb (IRAC 11) Proclaim (emamectin benzoate) 4.8 oz (6) Avaunt (indoxacarb) 3.5 oz (22A) Dibrom 8 Emulsive (naled) 1 pt (1B)

Quest (ammonium sulfate, phosphoric acid, and carbamide) buffering agent 1.4 pt

Retail cost $129.04

Dyne-Amic (methyl

esters of C16-C18 fatty acids, polyalkyleneoxide modified polydimethylsiloxane, alkylphenol ethoxylate) organosilicone-based nonionic surfactant

9 August

Crymax 1 lb (11) Radiant SC (spinetoram) 7 fl oz (5) Dibrom 8 Emulsive 1 pt (1B)

Quest 1.2 pt Dyne-Amic 1 pt

$108.51

21 August

Crymax 2 lb (11) Proclaim 4.8 oz (6) Avaunt 3.5 oz (22A) Dibrom 8 Emulsive 1 pt (1B)

Quest 1.2 pt Dyne-Amic 1.2 pt

$145.63

25 August

Dyne-Amic 12 fl oz Crymax 2 lb (11) Radiant SC 7 fl oz (5) Warrior II (lambda-cyhalothrin) 1.8 fl oz (3A)

$93.65

1 September

Crymax 2 lb (11) Dibrom 8 Emulsive 1 pt (1B)

Quest 1 pt Dyne-Amic 12 fl oz

$72.64

4 September

Crymax 2 lb (11) Proclaim 4.8 oz (6) Lannate SP (methomyl) 1 lb (1A) Rimon 0.83EC (novaluron) 10 fl oz (15)

Dyne-Amic 12 fl oz

$138.05

11 September

Crymax 2 lb (11) *Exirel (cyantraniliprole) 20 fl oz (28) Lannate SP 1 lb (1A)

Dyne-Amic 12 fl oz

$146.27

24 September Crymax 2 lb (11) Lannate SP 1 lb (1A) *Movento (spirotetramat) 5 fl oz (23) Radiant SC 7 fl oz (5)

Dyne-Amic 12 fl oz

$171.52

2 October

Dyne-Amic 12 fl oz

$192.17

Crymax 2 lb (11) Avaunt 3. 5 oz (22A)Lannate SP 1 lb (1A) *Movento 5 fl oz (23) Radiant SC 6 fl oz (5)

Crymax 2 lb (11) Dyne-Amic 12 fl oz $78.45 Traps in replication 4 in both treatments 10 15 October Proclaim 4.8 oz (6) on August 8 and replication 1 in the grower standard were missing, probTotal cost $1,275.93 ably knocked down by a tractor. The day before CheckMate DBM-F was first Table 1. Pesticides, buffering agents and surfactants, their active ingredients, rates/ac (along applied, the mean number of adult DMB with the IRAC mode of action groups) and retail pricing for those applied in the grower standard diamondback moth control program. caught was 227 in the grower standard *Applied diamondback moth and aphid control and 271 in the plots that would receive the pheromone application (Figure 1, see page 32). There was a gradual higher in the plots that received Checkthe grower standard before the study but decline in moth counts during the Mate DBM-F. The number of moths were nearly 98% lower by the end of the rest of the observation period in both per trap were about 19% higher in the treatments. However, the decline was pheromone-treated plots compared to Continued on Page 32

March / April 2021

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Diamondback Moth Occurrence

Continued from Page 31

Larval feeding damage ratings were consistently low (P < 0.0001) in the plants that did not receive CheckMate DBM-F (Figure 3). The damage was limited to the older leaves at the bottom of the plants and must have been from early feeding before the initiation of the study. The lack of larvae and the evidence of new feeding damage also confirm that the crop remained healthy and pest-free.

Yield and Cost Comparisons

Since frequent pesticide applications effectively suppressed larval populations and prevented their feeding damage, the effectiveness of mating disruption on larval populations or their damage could not be determined in this study. Moths found in the traps probably developed from the larvae in the field or could have been those that flew in from other areas. However, lower moth populations in CheckMate DBM-F treatment demonstrated the overall influence of mating disruption and pest suppression. It is common to make about 10 to 12 pesticide sprays during the six-month crop cycle of Brussels sprouts. The cost of each application varied from about $73 to $192 depending on the materials used with an average cost of about $128 per application in this study. The cost of two CheckMate DBM-F applications is $91. If diamondback moth populations could be reduced with mating disruption, it is estimated that two to three pesticide applications could be eliminated. That results in $164 to $292 of saving for the pesticide costs and additional savings in the application

Number of moths/traps

The mean number of larvae per 25 plants in a replication was zero on all observation dates except for 0.01 on Aug. 30 in the plots that received CheckMate. Four insecticide applications made by the time the study was initiated and the remaining six applications effectively suppressed larval populations.

Grower Standard

300 250 200 150 100 50 0

0 0 0 20 20 20 20 20 02 0 0 02 02 0 0 2 0 2 2 2 2 2 2 / / / 2 / / / 8 1/ 18 27 20 11/ /6 /15 8/ 9/ 9/ 9/ 8/ 9/ 10 10

Figure 1. Mean number of diamondback moth adults found in the traps.

20.00

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% Control from CheckMate DBM-F

0.00 -20.00 -40.00 -60.00 -80.00 -100.00

0 0 0 0 0 20 0 02 20 02 02 02 02 2 20 02 2 2 2 0 2 / / 2 / / / 20 8/ 11/ 1/2 18 27 /6 /15 8/ 8/ 9/ 9/ 9/ 9/ 10 10

Figure 2. Reduction in moth populations by adding pheromone for mating disruption.

Larval Feeding Damage Grower Standard

GS+CheckMate

1.5

1.0

0.5

0.0

8/30/2020 P < 0.0001

10/6/2020 P < 0.0001

Figure 3. Feeding damage by diamondback moth larvae.

Continued on Page 34 32

GS+CheckMate

Damage Rating

study (Figure 2). The reduction in moth populations from mating disruption was significant on September 18 (P =0.039) and October 15 (P = 0.006).

March / April 2021

10/18/2020 P = 0.0074

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Diamondback moth larva and adult (photos by Jack Kelly Clark, UC IPM.)

Adult diamondback moths on the last observation date in treatments with and without the pheromone (photos by Tamas Zold.)

Feeding damage in cauliflower (photo by S.K. Dara.)

Continued from Page 32 costs per acre by investing $91 in the mating disruption. Since DBM can develop resistance to several chemical and natural pesticides, eliminating some applications as a result of mating disruption also contributes to resistance management along with potential negative impact of pesticides on the environment. Compared to other mating disruption strategies, a sprayable formulation compatible with other agricultural inputs is easier and more cost-effective to use. The grower’s yield data showed 762 cartons/acre from the grower standard block with pesticides alone and 814 cartons/acre from the block that received pesticide and pheromone applications. Although there seems to be a 7% yield difference, since data from individual plots could not be collected for statistical analysis, the impact of DBM mating disruption on yield improvement is inconclusive. This study demonstrated that mating disruption with CheckMate DBM-F will 34

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significantly enhance the current IPM practices by reducing pest populations, contributing to insecticide resistance management, and reducing pest management costs. Additional studies with fewer pesticide applications that allow larvae to survive and cause some damage might further help to understand the role of mating disruption where pest populations are not managed as effectively as in this field. Thanks to the PCA and grower for their research collaboration, Tamas Zold for his technical assistance in data collection, Ingrid Schumann for market research of pesticide pricing and Suterra for the financial support. References Dara, S. K. 2019. The new integrated pest management paradigm for the modern age. J. Int. Pest Manag. 10: 12. Dara, S. K. 2020. Arthropod resistance to biopesticides. Organic Farmer 3 (4): 16-19. Endersby, N. M., K. Viduka, S. W. Baxter, J. Saw, D. G. Heckel, and S. W. McKechnie. 2011. Widespread pyrethroid resistance in Australian diamondback

March / April 2021

moth, Plutella xylostella (L.), is related to multiple mutations in the para soidum channel gene. Bull. Entomol. Res. 101: 393. Ferré, J., M. D., Real, J. Van Rie, S. Jansens, and M. Peferoen. 1991. Resistance to the Bacillus thuringiensis bioinsecticide in a field population of Plutella xylostella is due to a change in a midgut membrane receptor. Proc. Nat. Acad. Sci. 88: 5119-5123. Leibee, G. L. and K. E. Savage. 1992. Evaluation of selected insecticides for control of diamondback moth and cabbage looper in cabbage in Central Florida with observations on insecticide resistance in the diamondback moth. Fla. Entomol. 75: 585591. Pu, X., Y. Yang, S. Wu, and Y. Wu. 2009. Characterisation of abamectin resistance in a field-evolved multiresistant population of Plutella xylostella. Pest Manag. Sci. 66: 371-378. Zhao, J-Z., H. L. Collins, Y-X. Li, R.F.L. Mau, G. D. Thompson, M. Hertlein, J. T. Andaloro, R. Boykin, and A. M. Shelton. 2006. Monitoring of diamondback moth (Lepidoptera: Plutellidae) resistance to spinosad, indoxacarb, and emamectin benzoate. J. Econ. Entomol. 99: 176-181.

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s ting !

Vegetable Growers Express Impressions, Concerns and Hope for Crop Biostimulants New survey helps researchers understand the current use and attitudes of biostimulants in California vegetable crops. By ZHENG WANG | UCCE Vegetable Crops Farm Advisor, Stanislaus County

rop biostimulants are many things. First, they are claimed to be multi-functional, including enhancement of soil and crop health, acceleration of soil nutrient cycling and improvement of crop productivity and fruit quality, among other benefits. Second, they are categorized by the active ingredient, application method, cost and target

Advertorial Everyone has heard the old saying, “Aglime works 1/3 each year for 3 years.” But where did this come from? The research we rely on mainly comes from the Midwest where the aglime is much more coarse. In fact, the larger particle sizes 4, 8 & 30 mesh are ineffective within 3 years. Pictured are actual aglime samples taken from Blue Mtn, CA (on the left) and Nokomis, IL. Each compartment has a mesh under it, the number indicates the size. The material above is retained on that mesh size, the material below is smaller. Particle size determines how quickly an aglime reacts, the old saying is not an accurate way to describe aglime’s efficiency.

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According to Grand View Research Inc., the global revenue generated by biostimulants was $1.74 billion in 2016, dominated by European and North American companies. Projections indicate that the market value will reach $4.14 billion by 2025. Though it is difficult to obtain an exact number of biostimulant products currently on the market, the estimate is over 600 with more becoming available each year. However,

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crops. Third, they are popular among ever-greater numbers of vegetable farmers regardless of production system, scale and commodity. Finally, some of their performance/efficacy is variable, while many others are unknown.

March / April 2021

County of California Stanislaus Kern Santa Barbara San Luis Obispo San Joaquin Fresno Monterey Imperial Yolo Sutter Merced Sacramento Madera Yuba Riverside San Bernardino San Diego Santa Cruz Santa Clara Ventura Solano

No. of grower responses 34 3 1 1 14 5 3 3 7 2 10 2 1 1 2 1 1 1 2 1 1

Table 1. List of counties for the respondents’ vegetable field locations.

this grand prosperity of crop biostimulants is not shared equally among people who use them. Particularly to vegetable growers who operate farming at every scale that differs widely in climates, production timing, marketable portion, planting techniques, field preparation and maturity, it can be extremely complex to choose the right product from the long list and use it at the right time in the right way. The first and maybe the foremost step toward a more effective use of crop biostimulants among vegetable growers is to understand their current use, experience, concerns and hopes. To accomplish the task, a survey was sent out to collect the specific information from vegetable growers mainly in the San Joaquin Valley and other counties in California.

By commodity, crops with more than 10 responses included tomato (46), pepper (23), melon (21), summer/winter squash (21), leafy greens/herbs (21), cole crops (16), watermelon (16) and onion (13). By production location, the 74 growers claimed to have their vegetable fields in 21 counties across California. For details, see Table 1.

Continued on Page 38

The Survey and Respondent

The survey was sent to approximately 648 vegetable growers in late October 2020 with the help of other UCCE advisors and commodity boards. The survey was then closed about two months thereafter before the responses were summarized. The original survey can be found at cestanislaus.ucanr.edu/ Agriculture/Vegetable_Crops/Biostimulant_Survey/. The survey contains eight questions with the first four asking growers how they farm and the last four related to their experience and opinions to crop biostimulants. By the end of December 2020, we received a total of 83 responses (12.8%), with 74 of them being valid responses (11.4%). Nine responses were not included because there were two replies without an answer to any of the question, five responses from oversea, and two responses from counties outside California. Details about the composition and production of the 74 respondents are included below and in Table 1. By production, there were 10, 27 and 37 growers claiming organic only, conventional only and mix of both. By scale, there were 31, 7 and 36 growers with vegetable production scale below 100 acres, 100 to 500 acres and over 500 acres.

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Continued from Page 37

Responses Regarding Biostimulants

The responses indicated that over half of respondents (40) know some knowledge about biostimulants, of which 37 applied biostimulants to at least one or two of their vegetable crops. There were nine growers who claimed having the highest knowledge level (very well), but two of them did not use biostimulants to any of their vegetable crops. There is no surprise that the majority of growers who responded with just a little knowledge or not knowing anything about crop biostimulants did not apply any biostimulant to any of their vegetable crops. The respondents were almost equally distributed by the application level of biostimulants (Table 2). The survey also asked the previous experience or future impression regarding the efficacy of biostimulants on improving vegetable growth. From the results, 50 growers, representing 68% of total respondents, shared the experience or impression that biostimulants could conditionally confer their efficacy. Less than 20% of the respondents indicated a consistent, positive performance on improving their vegetable crops, while only 13% gave the negative impression on biostimulant efficacy (Figure 1).

Application level of biostimulants

Understanding level of biostimulants Very well Some A little Nothing

Sub-totoal

Apply to most vegetables.

Apply to certain vegetables.

Apply to one or two vegetables.

I don’t use to any vegetables.

Sub-total

Total: 74

18 17 20

Table 2. Number of grower responses to the understanding/knowledge level of biostimulants and how much of vegetable crops growers apply biostimulants to.

Stanislaus 34 Kern I have received numerous questions in 3 impression regarding Figure 1. Responses to previous experience or future Santaefficacy. Barbara the past years from vegetable growers, 1 biostimulant their advisors and colleagues regarding Luis Obispo FigureSan 2. 1 the biostimulant selection, effect evalSan Joaquin 14 uation, quality control and incompatiFresno 5 bility with other field activities. “Going Monterey 3 in blind”, “Unable to identify the Imperial 3 benefits”, and “Snake oil” are common Yolo complaints. One of the main objectives 7 Sutter for the survey is to identify the biggest 2 concerns of using biostimulants on Merced 10 vegetable crops among growers. The Sacramento 2 survey results showed that about half of Madera 1 the respondents identified the difficulty Yuba 1 of choosing a proper product as one of Riverside 2 the main concerns followed by the risk San Bernardino of low or no return on investment. In 1 San Diego addition, concerns of incomplete label 1 Santa Cruz Figure 2. Growers’ concerns regarding the use of1 crop biostimulants on vegetable crops. Continued on Page 40 Santa Clara 2 Ventura 1 Solano 1 38 Progressive Crop Consultant March / April 2021 Concerns and Hopes

Continued from Page 38 and interference with fertilization and pesticide plans received 20 responses (Figure 2, see page 38). Lastly, the survey asked growers their agreement level to future actions of improving the use of crop biostimulants. For all future measures, an average of 89% of the respondents agreed/strongly agreed that they will be helpful and important to improve future use of crop biostimulants (Table 3). These responses reflect the hopes from growers, and their voices should be heard by academia, industry, extension and other sectors to outline future efforts aiding a practical and profitable use of these biologics.

UCCE Biostimulant Testing Trials

The UCCE farm advisors from Stanislaus County are actively working with vegetable growers and biostimulant companies to conduct various testing trials each year. The main goal is to fill the data gap with more unbiased,

Future Measures

Number of responses to each agreement level Strongly Agree

Agree

Neutral

Disagree

Strongly Disagree

Provide more instructions/ education on selecting, using, and evaluating biostimulants.

Offer more user-friendly resources aiding practical use of biostimulants.

Standardize/improve product labels and manufacturer-claimed functions.

Implement more unbiased field trials to validate the efficacy of different biostimulants.

Table 3. Number of responses to the agreement on the importance of future measures in improving the use of biostimulants.

statistically-viable product efficacy data on various vegetable commodities in the Central Valley. Since 2019, we have evaluated numerous biostimulants on processing tomato and watermelon productivity, fruit quality and plant

health. Stay tuned to our newsletter and check for previous results (Veg Views: cestanislaus.ucanr.edu/ news_102/Veg_Views/).

Helping Farmers Grow NATURALLY Since 1974 Stanislaus Kern Santa Barbara San Luis Obispo San Joaquin Fresno FEATURING: Monterey Imperial Yolo Sutter Merced Sacramento Madera Yuba Riverside San Bernardino San Diego Santa Cruz Santa Clara Ventura Solano

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References

N AV E L O R A N G E WO R M M A N AG E M E N T

Biofertilizers Market Size, Share & Trends Analysis Report By Product, By Application, And Segment Forecasts, 2012 – 2022. grandviewresearch.com/ industry-analysis/biofertilizers-industry.

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Tomato (46) and watermelon (16) each represented crops with more than 10 submitted responses (photos by Z. Wang.)

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March / April 2021

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Life After Methyl Bromide in

California Berries

Growers lean on newer fumigant alternatives to control key weed and disease pests.

BY WARREN E. CLARK, Contributing Writer

hen methyl bromide was banned in 2005, California strawberry growers lost an effective tool in their crop care toolbox to control weeds, soilborne diseases, nematodes and symphylans. Special-use permits allowed them to continue using the fumigant through 2016, but growers feared final loss of the powerful soil fumigant might be the end of profitable production.

The California Strawberry Commission agreed, noting that elimination of methyl bromide fumigation brought forth several soilborne diseases for which there is no post-plant control. Of particular concern were Fusarium wilt (Fusarium oxysporum f.sp. fragariae), Verticillium wilt (Verticillium dahlia) and charcoal rot (Macrophomina 42

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phaseolina), according to the California Strawberry Commission. But once again, necessity proved to be the “mother of invention,” said independent agronomist and PCA Lee Stoeckle, owner of Stoeckle Agricultural Consulting in Ventura, Calif. Stoeckle has advised strawberry and caneberry growers for more than 30 years, and he noted that effective alternative fumigants have taken up the methyl bromide void and are now widely and successfully used. While California strawberry acreage has fallen, total production has actually increased thanks to innovation and application of new technology. Stoeckle’s family-owned business provides recommendations on 3,000 March / April 2021

acres of strawberries and 100 acres of blackberries in Santa Barbara County and San Luis Obispo County and 2,000 acres of strawberries in Ventura County. In addition, he consults on production of 800 acres of strawberry and 250 acres of raspberries in Baja Mexico. While he is primarily responsible for above-ground insect and disease control, he doesn’t write fumigation recommendations but instead advises based on what he learns about weeds and soil pathogens.

A One-Two Punch

Top problem soilborne diseases, according to Stoeckle, are Fusarium, Macrophomina, Phytophthora, Anthracnose and Verticillium wilt. Top

Continued on Page 44

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problem above-ground pests include two-spotted spider mites, Lygus bug, Botrytis fruit rot/gray mold and powdery mildew, depending on varietal susceptibility. Other pests necessary to watch include worms and aphids. “The optimum disease and weed control program is a one-two punch,” Stoeckle says. “Hit it at the end of the season as a burndown and at the beginning before next planting via drip irrigation. The backbone of our control program is Pic-Chlor 60 EC (1,3-dichloropropene plus chloropicrin) at the max recommended rate (350 lbs/ac), going after the heavy hitting ‘big boys’ (soilborne diseases) when applied in August or September before planting.” He recommends Vapam or K-Pam to get the additional benefits to control these diseases (Fusarium, Verticillium, Macrophomina phacelia) and eliminate the inoculum reservoir in the crown.

Stoeckle says emulsified formulations of Telone® C-35 and chloropicrin can be applied with irrigation water through drip irrigation systems. Metam sodium is the active ingredient in Vapam® HL™ and metam potassium in the active ingredient in K-Pam® HL™. Both are AMVAC ® soil fumigants, which give off methyl isothiocyanate (MITC) when combined with water via drip or otherwise. If drip fumigation is planned, good results have been obtained with a sequential application of chloropicrin or 1,3-dichloropropene plus chloropicrin, followed 7 days later with metam sodium or metam potassium.

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tion is huge. We expect to see a 20% to 30% return on fumigant investment.” He is quick to add there are other management decisions that help maximize production, noting, “I could go on and on about using the best plastic mulch or optimum fertilization practices.”

Best Practice Weed Control Reduces Production Costs

Fifth-generation Santa Barbara County grower Brett Ferini, owner of Rancho Laguna Farms, grows 400 acres of strawberries (300 fall plant, 100 summer plant) and 20 acres (adding another 20 for 40 total) of blackberries. Plus, he grows 35 acres of organic blackberries. He used Vapam on blackberries in February 2020.

Stoeckle considers fumigants essential and offers the math: “If we equate the value of every plant to be $2 each and you lose 10% of your plants, that’s 2,500 “Vapam worked out really well in plants on a population of 25,000 per controlling nutgrass/nutsedge,” he said. acre. Your choice is to fumigate or take “Pic-Clor 60 has no effect.” a $5,000 loss. That’s an easy decision. The return on investment on fumigaFor weed and disease control, “we hit

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everything at fall pre-plant with PicClor 60 through drip tape and seven days after that we follow with Vapam,” he said. “It does a terrific job on nutsedge and other weeds, as well as the soilborne diseases including Verticillium, Phytophthora and, anecdotally, Macrophomina.” Ferini says the operation plans to add a Vapam burndown at the end of the 2020 growing season “We definitely [have] cut weeding by 60% on summer plant,” he says. “Labor is our highest cost. We saw $1,050 savings per acre vs. our normal costs of $1,800/acre. The big test will be on the fall plant when we get more rain. Our fall weeding cost normally runs $2,800 to $3,000 per acre. Using Pic-Clor 60 followed by Vapam treatment, I expect weeding cost savings of $1,000 to $1,500 per acre.” Also seeing results with soil fumigants

is Santa Barbara grower Josh Ford. He is COO of Ocean Breeze Ag Management LLC in Ventura, which grows 450 acres of strawberries, 50 acres of blackberries, and 25 acres of raspberries. Ford’s biggest soilborne pests are Macrophomina, Fusarium, and Phytophthora cactorum. Nutgrass is his most difficult weed to control. “We’ve been using soil fumigants for many years,” he says. “We were using methyl bromide, but now we apply chloropicrin once a year and K-Pam once to twice a season. If nut grass is a bad problem, we will knock it down at the end of the season with K-Pam and also pre-plant K-Pam. Our ROI is good when you consider the increased cost of labor to manually remove nut grass.” Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc. com

Finding the right fumigation and herbicide program can help reduce long term labor costs.

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March / April 2021

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Understanding CCA Certification Exams

By JEROME PIER, Ph.D. | CCA, PCA, Board Chairman, Western Region Certified Crop Advisors

never really understood what certification means until I heard it described by a psychometrician. I have been a Certified Crop Advisor (CCA) for nearly two decades and felt I knew what it means to be a certified professional. I recently attended the North American Certified Crop Advisors On-line Board Meeting. I listened to a presentation by Scott Thayn, Ph.D., CMS, a psychometrician, or a statistician specializing in distinguishing the differences between individuals. Thayn is the president of Certification Management Services, the third-party agency hired by the Agronomy Society to help develop and manage the testing required for certification. The presentation addressed a proposal to give rankings on how well a test taker did on the CCA exam. Board members were hearing from potential members who were unable to pass the exams and wanted more feedback to help them study for their next attempt. The proposal, and the way the statistician took it apart, were a revelation, and it got me thinking that the mechanics behind certification are not well understood.

Certification Exam Intricacies

The Home page for Certifications under the website Agronomy.org states, “Certification is the standard by which professionals are judged. The purpose of a certification program is to protect the public and the profession. It is a voluntary enhancement to a person’s career credentials. Being certified adds credibility and shows that you are serious about what you do.” A prospective candidate digging deeper would find they need to meet certain criteria to be considered a CCA: academic, experience and examination. Simply speaking, certification indicates one has demonstrated the knowledge and experience to perform at a higher level than their peers. Hearing the proposal to give test takers feedback on their performance was familiar to me as a board member who participates on the Exam Committee for the Western Region. I have heard from

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many colleagues who did not pass one or both certification exams and are frustrated by the lack of a score or indication where they underperformed. I struggled to explain to my friends why the exams were pass/fail and why they just had to keep trying. I believe the frustration lies in the expectations of an academic testing experience clashing with the reality of certification exams. Data indicates most people who take Figure 1. Distribution of ease of questions in an the certification exams are recent academic exam compared to certification testing. college graduates. Having a college degree in agriculture is a requirement for complete exam review process takes place becoming a certified crop advisor. College every four to five years. graduates have spent most of their lives with graded exams. Academic testing pres- An illustration of the difference between ents a broad range of questions to both exacademic and certification exams can be amine a student’s proficiency and encourgiven with a sports analogy. An academage them to improve. A student who gets ic exam is comparable to a high school a low grade on a test will hopefully review physical education track and field program, the questions marked incorrect and study where everyone is expected and encourthe subject to raise their grade on the final aged to participate. A certification exam, exam. This familiar approach to testing is on the other hand, is like the selection contrary to certification exams. process for the Olympic high jumping team. The high school physical education The distribution of difficulty of certificaprogram sets the bar low and gradually tion exam questions is quite narrow comraises it to help students practice their pared to an academic exam (See Figure 1). technique and jump higher. But when the The certification exam begins by defining world competition is jumping over seven competency areas, the major subjects feet, the US team would set the bar at a levthat define the everyday work of the crop el near that to select the most competitive advisor. Performance objectives rest under team. During the selection process, if the the competency areas. Each performance bar is set too high, then they don’t have a objective spawns several possible exam team, but set the bar too low and the team questions. Each exam question must be has a poor chance of winning. When the tied to a performance objective to accupsychometrician used this example, the rately test one’s comprehensive knowledge proposal to classify the specific abilities of of agronomy. test takers was withdrawn. Where an academic exam contains a large variation in question difficulty, certification exam questions ask, “What is the minimum knowledge a professional must have to be proficient in this area.” This is determined by groups of volunteer CCAs, with guidance by the Agronomy Society’s excellent statistician Dawn Gibas, Ph.D., who reviews the performance of each exam question. Questions that nearly everyone gets right are eliminated as well as those that almost no one answers correctly. A

March / April 2021

The complexity of 21st-century agriculture practiced in the Western Region of the US supports the need for the most qualified field people providing the best recommendations for our growers so we can continue to deliver the highest-quality, safest agricultural products in the world.

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