Progressive Crop Consultant - March/April 2019

March/April 2019 Redefining IPM for the 21st Century Kasugamycin for Managing Walnut Blight

How does kasugamycin-copper or -mancozeb mixtures compare to copper-mancozeb?

Moving Toward Alternatives to Chlorpyrifos for Managing Maggots in Onions The Carbohydrate Observatory: A Citizen Science Research Project

Understanding seasonal trends of starch and sugar in walnut, pistachio and almond under varying climatic conditions.

Volume 4 : Issue 2 March/April 2019

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March/April 2019

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

IN THIS ISSUE

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Redefining IPM for the 21st Century

Kasugamycin for Managing Walnut BlightHow does kasugamycincopper or -mancozeb mixtures compare to copper-mancozeb?

CONTRIBUTING WRITERS & INDUSTRY SUPPORT

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Moving Toward Alternatives to Chlorpyrifos for Managing Maggots in Onions

Carbohydrate 20 The Observatory: A Citizen Science Research Project -Understanding seasonal trends of starch and sugar in walnut, pistachio and almond under varying climatic conditions.

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Resources, University of California, Merced, CA, Department of Land, Air and Water Resources, University of California, Davis, CA, A. Dahlberg & Khaled M. Bali, Division of Agriculture and Natural Resources—Kearney Surendra K. Dara Agricultural Research CE Advisor—Entomology and Biologicals, University and Extension Center, University of California, of California Cooperative Extension, San Luis Obispo Parlier, CA, Daniele and Santa Barbara counties Zaccaria, Department of Land, Air and Water Resources, University of Anna Davidson California, Davis, CA Postdoc, Manager of the Carbohydrate Observatory Emily J. Symmes Maciej Zwieniecki, Sacramento Valley Area Professor, Founder of the Carbohydrate Observatory IPM Advisor University of California Cooperative Extension and Statewide Tapan B. Pathak IPM Program Division of Agriculture and Natural Resources, Rob Wilson University of California, UC ANR Intermountain Merced, CA, Mahesh Research and Extension L. Maskey, Division of Center Director & Farm Agriculture and Natural Advisor J. E. Adaskaveg Department of Microbiology and Plant Pathology, University of California, Riverside, CA, L. Wade, Arysta Life Science, Roseville, CA

UC COOPERATIVE EXTENSION ADVISORY BOARD

Kevin Day

Kris Tollerup

Dr. Brent Holtz

Surendra K. Dara

County Director and UCCE Integrated Pest UCCE Pomology Farm Management Advisor, Advisor, Tulare/Kings County Parlier, CA County Director and UCCE Pomology Farm Advisor, San Joaquin County

Climate Change and California Agriculture

Steven T. Koike,

Director, TriCal Diagnostics

CE Advisor—Entomology and Biologicals, University of California Cooperative Extension, San Luis Obispo

and Santa Barbara counties

Emily J. Symmes

UCCE IPM Advisor, Sacramento Valley

Many Possible 34 The Causes of “Gummy Nuts” in Almonds

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

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VI A CER

PRO

Within the group

Staying informed

Cultural

Biological

Host Plant Resistance

Behavioral

Microbial

IPM Ac�ons

Physical/ Mechanical

PEST COMMUNICATION MANAGEMENT

PLANNING & ORGANIZATION

Chemical

KNOWLEDGE & RESOURCES

Y L SAFET ETA NM RO

Among growers

EN CO NS VI UM E R

ECONO MIC AL DU

Y LIT I B

Pest

Available op�ons

Managing info

SO CIA L

Tools & Technology

R LLE SE

Monitoring

ACCEPTABILITY

Redefining IPM for the 21st Century By: Surendra K. Dara | CE Advisor—Entomology and Biologicals, University of California Cooperative Extension, San Luis Obispo and Santa Barbara counties

I

ntegrated pest management, commonly referred to as IPM, is a concept of managing pests that has been in use for several decades. The definition and interpretation of IPM vary depending on the source, such as a university, institute, or a researcher, and its application varies even more widely depending on the practitioner. Here are a few examples of its definitions and interpretations: “IPM is an ecosystem-based strategy that focuses on long-term prevention of pests or their damage through a combination of techniques such as biological control, habitat manipulation, modification of cultural practices, and use of resistant varieties. Pesticides are

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used only after monitoring indicates they are needed according to established guidelines, and treatments are made with the goal of removing only the target organism. Pest control materials are selected and applied in a manner that minimizes risks to human health, beneficial and nontarget organisms, and the environment.” UC IPM “Integrated Pest Management, or IPM, is an approach to solving pest problems by applying our knowledge about pests to prevent them from damaging crops, harming animals, infesting buildings or otherwise interfering with our livelihood or enjoyment of life. IPM means responding to pest problems with the most effective, least-

March/April 2019

risk option.” IPM Institute of North America “A well-defined Integrated Pest Management (IPM) is a program that should be based on prevention, monitoring, and control which offers the opportunity to eliminate or drastically reduce the use of pesticides, and to minimize the toxicity of and exposure to any products which are used. IPM does this by utilizing a variety of methods and techniques, including cultural, biological and structural strategies to control a multitude of pest problems.” Beyond Pesticides “IPM is rotating chemicals from

Continued on Page 6

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Continued from Page 4 different mode of action groups.” A grower These definitions and interpretations represent a variety of objectives and strategies for managing pests. IPM is not a principle that can/should be strictly and equally applied to every situation, but a philosophy that can guide the practitioner to use it as appropriate for the situation. For example, varieties that are resistant to arthropod pests and diseases are available for some crops, but not for others. Mating disruption with pheromones is widely practiced for certain lepidopteran and coleopteran pests, but not for several hemipteran pests. Biological control is more readily employed for greenhouse pests, but not to the same extent under field conditions. While chemical pesticides should be used as the last resort, in principle, sometimes they are the first line of defense to prevent damage to the transplants by certain pests or area-wide spread of certain endemic or invasive pests and diseases.

Crop production is an art, science, and business, and by adding environmental and social factors, IPM—an approach used in agriculture—can also be influenced by a number of factors.

Each grower has their own strategy for producing crops, minimizing losses, and making a profit in a manner that is acceptable to the society, safe for the consumers, and less disruptive to the environment. In other words, “IPM is an approach to manage pests in an economically viable, socially acceptable, and environmentally safe manner”.

Keeping this simple, but loaded, definition in mind and considering recent advances in crop production and protection, communication technology, and globalization of agriculture and commerce, here is the new paradigm of IPM with its management, business, and sustainability aspects.

I. Management Aspect There are four major components in the IPM model that address various pest management options, the knowledge and 6

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less suitable for the pest. Destroying crop residue and thorough cultivation will eliminate breeding sites and control soil-inhabiting stages of the pest. Crop rotation with non-host or tolerant crops will break the pest cycles and reduce their buildup year after year.

Choosing clean seed and plant material 1. Pest Management will avoid the chances of introducing pests right from the beginning of the The concept of crop production. Sanitation practices to pest control has remove infected/infested plant material, changed to pest regular cleaning of field equipment, management over avoiding accidental contamination of the years knowing healthy fields through human activity that a balanced are also important to prevent the pest approach to managing spread. Intercropping of non-host pest populations plants or those that deter pests or using to levels that do not cause economic trap crops to divert pests away from the losses is better than eliminating due to main crop are some of the other cultural environmental and economic reasons. control strategies.

Although the term control is frequently used in literature and conversations, c. Biological control: Natural enemies it generally refers to management. A such as predatory arthropods and thorough knowledge of general IPM parasitic wasps can be very effective in principles and various management causing significant reductions in pest options for all possible pest problems is populations in certain circumstances. important as some are preventive and Periodical releases of commercially others are curative. It is also essential available natural enemies or conserving to understand inherent and potential natural enemy populations by providing interactions among these management refuges or avoiding practices that options to achieve maximum control. harm them are some of the common The following are common control practices to control endemic pests. To options that can be employed at different address invasive pest issues, classical stages of crop production to prevent, biological control approach is typically reduce, or treat pest infestations. Each of employed where natural enemies from them may provide only a certain level of the native region of the invasive pest are control, but their additive effect can be imported, multiplied, and released in significant in preventing yield losses. the new habitat of the pest. The release of irradiated, sterile insects is another a. Host plant resistance: It involves the biological control technique that is use of pest resistant and tolerant cultivars successfully used against a number of developed through traditional breeding pests. or genetic engineering. These cultivars Continued on Page 8 possess physical, morphological, or biochemical characters that reduce the plant’s attractiveness or suitability for the pest to feed, develop, or reproduce Host Plant successfully. These cultivars resist or Resistance tolerate pest damage and thus reduce the yield losses.

Cultural Chemical

resources the grower has in order to address the pest issue, planning and organization of information to take appropriate actions, and maintaining good communication to acquire and disseminate knowledge about pests and their management.

IPM strategies

b. Cultural control: Modifying agronomic practices to avoid or reduce pest infestations and damage refers to cultural control. Adjusting planting dates can help escape pest occurrence or avoid most vulnerable stages of the crop to coincide with the pest occurrence. Modifying irrigation practices, fertilizer program, plant or row spacing, and other agronomic practices can create conditions that are

March/April 2019

Microbial

PEST MANAGEMENT

Mechanical/ Physical

Biological

Behavioral

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pest populations, caution should be exercised while using them.

Continued from Page 6 d. Behavioral control: Behavior of the pest can be exploited for its control through baits, traps, and mating disruption techniques. Baits containing poisonous material will attract and kill the pests when distributed in the field or placed in traps. Pests are attracted to certain colors, lights, odors of attractants or pheromones. Devices that use one or more of these can be used to attract, trap or kill pests. Pheromone lures confuse adult insects and disrupt their mating potential, and thus reduce their offspring. e. Physical or mechanical control: This approach refers to the use of a variety of physical or mechanical techniques for pest exclusion, trapping (in some cases similar to the behavioral control), removal, or destruction. Pest exclusion with netting, handpicking or vacuuming to remove pests, mechanical tools for weed control, traps for rodent pests, modifying environmental conditions such as heat or humidity in greenhouses, steam sterilization or solarization, visual or physical bird deterrents such as reflective material or sonic devices are some examples for physical or mechanical control. f. Microbial control: Using entomopathogenic bacteria, fungi, microsporidia, nematodes, and viruses, and fermentation byproducts of microbes against arthropod pests, fungi against plant parasitic nematodes, and bacterial and fungal antagonizers of plant pathogens generally come under microbial control. As repeated use of certain microbial control options can also lead to resistance development in

KNOWLEDGE & RESOURCES

Pest

Control op�ons Tools & Technology

g. Chemical control: Chemical control typically refers to the use of synthetic chemical pesticides, but to be technically accurate, it should include synthetic chemicals as well as chemicals of microbial or botanical origin. Although botanical extracts such as azadirachtin and pyrethrins, and microbe-derived toxic metabolites such as avermectin and spinosad are regarded as biologicals, they are still chemical molecules, similar to synthetic chemicals, and possess many of the human and environmental safety risks as chemical pesticides do. Chemical pesticides are categorized into different groups based on their mode of action and rotating chemicals from different groups is recommended to reduce the risk of resistance development.

Government regulations restrict the time and amount of certain chemical pesticides and help mitigate the associated risks.

The new RNAi (ribonucleic acid interference) technology where double-stranded RNA is applied to silence specific genes in the target insect is considered a biopesticide application. Certain biostimulants based on minerals, microbes, plant extracts, seaweed or algae impart induced systemic resistance to pests and diseases, but are applied as amendments without any claims for pest or disease control. These new products or technologies can fall into one or more abovementioned categories.

As required by the crop and pest situation, one or more of these control options can be used throughout the production period for effective pest management. When used effectively, non-chemical control options delay, reduce, or eliminate the use of chemical pesticides.

2. Knowledge and Resources The knowledge of various control options, pest biology and damage potential, and suitability of available resources enables the grower to make a decision appropriate for their situation. a. Pest: Identification of the pest, understanding its biology and seasonal

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March/April 2019

Ac�ons

PLANNING & ORGANIZATION

Managing Info Monitoring

population trends, damaging life stages and their habitats, nature of damage and its economic significance, vulnerability of each life for one or more control options, host preference and alternate hosts, and all the related information is critical for identifying an effective control strategy. b. Available control options: Since not all control options can be used against every pest, the grower has to choose the ones that are ideal for the situation. For example, systemic insecticides are more effective against pests that mine or bore into the plant tissue. Pests that follow a particular seasonal pattern can be controlled by adjusting planting dates.

Commercially available natural enemies can be released against some, while mating disruption works well against others. Entomopathogenic nematodes can be used against certain soil pests, bacteria and viruses against pests with chewing mouthparts such as lepidoptera and coleopteran, and fungi against sucking pests. c. Tools and technology: A particular pest can be controlled by certain options, but they may not all be available in a particular place, for a particular crop, or within the available financial means. For example, the release of natural enemies may be possible in high-value specialty crops, but not in large acreage field crops. A particular pesticide might be registered against a pest on some crops, but not on all. Use of netting or tractor-mounted vacuums can be effective, but very expensive limiting their availability to those who can afford.

This is a critical component where diagnostic and preventive or curative decisions are made based on available and affordable control options.

3. Planning and Organization This component deals with the management aspect of the new IPM model for data collection, organization, and actual actions against pest infestations. a. Pest monitoring: Regularly monitoring the fields for pest occurrence and spread is a basic step in crop protection. Early detection in many cases can help address the pest situation by low-cost spot treatment or removal of pests or infected/ infested plant material. When pest infestations continue to grow, regular monitoring is necessary to assess the damage and determine the time to initiate farm-wide control.

Monitoring is also important to avoid calendar-based pesticide applications especially at lower pest populations that do not warrant treatments.

actions are taken at the right time. Good farm management will allow the grower to take timely actions. These actions are not only necessary to prevent damage on a particular farm, but also to prevent the spread to neighboring farms.

When pest management is neglected, it leads to area-wide problems with larger regulatory, social, and economic implications.

4. Communication Good communication to transfer

the individual or collective knowledge for the benefit of everyone is the last component of the new IPM model. Modern and traditional communication tools can be used for outreach as university and private researchers develop information about endemic and invasive pests, emerging threats, and new control strategies.

Continued on Page 10

b. Managing information: A good recordkeeping about pests, their damage, effective treatments, seasonal fluctuations, interactions with environmental factors, irrigation practices, plant nutrition, and all related information from year to year will build the institutional knowledge and prepares the grower to take preventive or curative actions. c. Corrective actions: Taking timely action is probably the most important aspect of IPM. Even with all the knowledge about the pest and availability of resources for its effective management, losses can be prevented only when corrective

Within the group

Staying upto-date

Within the community

COMMUNICATION

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Continued from Page 9 a. Staying informed: Growers and pest control professionals should stay informed about existing and emerging pests and their management options.

Science-based information can be obtained by attending extension meetings, webinars, or workshops, reading newsletter, trade, extension, or scientific journal articles, and keeping in touch with researchers and other professionals through various communication channels. Wellinformed growers can be well prepared to address pest issues. b. Communication within the group: Educating farm crew through periodical training or communication will help with all aspects of pest management, proper pesticide handling, ensuring worker safety, and preventing environmental contamination. A knowledgeable field crew will be beneficial for effective implementation of pest management strategies. c. Communication among growers: Although certain crop production and protection strategies are considered proprietary information, pests do not have boundaries and can spread to multiple fields when they are not effectively managed throughout the region. Sharing knowledge and resources with each other will improve pest control efficacy and benefit the entire grower community.

In addition to these four components with an IPM model, factors that influence profitable, safe, and affordable food production at a larger scale and their implications for global food security should also be included. There are two layers surrounding these four components addressing the business and sustainable aspects of food production.

II. Business Aspect Consumers want nutritious, healthy, and tasty produce that is free of pest damage at affordable prices. Growers try to meet this demand by producing food that meets all the consumer needs, while maintaining environmental and 10

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human safety and still being able to make a profit. Sellers evaluate the market demand and strategize their sales to satisfy consumers while making their own profit to stay in the business. In an ideal system, consumer, producer, and seller would maintain a harmonious balance of food production and sale. In such a system, food is safe and affordable to everyone, there will be food security all over the world, and both growers and sellers make a good profit with no or minimal risk to the environment in the process of food production.

However, this balance is frequently disrupted due to 1) consumers’ misunderstanding of various food production systems, their demand for perfectly shaped fruits and vegetables at affordable prices or their willingness to pay a premium price for food items that are perceived to be safe, 2) growers trying to find economical ways of producing high quality food while facing with continuous pest problems and other challenges, and 3) sellers trying to market organic food at a higher price as a safer alternative to conventionally produced food. If growers implement good IPM strategies to produce safe food and consumers are aware of this practice and gain confidence in food produced in an IPM system, then sellers would be able to market what informed-consumers demand.

III. Sustainability Aspect As mentioned earlier, IPM is an approach to ensure economic viability at both consumer and producer level (seller is always expected to make a profit), environmental safety through a balanced use of all available pest control options, and social acceptability as food is safe and affordable.

While organic food production is generally perceived as safe and sustainable, the following examples can explain why it is not necessarily true. Organic food production is not pesticide-free and some of the pesticides used in an organic system are as harmful to humans

March/April 2019

and non-target organisms as some chemical pesticides. Certain organically accepted pesticides have toxins or natural chemical molecules that are very similar to those in synthetic pesticides.

In fact, some synthetic pesticides are manufactured imitating the pesticidal molecules of natural origin. Mechanical pest control practices such as vacuuming or tilling utilize fossil fuels and indirectly have a negative impact on the environment. For example, diesel-powered tractors are operated for vacuuming western tarnished bug in strawberry 2-3 times or more each week compared to a pesticide application typically requires the use of tractor once every 7-14 days. To control certain pests, multiple applications of organic pesticides might be necessary with associated costs and risks, while similar pest populations could be controlled by fewer chemical pesticide applications. It is very difficult to manage certain plant diseases and arthropod pests through non-chemical means and inadequate control not only leads to crop losses, but can result in their spread to larger areas making their control even more difficult. Many growers prefer a good IPM-based production to an organic production for the ease of operation and profitability. However, they continue to produce organic food to stay in business.

While middle and upper-class consumers may be willing to pay higher prices for organically produced food, many of the low-income groups in developed and underdeveloped countries cannot afford such food.

Organic food production can lead to social inequality and a false sense of wellbeing for those that can afford it.

Food security for the growing world population is necessary through optimizing input costs, minimizing wastage, grower adoption of safe and sustainable practices, and consumer confidence in food produced through such practices. IPM addresses all the economic, environmental, and social aspects and provides safe and affordable food to the consumers and profits to producers and sellers, while maintaining environmental health.

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

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Kasugamycin for Managing Walnut Blight

How do kasugamycin-copper or -mancozeb mixtures compare to copper-mancozeb?

By: J. E. Adaskaveg | Department of Microbiology and Plant Pathology, University of California, Riverside, CA, L. Wade | Arysta Life Science, Roseville, CA

Figure 1. Pistillate flowers developing into healthy walnut fruitlets (left) and showing a primary infection (center) at the blossom end.

Developing walnuts (right) with primary (blossom end) and secondary (fruitside) infections. All photos courtesy of Jim Adaskaveg.

K

asugamycin (tradename Kasumin) was registered in 2018 for managing walnut blight and bacterial canker and blast on sweet cherry. The bactericide was already federally registered for fire blight on pome fruit, but in 2018, registration for this disease was also approved in California.

Kasugamycin is a unique bactericide because it is not used in animal or human medicine. Environmental monitoring studies have shown that it does not select for human bacterial pathogen resistance with uses in plant agriculture.

Furthermore, kasugamycin has its own Fungicide Resistance Action Committee (FRAC) Code 24 or mode of action that is different from other registered plant agricultural bactericides like streptomycin (FRAC Code 25) and oxytetracycline (FRAC Code 41). Kasugamycin meets new toxicology standards for pollinating insects (e.g., honey bees), it has a low animal toxicity with a “Caution” rating and a 12 h re-entry time on the label. As with any cautionary pesticide, mixers and applicators need to have standard personal protective equipment (PPE) when handling the bactericide.

Copper is classified as FRAC Code M1 for the first element historically used for fungal and bacterial disease control.

Copper affects many physiological pathways in plant pathogens and is classified as having a multi-site (M) mode of action. Not many bactericides have been developed for managing plant bacterial diseases, and fewer have been registered. Thus, there has been a great dependency on copper. Because of the multi-site classification, many

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agriculturalists thought that plant pathogens would not develop resistance to copper. Unfortunately, after many years of usage, bacterial pathogens such as the walnut blight pathogen, Xanthomonas arboricola pv. juglandis (Xaj), have developed resistance to copper. This is a direct result and lack of alternative bactericides available of overuse of one active ingredient (i.e., copper) and being limited with the lack of bactericides available to apply modern approaches to resistance management such as rotating between active ingredients with different modes of action and limiting the total number of applications of any one mode of action per season as part of following “RULES” (http://ipm.ucanr.edu/PDF/ PMG/fungicideefficacytiming.pdf).

Over-usage of any one active ingredient, such as copper, can create other environmental issues only including soil contamination, orchard water-runoff, higher concentrations in watersheds, and potential crop and non-crop phytotoxicity especially in perennial crop systems.

After the industry used copper exclusively for approximately 50 years (1930s to 1980s), copper-maneb (e.g., Manex) mixtures were first identified for use on walnut in 1992 and emergency registrations ensued for 22 years before a full registration was obtained for the related compound mancozeb in 2014. The walnut industry and University of California (UC) researchers knew that more alternatives were needed, otherwise someday the pathogen would develop resistance

March/April 2019

to copper-mancozeb. Because copper resistance had already developed, this selection pressure is maintained and resistance levels are increasing even when mancozeb is used in the mixture, because copper has been the only tank mix option. In effect, resistance management is not being effectively practiced since copper-resistance already exists and the use of mancozeb (M3) is selecting for resistant strains of the bacterial pathogen to the mancozeb mode of action. In the presence of copper resistance, having only one treatment (i.e., mancozeb) available to manage a disease not only can limit crop production each season but could economically devastate the entire industry by making harvests sporadic and inconsistent, lowering crop quality, and preventing profitability. Growers and the entire walnut industry consider walnut blight a threat to the industry and their livelihood.

Why do we need kasugamycin for managing walnut blight? There is a great need to develop other modes of action for managing bacterial diseases including walnut blight that can be integrated into management programs.

Kasugamycin was identified, developed, and registered for the purpose of resistance management, reducing over-usage of any one mode of action, and sustaining the walnut industry of California. The aminoglycoside bactericide has a unique mode of action (FRAC Code 24) as stated above and can be used in combination with copper or mancozeb. When kasugamycin is used in combination with mancozeb,

resistance management is being practiced since resistance has not been found in Xaj pathogen populations to either mode of action.

Use on Walnuts Kasugamycin is labeled as Kasumin for managing walnut blight at 64 fl oz/A in a minimum of 100 gal water/A for ground application. The full 64 fl oz per acre labeled rate for kasugamycin should always be used.

Adjuvants that are stickers may also be used, whereas spreaders and penetrants should be avoided. Reduced spray volumes may be utilized for small trees provided that the volume of water is sufficient to provide good coverage of treated foliage. Applications should be initiated when conditions favor disease development. This is the same timing as for copper-mancozeb. In orchards with a history of the disease and when high rainfall is forecasted, applications should be initiated at 20-40 percent catkin expansion. Under less favorable conditions for disease (i.e., low rainfall forecasts and minimal dews), applications should start at 20-40 percent pistillate flower expansion (also known as the “prayer stage”). The preharvest interval is 100 days or approximately mid- to late June depending on the walnut cultivar harvest date. The minimal re-application interval is seven days. The current labeled use of Kasumin allows for two applications or 128 fl oz of product per season with a label change for up to four (256 fl oz) per season planned later this year. Still, only two consecutive applications will be allowed without rotating to other modes of action. Alternate row applications, applications in orchards that are being fertilized with animal waste/manure, or animal grazing in orchards treated with Kasumin are not allowed. The first restriction is to prevent selection of resistant isolates of the target pathogen, Xaj; whereas, the latter two restrictions are to ensure that the selection of non-target, human-pathogen bacteria is prevented.

For walnut blight management, the best way to use the bactericide is in combination with mancozeb or copper. Application management strategies for a four- or fivespray mixture, rotation program include, but are not limited to, the following: A) Copper/mancozeb—kasugamycin/ mancozeb—kasugamycin/copper—copper/ mancozeb B) Copper/mancozeb—kasugamycin/ mancozeb—copper/mancozeb— kasugamycin/copper— copper/mancozeb

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Continued from Page 13 How do kasugamycin treatments compare to coppermancozeb treatments in managing disease? The research used to develop kasugamycin was based on a 7- to 10-day re-application interval. The reason for this was that Kasumin is only locally systemic or translaminar and thus, is less likely to be re-distributed. With new growth increasing the canopy volume weekly in the spring as walnut trees come out of dormancy, multiple and frequent applications are necessary.

Kasugamycin-mancozeb mixtures applied in our research trials were often the most effective of all treatments evaluated.

In general, bactericides have a short residual life of a few days to a week or two. In toxicology in-vitro testing, Xaj is only moderately sensitive to kasugamycin with a mid-range to high minimum inhibitory concentration (MIC) value.

When kasugamycin is mixed with mancozeb, the MIC of the mixture is approximately 5 parts per million (ppm).

Radial streaks of 16 isolates of Xaj on each plate exposed to different toxicants. Top image: Copper 50 ppm (fixed concentration). Spiral gradient plates with highest concentration towrds the center and lowest concentration at the edge of the plate. Middle image: Kasugamycin (gradient range 0.5 to 64.9 ppm); and Bottom image: Kasugamycin + mancozeb (concentration gradients).

Lack of growth towards the center of each plate indicates inhibition. No inhibition for copper at 50 ppm whereas inhibition concentrations averaged 20 and 5 ppm for kasugamycin and the kasugamycinmancozeb mixture, respectively.

Figure 2. Radial streaks of 16 isolates of Xaj on each plate exposed to different toxicants. Right image: Copper 50 ppm (fixed concentration). Spiral gradient plates with highest concentration towards the center and lowest concentration at the edge of the plate. Middle image: Kasugamycin (gradient range 0.5 to 64.9 ppm); and Left image: Kasugamycin+mancozeb (concentration gradients). Lack of growth towards the center of each plate indicates inhibition. No inhibition for copper at 50 ppm whereas inhibition concentrations averaged 20 and 5 ppm for kasugamycin and the kasugamycinmancozeb mixture, respectively.

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Kasugamycin is applied at 64 fl oz per 100 gal or 100 ppm. Thus, the labeled rate is kasugamycin-mancozeb mixtures are approximately 20X of the MIC value for Xaj. Because of the short residual activity and a moderate buffering residue (20X), the rotation needs of bactericide mixtures containing kasugamycin described above need to be applied in 7to 10-day intervals (Figure 3).

Kasugamycin and Resistance Resistance is a relative term indicating a change in sensitivity to an inhibitory compound. A moderately high MIC for a bactericide does not mean that the pathogen is resistant. We have conducted baseline studies with kasugamycin, kasugamycin-copper, and kasugamycinmancozeb for Xaj with MIC values of 20, 8.3, 5.3 ppm, respectively (Figure 2, see page 14). This was done before the bactericide was registered in California to determine any change in sensitivity after registration and commercial usage.

To date, resistance has not been found and isolates evaluated are all within the baseline distributions. Still, with a single site mode of action compound such as kasugamycin, there is a risk for selecting resistant sub-populations of the pathogen especially when resistance management strategies are not employed.

This is the reason why we developed the mixture-rotation programs suggested above.

Conclusions The integration of bactericides with different modes of action and application strategies of rotations of mixtures of bactericides with different modes of action with forecasting tools such as XanthoCast (http://www.agtelemetry. com/) should provide the stewardship necessary for having the tools available for managing walnut blight for years to come. The hope with the Kasumin registration is to provide resistance management and prevent or reduce the risk of resistance to copper-mancozeb while new approaches can be developed and integrated to protect all of these compounds. Walnut blight is the most serious disease impacting growers in California and multiple tools like kasugamycin, copper, and mancozeb need to be available to maintain a successful industry.

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

Treatment (Rate of ai oz/A) Control

a

ATD - 12.9

b

Kasugamycin - 1.3

bc

Kasugamycin + ATD - 1.3 + 12.9

bc

Copper + Mancozeb - 24 + 28.4

bc cd

Kasugamycin +Copper - 1.3 + 24 Kasugamycin + Mancozeb - 1.3 + 28.4 d Copper - 24 d

2

0

4

6

8

10

Disease incidence (%)

Figure 3. Efficacy of treatments for managing walnut blight.

Treatments applied using an air-blast sprayer (100 gal/A). The walnut blight pathogen was sensitive to copper.

Disease incidence is the number of diseased nuts per 100 nuts evaluated. ATD = amino thiadiazole, an experimental bactericide. Bars followed by the same letter are not significantly different.

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15

Yellow sticky traps work well for determining the number of seed corn maggot flies and onion maggot flies in onion fields.

All photos courtesy of Rob Wilson.

Moving Toward Alternatives to Chlorpyrifos for Managing Maggots in Onions

By: Rob Wilson | UC ANR Intermountain Research and Extension Center Director & Farm Advisor

C

hlorpyrifos, an organophosphate pesticide used to kill of number of insect pests, has been the go-to insecticide for managing maggots in California onions. For many years, chlorpyrifos applied in-furrow at planting provided effective control of maggots in fresh market and dehy onions.

Unfortunately, serious environmental concerns associated with chlorpyrifos and the potential for insecticide resistance is forcing the onion industry to find alternative insecticides. Starting on January 1, 2019, the California Department of Pesticide Regulation (DPR) has recommended County Agricultural Commissioners implement interim re-

strictions on chlorpyrifos use. Detailed information on the interim restrictions and regulations can be found on the DPR website at https://www.cdpr. ca.gov/docs/pressrls/2018/111518.htm.

DPR is completing a formal regulatory process to list chlorpyrifos as a toxic air contaminant with permanent restrictions, but until the regulatory process is complete, interim restrictions are in place.

Onion and Seed Corn Maggot Both onion maggot, Delia antiqua, and seed corn maggot, Delia platura, are problem pests in California onions.

Differences in onion stand caused by maggot feeding for various insecticide treatments in IREC research plots. The plot with few onions is the untreated control.

16

Progressive Crop Consultant

March/April 2019

Larvae of both species feed on young onion plants, often resulting in seedling mortality and onion stand reduction by more than 50 percent of desired seeding rate. Seed corn maggot flies lay their eggs in fields in spring and larvae live in the soil and feed on seeds and developing plants of several crops. Onion maggot flies lay their eggs in young onion fields and larvae live in the soil feeding on onions belowground. Onion maggots are specific to onions and other allium crops. Preventative farming practices such as late plantings, increasing seeding rates, avoiding tilling manures and crop residues shortly before planting, and removing onion culls can prevent damage from maggots, but preventative measures alone are not always effective, especially in fields with heavy maggot pressure.

Insecticide applied at planting provides the most consistent control of maggots. The key to effective insecticide use for maggot control is applying the insecticide prophylactically at the time of planting. Growers shouldn’t wait to apply insecticides until maggot larvae are found as maggot larvae feed on seeds, germinating plants, and young onions. This feeding results in rapid plant mortality, thus insecticide application after planting is rarely effective.

Research Research studies at the University of California (UC) UC Intermountain

Continued on Page 18

March/April 2019

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17

Continued from Page 16 Research and Extension Center (IREC) in Tulelake, California are investigating insecticides and insecticide application methods to find alternatives to chlorpyrifos. This research effort has received admirable support from the California Garlic and Onion Research Advisory Board with the hopes of pro-actively finding alternatives before chlorpyrifos restrictions. Insecticide applications at planting can be made in-furrow, broadcast, or as a seed treatment. IREC research has shown the efficacy of different application methods is dependent on insecticide choice. For example, spinosad was only effective when applied as a seed treatment (Regard) as spinosad (Entrust) applied in-furrow at planting had similar onion stands compared to the untreated control.

resulted in the highest onion stands in a field with a combination of maggots and smut. In fields without smut, thiram and FarMore F300 fungicide package gave good early season disease control in IREC studies.

Yellow sticky traps placed along field edges can offer growers an early warning for potential maggot problems (see picture). Seed corn maggot and onion maggot flies are readily captured on sticky traps and the traps (changed once a week) provide growers an indication of the number of flies during onion establishment. Tillage of green plants, plant residues, and manures attract thousands of egg-laying female flies and crop damage is often severe when crops are planted within the first

Insecticide Alternatives to Chlorpyrifos Seed treatment with spinosad (FarMore OI100 and FI500) or clothianidin (Sepresto) provided similar or better suppression of maggot compared to chlorpyrifos at the maximum labeled rate in-furrow. This trend was true multiple years in multiple studies conducted at IREC. Outside the research world, multiple Tulelake onion growers had success using spinosad or clothianidin seed treatments instead of chlorpyrifos in 2017 and 2018.

Applying chlorpyrifos in combination with spinosad and clothianidin seed treatment did not increase onion stands compared to using either seed treatment alone. Cyromazine (Trigard) seed treatment is another alternative. Trigard provided similar maggot suppression compared to FarMore FI500 and Sepresto in 2018, and it is seed treatment used in other parts of the United States for maggot control. Bifenthrin was the only tested insecticide applied in-furrow that provided similar efficacy compared to chlorpyrifos. Unfortunately, bifenthrin is not currently labeled for use in California onions.

few weeks of tillage. Cool, wet weather and delayed plant emergence are other factors that promote crop damage from seed corn maggot. First generation maggots are most problematic as their feeding kills seedling plants, but later generation maggots can feed on plants and bulbs in the summer. Damage from later generation onion maggot is rarely economically important in California except for fields with diseased, decaying onion bulbs making mid-season and late season disease control important to prevent late season maggot problems.

Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com Hand-harvesting onions to determine yield differences.

Early season onion stand differences caused by maggot feeding.

Other Considerations Fungicides used in combination with insecticide seed treatment may influence onion stands. In 2018, Sepresto (insecticide) + FarMore F300 (fungicide) + pro-gro (fungicide) 18

Progressive Crop Consultant

Late season onion maggot feeding on an onion bulb.

Seed corn maggot larvae feeding on onion seedling.

March/April 2019

March/April 2019

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19

The Carbohydrate Observatory: A Citizen Science Research Project

Redding

Salt Lake City

Provo

Reno

Understanding seasonal trends of starch and sugar in walnut, pistachio and almond under varying climatic conditions.

Yuba City

Sacramento Santa Rosa Napa Petaluma

Vallejo

Antioch

San Francisco

By: Anna Davidson | Postdoc, Manager of the Carbohydrate Observatory and Maciej Zwieniecki | Professor, Founder of the Carbohydrate Observatory

Stockton Tracy

Hayward

San Jose

St. George

Santa Cruz Watsonville

Fresno

Salinas Monterey Soledad

Topo

Las Vegas

Satellite Paso Robles

Streets

San Luis Obispo

rsfield

Almond Orchards

Kingman

Walnut Orchards

Santa Maria

Pistachio Orchards

Lancaster

Lompoc Santa Barbara

Palmdale

Pecan Orchards

Victorville Lake Havasu

Figure 1. Map of the California Central Valley with all participating almond (red), pistachio (green) and walnut (blue) orchards.

O

Background

ne can consider that the currency of nut trees are non-structural carbohydrates (NSCs), meaning sugar and starch. Carbohydrates provide the energy for growth, defense, and healthy flowering, ultimately resulting in yield. Soluble carbohydrates or sugar, can be considered as the cash that flows around the tree assuring growth and paying for services like defense from pests, frost, or mineral uptake. Starch is the form of currency that can be considered as the savings account, which is stored in the wood and roots of the tree during dormancy to be used in the following spring. Seasonal trends of sugars and starches are highly dynamic and can fluctuate with species, variety, tree age, temperature, climate, and management practices.

The physiological changes in terms of carbohydrate dynamics a tree undergoes in preparation for dormancy especially in warmer climates, is still poorly understood. This is especially true due to the negative effects resulting

20 Progressive Crop Consultant

from climate variability including the decrease in winter fog, chilling hours, winter drought, and an increase in annual temperatures. To better understand the seasonal fluctuations of carbohydrates, we decided to take an accelerated approach to do research in trees. Instead of having a single study with few variables, we use the entire Central Valley as our research laboratory. To accomplish such a task, we take a citizen scientist approach with the help from growers, farm advisors, and commodity boards. From ~450 sites around the state, walnut, almond, and pistachio growers send us monthly samples of twigs and bark based on a very simple and fast protocol. Monthly samples allow us to track the seasonal trends over several years so that we may make well-informed decisions on the timing and nature of our management practices.

Protocol Growers simply clip one twig from three representative trees, about four inches at the base of the current season’s

March/April 2019

growth, remove the bark and drop the three sticks and bark in an envelope and mail it to us with information including the name of the site, date, species and variety, orchard age, and latitude and longitude. Once the samples reach us through the mail, we dry them, grind them, weigh them, and perform a chemical analysis in the laboratory to determine the amount of sugar and starch of each sample. We then upload all results to our web-based interactive map (Figure 1) (https:// mzwienie.shinyapps.io/Shiny_test/) and data analysis tool (https://zlab-carbobservatory.herokuapp.com/) where growers can access their data in real time and follow their own trends of starch and sugar in each orchard they sample. One can also compare multiple orchards at a time. All analyses are free of charge to participants.

Results Figure 2 (see page 22) shows the 2016/17 seasonal trends of carbohydrates in in walnuts, almonds and pistachios. Higher levels of

Continued on Page 22

March/April 2019

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21

Carbohydrate recovery

300

2017 pre dormancy level

2017 boom 2016 winter level 200 NSC_wood

species almond pistachio walnut

100

Figure 2. Seasonal patterns of soluble sugars and starch concentration in three major tree crop species walnut, almond and pistachio during the 2016-2017 seasons. Each data point represents a single orchard. Lines are running average content of the total carbohydrate concentration in wood.

0 300

400

Julian_Day

500

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Bark

Concentration [mg/g DW]

300

NSCs Starch

Twig

2016

2017

2016

2017

200

150

100

50

2016

0 1.0

2017 Soluble carbohydrates Starch

0.8

Relative Content

Figure 3. Season dynamics and relative content of soluble sugars and starch in wood, bark, and total in walnut twigs. Despite high variation in total content ration between sugars and starch remains relatively constant throughout the year.

600

0.6

0.4

0.2

0.0

2016 2017 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct

2016 2017

2016 2017

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct

Continued from Page 20 carbohydrate in the winters of 2016 and 2017 provide the carbohydrates or energy to support spring bloom.

During summer, all species reduced reserves to low levels reflecting a demand for carbohydrates to support yield and tree growth that exceeds or is equal to photosynthetic supply. In the fall, carbohydrate levels recover and accumulate reserves going into dormancy and ultimately for the following spring. Interestingly, walnut shows symptoms of very late recovery underlying the need for the postharvest management even in October.

Pistachio (green) accumulated almost 22 Progressive Crop Consultant

twice as much carbohydrate in the fall of 2017 compared to 2016 potentially reflecting its strong alternating crop behavior—2016 was considered an OFF year, 2017 was an ON year, and 2018 was an OFF year, potentially supported by an increased accumulation of NSCs. We also found that from preliminary analyses of data from the Carbohydrate Observatory that starch to soluble sugars ratio is relatively constant during a year (Figure 3).

The citizen science approach allows us to look across multiple variables like

March/April 2019

climate, tree age, rootstock, yield, etc.

Initial looks at the accumulation of starch and sugar versus tree age revealed that older trees tend to accumulate much higher levels of carbohydrates in twigs potentially reflecting their reduced relative growth in relation to leaf biomass and increase of yield potential (tree investment in reproduction). This information also allows for assessing the goal of carbohydrate accumulation during post-harvest management while preparing trees for dormancy within each age group.

Continued on Page 24

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March/April 2019

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23

Wood

Bark

Total

300

Figure 4. Relationship between tree age (planting time) and 2017 carbohydrate content in twigs during winter months and during summer. Winter content of NSCs was much higher in older trees then in young trees however this difference was not as pronounced during summer.

dormant tree summer

NSCs concentration

250

200

150

100

50

6

5

01 >2

-2 11 20

-2

01

01

0

5 06

-2

00 20

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-2

<1

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11 20

-2

00 01 20

06

-2

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-2

-2

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-2

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-2 95 19

<1

99

0

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0

Year of planting

Our newest data analysis tool (http:// zlab-carb-observatory.herokuapp.com; Figure 5) allows anyone to compare different orchards of any of the three nut species with any combination of differences. For example, Figure 5 compares two different walnut orchards, one old dry farmed-dying orchard (in green) located in Paso Robles and one young organic irrigated orchard in Winters. The old dry farm has no reserves in the summer and is using everything it possibly can to survive. It likely puts little effort into making new vegetative growth.

Conclusions In the future, we hope to look further into how starch and sugar content relate to variety, climate variations, yield, and management practices. We need more data and more participation by growers to find the answers to these questions.

Please consider joining our long-term study!

Carbohydrates [mg/g DW]

Continued from Page 22 400

All farms Old Dry Farmed Walnuts

350

Young Irrigated Walnuts

300

200 150 100 50 0 Jul 2016

Interested in Participating?

Please contact Anna Davidson by email adavidson@ucdavis.edu or by phone (815) 212-4409.

Please go to our website to access more information, our protocol, map and data analysis tools. http://www.plantsciences.ucdavis.edu/ plantsciences_faculty/zwieniecki/CR/ cr.html Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com 24 Progressive Crop Consultant

Figure 5. Comparison of two different walnut orchards, one old dying orchard (in green) located in Paso Robles and one young organic irrigated orchard in Winters.

250

March/April 2019

Jan 2017

Jul 2017

Jan 2018

Date

Jul 2018

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March/April 2019 at www.progressivecrop.com 25 Contact Joseph Witzke: 209.720.8040 or Visit us online www.wrtag.com

Climate Change and California Agriculture

By: Tapan B. Pathak | Division of Agriculture and Natural Resources, University of California, Merced, CA, Mahesh L. Maskey, Jeffery A. Dahlberg, Khaled M. Bali, Daniele Zaccaria | University of California, Division of Agriculture and Natural Resources (UCANR), Faith Kearns | Division of Agriculture and Natural Resources California Institute for Water Resources, University of California, Oakland, CA

C

Climate change trends in California

Introduction

alifornia is the largest and most diverse agricultural state that produces over a third of the country's vegetables and two-thirds of fruits and nuts. Among 400 different commodities, California is a leading producer of many of those commodities [1]. At the same time, changing climate signals such as temperatures, precipitation patterns, extreme calamities and water availability poses many challenges to the state’s agricultural sector, which would not only translate into national food security issues but also economic impacts that could disrupt state and national commodities systems.

Recent publication by Pathak et al.

[2] outlined a detailed literature review to document the most current understanding on California´s climate trends in terms of temperature, precipitation, snowpack, and extreme events such as heat waves, drought, and flooding, and their relative impacts on the state’s highly productive and diverse agricultural sector. For instance, both average and extreme temperatures and precipitation patterns influence crop yields, pest, and the length of the growing season. Because of climate change, extreme events, such as heat waves, floods, and droughts, may lead to larger production losses, earlier spring arrival, and warmer winters due to temperature increases allow disease and pest pressure increase, shrinking snowpack leading to a greater risk for agriculture water availability.

This paper summarizes key findings from that paper in the context of: (a) historic trends and projected changes in temperature, precipitation and heat waves; (b) current situation and future expectations of drought and flood; and (c) consequent impacts on agriculture.

26 Progressive Crop Consultant

The climate of California varies from hot desert to subarctic environments lying in the proximity to the Pacific Coast with Mediterranean climate influenced by the cold ocean currents and offshore winds. This section reviews historical and projected trends of key climatic parameters: temperature, precipitation, and extreme events like heat waves, drought and floods.

Temperature Climate change in California is often exemplified by increased temperature in both space and time. While temperature has globally increased by 1.4°F since

1880, the rate of increase in minimum temperature is greater than that of mean or maximum temperatures.

Figure 1 shows that observed mean temperature in the state has been increasing from 1.3 to 2.3 °F in the past century [3]. The recent severe drought in the state has been exaggerated by increased temperature and insignificant precipitation. As seen in Table 1 (see page 27), summer after spring happens with the largest warming trends and least warming is experienced during winter and spring after implying inter-annual variability for the period from 1895 to 2018 [4]. However, least warming during fall and winter has been reported for the period 1895-2010.

Spatial variation of temperature also reveals that Southern part of the state

Degrees (F)

2.0

0.0

-2.0

1900

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

2010

Figure 1: California statewide mean temperature departure in (°F), October through September [3]. Black line denotes 11-year running mean.

March/April 2019

experiences greater warming than compared to Northern California.

Outcome of different climate models reveals that there will be more pronounced increment in summer temperature than in winter resulting into more warming in inland areas than in coastal regions. The increasing temperature trends will decrease the snow-to-precipitation ratio [5]. The state’s Sierra snowpack starts to melt earlier and faster than usual due to frequent heat spells [6]. For instance, future trends for far north and far south of the state are presented in Figure 2 (see page 28) which suggests how temperatures will continue to increase until 2100 under different emission scenarios from different climate models. Precipitation is a crucial parameter to state’s water supply for the agricultural purposes and such parameter exhibits significant inter-annual variability [3]. The variability of precipitation in California is a unique phenomenon implying that such unpredictability is more notable in California than

Table 1: California temperature departures, 1895-2018, for mean, max and min linear trends in °C within the period shown [4].

Linear departures A. Mean Temperature 1895-2018 1949-2018 1975-2018 B. Max temperature 1895-2018 1949-2018 1975-2018 C. Min temperature 1895-2018 1949-2018 1975-2018

Annual

Winter

Spring

Summer

Fall

+1.88 +2.03 +1.32

+1.55 +4.74 +2.12

+1.20 +0.46 +0.89

+3.07 +2.02

+1.70 +0.89 +0.68

+1.58 +1.18 +0.79

+1.68 +4.74 +2.39

+0.80 +0.29 +2.39

+2.82 +0.86 +0.75

+1.02 +0.59 +0.04

+2.18 +2.87 +1.85

+1.42 +4.74 +1.85

+1.60 +1.21 +1.72

+3.31 +3.18 +2.43

+2.39 +2.36 +1.40

+1.59

other parts of the country. Having Mediterranean climate, most of the rainfall happens during cool season (October to April). Despite having unnoticeable temporal pattern, study shows total annual precipitation has increased at an average rate of 5 millimeter (mm) per decade for the contiguous 48 states. In addition, there is increase in extreme single day precipitation events and increased temporal Continued on Page 28

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27

Maximum Temperature ( F)

instance, future trends for far north and far south of the state are presented in Figure 2 which suggests how temperatures will continue to increase until 2100 under different emission scenarios from different climate models.

94 92 90 88 86 84 82 80 78 76 74 72

86 84 82 80 78 76 74 72

1960 1980 2000 2020 2040 2060 2080

Maximum Temperature ( F)

1960 1980 2000 2020 2040 2060 2080 94 92 90 88 86 84 82 80 78 76 74 72

86 84 82 80 78 76 74 72

1960 1980 2000 2020 2040 2060 2080

1960 1980 2000 2020 2040 2060 2080

Figure 2: California historical and projected maximum temperature for the period 1950-2099 for Shasta (top), and Los Angeles County (bottom). Left: projection based on RCP4.5 and Right: RCP8.5 [7]. These annual values from four climate models: HadGEM2-ES (red), CNRM-CM5 (cyan), CanESM2 (dark yellow) and MIROC5 (magenta).

Year 1900 1925 1950 1975 2000 2018 1664 parameter 1693 North Coast 2168 supply for 1925 1509 purposes1427 Precipitation is a crucial to state’s water the agricultural and such parameter significant inter-annual variability variability1156 of precipitation 1114 1525 [3]. The 1294 912in North Central exhibits1132 California implying that such notable in California 492 478 655 unpredictability 519 is more 493 491 Northeastis a unique phenomenon than other parts of the country. Having Mediterranean climate, most of the rainfall happens during 1049 956 1667 1140 958 1159 Sierra cool season (October to April). Despite having unnoticeable temporal pattern, study shows total 438 420 626 448 459 567 Sacramento-Delta annual precipitation has increased at an average rate of 5 millimeter (mm) per decade for the 531 522 750 526 549 753 Central Coast contiguous 48 states. In addition, there is with increase in extreme single day precipitation events San Joaquin Valley 293 256 296 246 282 354 and increased temporal precipitation variability as observed in Table 2.

South Coast 333 290 246 293 297 376 Table 2: California annual year) precipitation starting from 345 1900 South Interior 383 (calendar376 271 every 25 years 345 except 2018383 in mm in 11 climatological regions [4] 127 158 95 101 Mohave Desert 129 116 61 115 38 53 95 51 Sonoran Desert Year Region Name

3.2. Precipitation

Region Name

1900

1925

1950

1975

2000

2018

North Coast

1664

1693

2168

1925

1509

1427

North Central

1132

1114

1525

1294

1156

912

Northeast

492

478

655

519

491

493

Sierra Continued from Page 27

1049

956

438

420

Sacramento-Delta

precipitation variability as observed in Table 2.

Projections depicted from global climate model surmise that the nature of state’s precipitation will probably change with more intense atmospheric rivers and longer dry spells between them. The simulations from general circulation models (GCM) suggest that California will maintain its Mediterranean climate with relatively cool and wet winters and hot dry summers. As expected, insignificant linear trends at a 95 percent confidence 28 Progressive Crop Consultant

Figure 2: California historical and projected maximum temperature for the period 1950-2099 for Shasta (top), and Los Angeles County (bottom).

Left: projection based on RCP4.5 and Right: RCP8.5 [7]. These annual values are from four climate models: HadGEM2-ES (red), CNRM-CM5 (cyan), CanESM2 (dark yellow) and MIROC5 (magenta).

interval1667 is observed1140 in Figure 31159 (see page 29) implying that that variability 626 448 567 of annual precipitation will continue during the next century and that the state will be vulnerable to both drought and flood.

Extreme Heat Waves California is expected to have increased intensity and frequency of heat waves.

As an illustration, Figure 4 (see page 30) shows how heat events are increasing and will continue under different emission scenarios for Kern County [7]. As seen, the number of such events will be increased more in

March/April 2019

Table 2: California annual (calendar year) precipitation every 25 years except 2018 starting from 1900 in mm in 11 climatological regions [4].

magnitude under RCP 8.5 than under 958

RCP 4.5. Several studies show that if the night temperature sustained above normal, the plants keeps metabolizing starch as photosynthetic sugars may be used in the rapid plant growth, consequently resulting into reduced dry matter. Such may cause considerable damage to crop and yields depending on whether heat waves occur during the critical crop growth stage [8].

459

Drought and Flood The effect of ongoing drought is not only limited to agricultural crop production but also risk of wild fires

Mediterranean climate with relatively cool and wet winters and hot dry summers. As expected, insignificant linear trends at a 95 percent confidence interval is observed in Figure 3 implying that that variability of annual precipitation will continue during the next century and that the state will Figure 3: Historical and projected precipitation trend for the Sacramento. Left: projection based on RCP4.5 and Right: RCP8.5 [7]. These annual be vulnerable both HadGEM2-ES drought and flood. values from four climate to models: (red), CNRM-CM5 (cyan), CanESM2 (dark yellow) and MIROC5 (magenta).

Emissions continue to rise strongly through 2050 and plateau around 2100(RCP 8.5) Modeled Data (2006-2099)

Emissions peak around 2040, then decline (RCP 4.5)

50 45 40 35 30 25 20 15 10 5

Range of annual average values from all 32 LOCA downscaled climate models HadGEM2-ES Modeled Variability Envelope CNRM-CM5 CanESM2 Observed Data (1950-2005) MIROC5

Precipitation (inches/year)

Precipitation (inches/year)

Range of annual average values from all 32 Modeled Data (2006-2099) LOCA downscaled climate models HadGEM2-ES Modeled Variability Envelope CNRM-CM5 CanESM2 Observed Data (1950-2005) MIROC5

1960 1980 2000 2020 2040 2060 2080

55 50 45 40 35 30 25 20 15 10 5

1960 1980 2000 2020 2040 2060 2080

Figure 3: Historical and projected precipitation for flooding the Sacramento. based on spring streamflow that dries out vegetation due to declining ground water trend more eventsLeft: andprojection further influence levels. DecisionRCP4.5 makers are aware of such measure in theHadGEM2-ES Sacramento River and Right: RCP8.5 [7]. These annual values[10]. fromFor fourinstance, climate models: (red), basin experience referring popular drought index called the Palmer earlier peak runoff time after last 40 decades of last century[11] CNRM-CM5 (cyan), CanESM2 (dark yellow) and MIROC5 (magenta).

Drought Severity Index (PDSI) [9]. The historical reducing the ability to refill reservoirs after the flood season is variability of the PDSI tells the state’s most severe over and indicating a flood-drought pattern within the state Extreme HeatusWaves drought conditions that happened during the 2013-14 which may potentially invite frequent flood events in California. is expected of heat As an how the monthly winter over the last California 122 years of record. to have increased intensity Figure 5 and andfrequency Table 3 (see pagewaves.

31) illustrate stream flow peaks willcontinue be shiftedunder by the end of the century for and will different illustration, Figure 4 shows how heat events are increasing Warmer environments possibly both[7]. winter emission also scenarios for increase Kern County As seen, the number of such events will be increased more in Continued on Page 30 flooding and summer water deficits and there will be

magnitude under RCP 8.5 than under RCP 4.5. Several studies show that if the night temperature sustained above normal, the plants keeps metabolizing starch as photosynthetic sugars may be used in the rapid plant growth, consequently resulting into reduced dry matter. Such may cause considerable damage to crop and yields depending on whether heat waves occur during the critical crop growth stage [8].

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can swing, depending on the type of stress and adaptation measures implemented.

Continued from Page 29 American River. As observed, while the peak happened in the month of May over the last 90 years, such will be shifted as earlier as January.

Many fruit and nut crops require cold temperatures in winter to break dormancy, which defines a location’s suitability for the production of many tree crops. These fruit and nut species adapted to temperate or cool subtropical climates where chilling each winter is needed to achieve homogeneous and simultaneous flowering and steady crop yields. The lack of adequate chilling hours as projected by climate change can delay pollination and foliation that reduces fruit yield and quality. Climate change may have impact on the incidence and severity of plant pests and disease and influence the further coevolution of plants and their pathogens. Moreover, plant diseases could be used as indicators of climate change in which the environment can move from disease-suppressive to disease-conducive or vice versa.

Key impact on California Agriculture Global crop production needs to be double by 2050 to meet the projected demand for food from rising population, diet shifts, and increasing biofuels consumption [12].

Increased temperature due to climate change can intensify this challenge. As defined in Table 4 (see page 31), individual crops have specific optimum temperature ranges for optimum production and exposure to extremely high temperatures during these growth stages can affect growth and yield.

Figure 6 (see page 32) reveals the impacts of climate change on crop yields for different field crops such as alfalfa, cotton, maize, winter wheat, tomato, rice, and sunflower in Yolo County and throughout the Central Valley assessed through a process-based crop model [14-15]. Alfalfa yields were predicted to increase under climate change, while yields from tomato and rice remain unaffected. Overall, 4°C increase in temperature may reduce yields from most fruits by more than 5 percent, which may reach up to 40 percent in some important regions [16]. However, these modeling projections did not take into account technological trends, water stress, and other management practices. Therefore, the yield numbers

Conclusions and Future Recommendations A range of studies on trends and impacts of climate change on California agriculture presented in this paper justifies

Continued on Page 32 Warm Days

55 50 45 40 35 30 25 20 15 10 5 0 80 70 60 50 40 30 20 10 0

80 70 60 50 40 30 20 10 0

1960

1980

2000

2020

2040

Historical (1950-2005)

Future (2006-2099)

Observed historical and modeled historical data

Modeled future projections

1980

2000

2020 Year

1960

1980

2000

2040

2020

2040

Historical (1950-2005)

Future (2006-2099)

Observed historical and modeled historical data

Modeled future projections

1980

2000

2020 Year

2040

CNRM-CM5 (Cooler/Wetter)

Warm Nights

< Historical (1950-2005) Future (2006-2099) >

1960

1960

Observed (1950-2005) HadGEM2-ES (Warm/Drier)

Warm Days

55 50 45 40 35 30 25 20 15 10 5 0

< Historical (1950-2005) Future (2006-2099) >

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2080

2060

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2060

CanESM2 (Average)

55 < Historical (195 50 45 40 35 30 25 20 15 10 5 0 2080 2100 1960 1980 100 90 Historical 80 Observed modeled h 70 60 50 40 30 20 10 0 8 2080 5 of 2100 1960 1980 MIROC5 (Complement)

Observed (1950-2005)

HadGEM2-ES

Future (2006-2099) > 55 < Historical Figure (1950-2005) 4: Historical and projected Heat days and Warm nights for K 50 based on RCP4.5 and Bottom: RCP8.5 [7].

45 40 35 30 Drought and Flood 25 20 15 The effect of ongoing drought is not only limited to agricultu 10 5 wild fires that dries out vegetation due to declining ground water 0 2100 1960 1980 2000 2020 2040 2060 2080 2100 of such measure referring popular drought index called the Palm 100 90 The historical variability of the PDSI tells us the state’s most s [9].

Historical (1950-2005) Future (2006-2099) 80 Observed historical and Modeled future projections modeled historical data happened during the 2013-14 winter over the last 122 years of rec 70 60 50 Warmer environments also possibly increase both winter flo 40 30 and there will be more flooding events and further influence spri 20 10 Sacramento River basin experience earlier peak runoff time af the 0 reducing ability the flood season i 2100 [11]1960 1980 the 2000 2020to refill 2040 reservoirs 2060 2080after 2100 Year

flood-drought pattern within the state which may potentially inv California.

5 andHeat Table 3 illustrate how the monthly stream Figure 4: HistoricalFigure and projected days and Warm nights for Kern Figure 4: Historical and projected Heat days and Warm nights for Kern County.

Top:and projection County.

Top: projection based onAmerican RCP4.5 Bottom:As RCP8.5 [7]. end of the century for River. observed, while the pe based on RCP4.5 and Bottom: RCP8.5 [7]. over the last 90 year, such will be shifted as earlier as January.

Observed (1950-2005) HadGEM2-ES (Warm/Drier)

30 Progressive Crop Consultant

CNRM-CM5 (Cooler/Wetter)

CanESM2 (Average)

MIROC5 (Complement)

Observed (1950-2005)

March/April 2019

HadGEM2-ES (Warm/Drier)

CNRM-CM5 (Cooler/Wetter)

CanESM2 (Average)

MIROC5 (Complement)

Observed HadGEM2-ES (Warmer/Drier) CNRM-CM5 (Cooler/Wetter) CanESM2 (Average) CanESM2 (Average)

Drought and Flood

9,000

10,000

he last 122 years of record. over the last 90 year, such will be shifted as earlier as January. crease both winter flooding and summer water deficits Observed HadGEM2-ES (Warmer/Drier) CNRM-CM5 (Cooler/Wetter) CanESM2 (Average) CanESM2 (Average) further influence spring streamflow [10]. For instance, in 9,000 10,000 Observed Data er peak runoff time after last 40 decades of last century 9,000 8,000 1922-2014 8,000 7,000 season is over and indicating a Model Projections fter the flood 7,000 1950-2099 6,000 6,000 h may potentially invite frequent flood events in 5,000 5,000 4,000 ow the monthly stream flow peaks will be shifted by the 4,000 3,000 3,000 bserved,2,000 while the peak happened in the month of May 2,000 ELIMINATES FOOD SOURCES THAT CAN CAUSE: 1,000 earlier as1,000 January.

ORGANIC TREE WASH

er/Wetter)

Oct Nov

Dec Jan

Feb Mar Apr May Month

Jun

Jul

Aug

Sep

Oct Nov Dec Jan • Fire Blight

Mar Apr May •Feb Canker Month

Ju

10,000 Figure 5: Historical and projected monthly stream flow (cubic •feet per second) American Riv Gummosis • Botfor Diseases ved Data Observed Data 9,000 014 1922-2014 8,000 Fair Oaks. Left: projection based on RCP4.5 and Right: RCP8.5 [7].

Projections Model Projections 7,000 099 1950-2099 ENHANCES FRUIT COLOR 6,000 5,000 Table 3: Magnitude of monthly stream flow (cubic feet per second) at midpoint of the hydrograp 4,000 shown in Figure 5 [7] Use for, Tree Nuts, Stone 3,000 2,000 Fruits, Apples, Pears, Citrus, Emission Scenario Observed HadGEM2-ES CNRM-CM5Avocados, CanESM2 MIRO 1,000 Aug

Sep

Oct Nov RCP 4.5

Dec Jan

Sep

36,031

Figure 5: Historical and projected monthly stream flow (cubic feet per second) for American River at Fair Oaks. Left: projection based on RCP4.5 and Right: RCP8.5 [7].

29,274

RCP 8.5

Feb Mar Apr May 21,635 Month

21,635

Jun

Jul 26,613

Aug

27,290

stream flow (cubic feet per second) for American River at and Right: RCP8.5 [7].

Emission Scenario RCP 4.5 RCP 8.5

Observed 21,635 21,635

HadGEM2-ES CNRM-CM5 26,613 36,031 27,290 29,274

CanESM2 33,496 36,665

w (cubic feet per second) at midpoint of the hydrographs

MIROC5 25,794 25,556

CNRM-CM5

CanESM2

36,031

33,496

Climatic 29,274 Classification

Hot

Warm

Cool-Warm

Cool

Crop

Acceptable Temperature for 36,665 Germination ( C) O

Watermelon Melon Sweet potato Cucumber Pepper Sweet corn Snap beans Tomato Onion Garlic Turnip Pea Potato Lettuce Cabbage Broccoli Spinach

21-35 21-32 16-35 16-35 16-35 16-30 16-30 10-30 7-25 10-35 10-30 7-26 5-26 10-30 10-30 4-16

MIROC5 25,794

Optimal Temperature 25,556 for yield( C)

Acceptable Temperature Growth Range ( C)

25-27

18-35

O

25,794

ALSO HELPS TO CONTROL 36,665GROUND SQUIRRELS, GOPHERS, MICE, AND VOLES.

Begin Spraying at bud break or 2 to 4 inch shoot growth, two quarts per 100 GPA.

Table 3: Magnitude of monthly stream flow (cubic feet per second) at midpoint of the hydrographs shown in Figure 5 [7].

EM2-ES

and Blueberries.

33,496

Repeat every 14 days, mixes well with fertilizers, we recommend using,

PURE PROTEIN DRY 15-1-1

O

20-25

12-30(35)

20-25

7-30

18-25

5-25

16-25

5-25(30)

16-18(25)

5-25

Table 4: Temperature thresholds for selected vegetable crops [13].

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25,556

Reduced chill, increased pest pressures, increased water demand and waterinduced stress, as well as variable and unreliable water supply are examples of factors that are projected to adversely impacting yield and quality of various crops grown in California. Such impacts may further intensify the challenges to meet the local and global food demands.

For this reason, there is urgent need to address such issues with resource limitations and food security challenges.

There is a clear need for localized agricultural adaptation research that could alleviate agricultural risks due to increased temperatures and extreme heat. Water being a central issue for California, there needs to be a priority on agricultural adaptation to water shortages. To help growers manage risks, it is important to develop locally relevant, need-based decision support tools that can effectively integrate various stressors to help growers make informed choices. Research only has value if it leads to informed decisionmaking, so stakeholder engagement should be the central component of climate and agricultural research.

References 1.CDFA (California Department of Food and Agriculture). California Agricultural Statistics Review 2015-2016. Available online: https://www.cdfa.ca.gov/statistics/ PDFs/2016Report.pdf (accessed on 16 June 2017).

2.Pathak, T.; Maskey, M.; Dahlberg, J.; Kearns, F.; Bali, K.; Zaccaria, D. Climate change trends and impacts on California agriculture: a detailed review.

Agronomy, 2018, 8(3), 25.

3.DWR (California Department of Water Resources). Hydroclimate Report. Water Year 2017.

4.California Climate Tracker. Generate Products Available online: https://wrcc. dri.edu/Climate/Tracker-/CA/ (accessed on 19 January 2019) 5.DWR (California Department of Water Resources). California Climate Science and Data for Water Resources 32 Progressive Crop Consultant

10 0 -10 -20 -30

Alfalfa 2020

Percent Change

Continued from Page 30 the importance of enhancing adaptive capacity of agriculture to reduce vulnerability to climate change and gain substantial benefits. The observed changes in climate added and will continue to add increasing pressure on agricultural production systems in California.

Safflower 2040

2060

2080

2100

2020

2040

Maize 2060

2080

2100

2020

2040

2060

2080

2100

2060

2080

2100

10 0 -10 -20 -30

Tomato 2020

2040

Rice 2060

2080

2100

2020

Wheat 2040

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2100

2020

2040

10 A2 Higher Emissions Scenario

0

B1 Lower Emissions Scenario

-10 -20 -30

Cotton 2020

2040

Sunflower 2060

2080

2100

2020

2040

2060

2080

2100

Figure 6: Crop Yield response to warming Year in California’s Central Valley [14].

Management. Available online: http://www.water.ca.gov/climatechange/ docs/CA_-Climate_Science_and_Data_ Final_Release_June_2015. pdf (accessed on 19 June 2017).

6.Reid, C.E.; O’Neill, M.S.; Gronlund, C.J.; Brines, S.J.; Brown, D.G.; DiezRoux, A.V.; Schwartz, J. Mapping community determinants of heat vulnerability. Environ. Health Perspect, 2009, 117, 1730–1736.

7.Cal-adapt. Exploring California’s Climate Change Research. Available online: http://cal-adapt.org/tools/ annual-averages/#climatevar-=tasm ax&scenario=rcp45&lat=38.59375&l ng=-121.

8.Wreford, A.; Adger, W.N. Adaptation in agriculture: historic effects of heat waves and droughts on UK agriculture.

International Journal of Agricultural Sustainability, 2010, 8(4), 278-289.

9.Zargar, A.; Sadiq, R.; Naser, B.; Khan, F.I. A review of drought indices.

Environmental Reviews, 2011, 19, 333349.

10.Sommer, L. With Climate Change, California Is Likely To See More Extreme Flooding.

Available online: http://www.npr. org/2017/02/28/517495739/withclimate-change-california-is-likelyto-see-mo-re-extreme-f looding, 2017 (accessed on 19 June 2017).

11.DWR (California Department of Water Resources). California Climate Science and Data for Water Resources Management. Available online: http:// www.water.ca.gov/climatechange/docs/ CA_-Climate_Science_and_Data_ Final_Release_June_2015. pdf

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12.Ray, D.K.; Mueller, N.D.; West, P.C.; Foley, J.A. Yield trends are insufficient to double crop production by 2050. PLoS One, 2013, 8, 1-7.

13.Hatfield, J.; Boote. K.; Fay, P.; Hahn, L.; Izaurralde, C.; Kimball, B.A.; Mader, T.; Morgan, J.; Ort, D.; Polley, W.; Thomson, A.; Wolfe, D; Agriculture, In: The effects of climate change on agriculture, land resources, water resources, and biodiversity. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research, Washington DC., USA, pp 21-74, 2008 14.Lee, J.; De Gryze, S; Six, J. Effect of climate change on field crop production in California’s Central Valley. Climatic Change, 2011, 109(1), 335-353.

15.Jackson, L.E.; Wheeler, S.M.; Hollander, A.D.; O’Geen, A.T.; Orlove, B.S.; Six, J.; Sumner, D.A.; Santos-Martin, F.; Kramer, J.B.; Horwath, W.R.; Howitt, R.E.; Tomich, T.P. Case study on potential agricultural responses to climate change in a California landscape, Climatic Change, 2011, 109(1), S407-S427.

16.Zilberman, D.; Kaplan, S. Giannini Foundation of Agricultural Economics, University of California.

An Overview of California’s Agricultural Adaptation to Climate Change. Available online: https://s. giannini.ucop.edu/uploads/giannini_ public/73/c8/73c82d70-b296-442482f6-2c04c7859aa4/-v18n1 _6.pdf (accessed on 26 June 2017).

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

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The Many Possible Causes of “Gummy Nuts” in Almonds

Photo 1. Anthracnose infection symptoms on almond hull. Photos courteys of B. Holtz, University of California Cooperative Extension.

By: Emily J. Symmes | Sacramento Valley Area IPM Advisor University of California Cooperative Extension and Statewide IPM Program

B

eginning in March, there are a number of biological factors and non-biological conditions that may cause “gumming” in almonds.

When we refer to “gummy nuts”, we are actually referring to a suite of different symptoms depending on which part of the fruit is affected. To distinguish those in this article, the term “hull gummosis” refers to the exudates (typically clear to amber in color) that are visible on the outside of the fruit. Depending on the cause and extent of fruit damage, we may also observe gumming evident on the shell and in the kernel, in addition to other symptoms.

In order to develop the best approach to maintaining crop health and kernel quality, it is important to be able to distinguish among the various causes of hull, shell, and kernel gumming.

In general, dissection of the fruit, as well as a holistic approach to assessing the orchard is necessary to determine the cause of symptom expression and potential for significant crop damage.

Often, once hull gummosis and possible underlying kernel damage are observed, the window of opportunity or ideal treatment timing to prevent or mitigate the cause of already-damaged fruit has passed. However, understanding how to best identify the cause of symptoms, relationships to other orchard factors that lead to the development of symptoms and damage, and the

34 Progressive Crop Consultant

timing of initial onset will allow you to develop improved monitoring and crop protection strategies.

Diseases With most hull gummosis arising from disease infection, there will typically be other signs and disease symptoms apparent on other parts of the plant.

Additional factors such as orchard history of disease, timing of symptom development, cultivars affected, and weather patterns conducive to particular disease development can help distinguish the cause(s) of symptoms being observed in the orchard. The most common pathogen-induced infections that can lead to hull gummosis include anthracnose and bacterial spot.

Anthracnose When small nuts are infected, they shrivel and turn a rusty orange color.

When larger nuts are infected, they exhibit round, sunken, orangish lesions and profuse hull gummosis as the infection progresses into the kernel.

Anthracnose gummosis is typically amber in color with multiple exudate sites on the hull (Photo 1). Eventually, infected nuts die and remain attached to the spur as mummies.

Other signs and symptoms of anthracnose infection may be evident

March/April 2019

on flowers, foliage, spurs, shoots, limbs, and branches. Blossom blight of infected flowers looks similar to brown rot strikes. Infected leaves tend to develop water-soaked lesions that eventually fade in color, developing into marginal necrosis. Leaves die but often remain attached to branches. Dieback often occurs on shoots and branches that bear infected nuts.

Prolonged warm (>59°F), rainy weather, especially extending well into spring, are most conducive to disease spread and development. Summer infections can occur if irrigation contacts the tree canopy. All varieties are susceptible, with Butte, Fritz, Monterey, Peerless, Price, and Winters among the most susceptible, and Nonpareil considered less susceptible to anthracnose infection. Symptom development on the outside of the fruit (i.e., hull gummosis) is dependent on the timing of initial infection and rate of disease progression. In most years, it is evident by mid- to late-April.

Bacterial Spot The most obvious symptoms of infection occur on nuts. Typically, hull lesions begin as small water-soaked circular spots. Infections enlarge and become necrotic, with obvious lesions

Continued on Page 36

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Photo 2A. Necrotic lesions under almond hull caused by bacterial spot infection.

Continued from Page 34

Continued from Page 34 developing inward into the hull, shell, and kernel (Photo 2A). Infection sites on the hull exhibit profuse amber colored gumming, often from multiple exudate sites (Photo 2B). Early-season infections can cause fruit drop.

margin of the leaf, eventually becoming chlorotic then necrotic, leaving irregular shaped holes (Photo 2C). If the disease is severe, defoliation can occur. Twig lesions may develop on green shoots.

Leaf and shoot symptoms may occur, but are less common than fruit symptoms. Small, water-soaked, circular leaf lesions develop along the midrib and toward the tip and

High moisture conditions and warm temperatures (> 68°F) favor infection.

Severe infections are most common with frequent periods of rainfall or irrigation during fruit development.

Fritz is highly susceptible to bacterial spot infection and symptom development. Other varieties such as Butte, Carmel, Monterey, Nonpareil, Padre, and Price are also susceptible but generally exhibit less disease severity. Hull gummosis symptoms are first visible one to three weeks after initial infection, therefore appearance will be related to when the favorable conditions for infection occurred that season. In most years, bacterial spot hull gummosis symptoms become apparent by mid- to lateApril.

Insects

Photo 2B. Bacterial spot infection symptoms on almond hull.

A number of insects of different types can cause hull gummosis. We 36 Progressive Crop Consultant

March/April 2019

Photo 2C. Foliar symptoms of bacterial spot infection.

tend to most commonly associate its appearance with Hemipteran insects, or “true bugs” (i.e., those with piercingsucking mouthparts), particularly leaffooted bugs and stink bugs. In addition to these, a number of other “bugs” may be present in orchards and cause some extent of hull gummosis (e.g., box elder bugs, Phytocoris species, Calocoris species) but often without significant kernel or crop damage.

Entries by Lepidopteran (worm) pests may also result in hull gummosis (i.e., peach twig borer and oriental fruit moth). What follows focuses on distinguishing leaffooted and stink bug feeding in almond.

Hull gummosis expression and the extent of shell and kernel damage caused by bug feeding differs depending upon the insect species and life stage (adults or nymphs), the growth size and

Continued on Page 38

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varieties are more susceptible to kernel damage for a longer period during the season.

LFB damage typically occurs in a fairly distinct window of time, usually during March and April. Hull gummosis caused by LFB usually manifests 3 to 10 days after the initial feeding occurrence.

As season progresses into May and June, the LFB feeding decreases while stink bug feeding by species commonly encountered in almond orchards can increase. Monitor for visual evidence of LFB adults, nymphs, and egg masses (Photo 3) from March to early May. Basing treatments on the appearance of significant hull gummosis or aborted nuts on the ground may be ineffective, as there can be more than a one-week lag time between feeding and evidence of symptoms, and dispersing insects may have moved out of the orchard by that time.

Photo 3. Leaffooted bug egg mass on almond. Photo courtesy of Integral Ag, Inc.

Continued from Page 36 stage of the fruit being fed on (therefore, seasonal timing of damage), and the variety. The key factors for differential fruit symptom expression involve the length of the insect mouthpart and what part of the fruit tissue it can reach (differs based on species, and among adults and nymphs of a species); hull thickness and shell hardness (which both vary in time and among varieties); and stage of kernel development when the feeding occurred. In addition, feeding wounds caused by bugs can provide openings for secondary pathogens to invade the fruit (e.g., bacteria, yeast, fungi) and some plantfeeding bugs are known to inject salivary enzymes which may exacerbate damage symptoms.

insects themselves (adults, nymphs, or egg masses), but other factors such as timing, extent of damage, and landscape characteristics can assist in the evaluation.

In general, when evaluating insectcaused hull gummosis, shell, and kernel damage, darkened feeding channels are evident upon dissection into the hull, and may extend into the shell and kernel (based on the factors noted above). The most accurate way to distinguish which bug species are causing the damage is by visual observation of the presence of the

Hull gummosis caused by LFB feeding is clear to light-yellow, originating from each feeding site. Therefore, there can be single or multiple hull gummosis sites, but we often observe multiple exudates on individual nuts arising from LFB infestation. The extent of kernel damage depends on if the feeding entry made it through the shell and into the kernel. Softer shell almond

38 Progressive Crop Consultant

Leaffooted Bugs (Family Coreidae) Leaffooted bug (LFB) feeding on young fruit prior to shell hardening can cause the kernel to wither and abort, and may lead to nut drop. LFB feeding impacts lessen as the season progresses, with kernel damage decreasing as shells harden. After shells begin to harden, feeding may still cause dark spots and gumming of the kernel, or wrinkled and misshaped kernels.

March/April 2019

Stink Bugs (Family Pentatomidae) There are a number of species of stink bugs that can be found in almond orchards. These include green stink bug (most commonly encountered), redshouldered stink bug, Uhler stink bug, and rough stink bug. Be aware that rough stink bugs are not plant pests; they are predators of other insects.

More recently, the invasive brown marmorated stink bug (BMSB) has been reported in a few almond orchards in the northern San Joaquin Valley. BMSB will be addressed in a separate section in this article.

Feeding by the more common stink bugs in almond orchards typically occurs from May through July.

Movement into orchards in spring occurs when other hosts (weeds, other plants, crops) dry down, so this can be earlier in years with dry winters/ springs. The appearance of hull gummosis is similar to LFB (clear to light-colored gumming, often exuding from multiple puncture holes), but the timing of incidence is a key factor in separating the two. Because stink bug feeding occurs later in the season than LFB feeding, it typically only extends into the hull, and nut abortion and kernel damage are rare. However, severe feeding may impact quality

Continued on Page 40

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Continued from Page 38 due to misshapen or wrinkled kernels, perhaps due to increases in secondary pathogens. Stink bugs are generally less mobile than LFB, so feeding tends to be more localized (clustered) in the orchard. Additionally, monitoring or observing visual evidence of stink bug adults (Photo 4), nymphs, and barrelshaped egg masses, can help indicate whether they were the likely cause of fruit symptoms.

Brown Marmorated Stink Bug BMSB has been present in California since 2008, but has only recently begun to move into some agricultural commodities (commercial kiwifruit detection beginning in 2014, peach in 2016, and almond in 2017). Because this is an invasive species with a very wide host range, minimal natural controls, and highly aggregative behavior, there is considerable concern as to the potential impacts should it become more widespread and established in California agricultural crops.

To date in almond, reports of serious infestation and damage have been limited to a few orchards in Stanislaus and Merced counties, but it is important to be aware of how to determine the possible presence of this pest in almond orchards, and how to distinguish damage caused by BMSB versus other bug feeding. Evidence of feeding (hull gummosis from multiple feeding sites) and shell and kernel damage by BMSB seems to be similar to LFB (if occurring earlier in the season, before shell hardening) or other stink bugs (if occurring later in the season, after shell hardening), although the severity may appear greater for BMSB due to its aggregative nature (infest in larger numbers in clustered areas of orchards).

Recent research by University of California Cooperative Extension (UCCE) Area IPM Advisor Jhalendra Rijal in the impacted orchards indicates that BMSB may move into almonds and begin feeding as early as mid-

March, and may continue well into summer. Therefore, it may be difficult to distinguish whether hull gummosis, nut drop, and/or kernel damage observed in March and April was caused by LFB or BMSB feeding. If hull gummosis is occurring later in the summer, it may be difficult to distinguish between BSMB or other stink bugs.

Researchers are actively working on traps and lures for LFB, but to date, none are commercially available.

Fortunately, there are traps and lures available for BMSB. In addition to trapping and visual observations of the pests themselves (adults, nymphs, egg masses), taking into account landscape-scale characteristics and location of the damage in the orchard may help indicate the source of damage if occurring during the same time period as either LFB or other stink bugs.

For BMSB, pay particular attention to border rows next to overwintering

Continued on Page 42

Photo 4. Adult green stink bug on almond. Photo courtesy of Integral Ag, Inc.

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Continued from Page 40 aggregation shelters (e.g., structures, wood piles), other known hosts (e.g., tree of heaven is known to harbor high populations of BMSB), and riparian/ natural environment interfaces.

Other Causes of Hull Gummosis A number of other factors may result in the expression of hull gummosis. These include physical causes (such as hail or tractor strikes to the fruit), nutrient deficiency (i.e., boron), herbicide damage, and physiological responses.

Boron deficiency will typically manifest as clear gummosis on the sides of the hull or at the suture line. Copious internal gumming and discoloration the of developing kernel will be visible upon dissection (Photo 5). Fruit drop may occur, or, if nuts remain in the tree, internal gumming will harden and cause misshapen kernels. Boron status can be evaluated by analyzing hull samples.

Physiological processes, not relating to any of the aforementioned sources,

may result in hull gummosis. This is thought to be due to rapid expansion of the growing kernel, causing increased pressure on the shell and hull. Dissection of the fruit will show a water-soaked gummy area on the outside of the shell, clear gummosis exuding from the suture line or side of hull, and no apparent feeding channel (that would indicate bug as the culprit).

Kernels appear healthy and affected nuts often remain on the tree with no negative impacts.

In summary, hull gummosis in almonds can be caused by a number of different biological and non-biological factors.

Appearance of hull gummosis may be indicative of more severe crop damage if kernels are also impacted, but this is not always the case. Understanding how to best identify the sources of such symptoms is a key component for effective integrated pest management and crop production programs.

More detail on identification and management of all of the potential causes of hull gummosis, shell, and kernel gumming damage can be found

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on the UC Statewide IPM Program online Pest management Guidelines for Almonds (ipm.ucanr.edu/PMG/ selectnewpest.almonds.html), and in multiple posts at the Sacramento Valley Orchard Source Website (http://www. sacvalleyorcards.com/) and the Almond Doctor Blog (http://thealmonddoctor. com/).

Photo 5. Symptoms of boron deficiency in almond kernel. Photo courtesy of D. Lightle, University of California Cooperative Extension.

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