Progressive Crop Consultant - November/December 2018

November/December 2018 Optimizing Root Lesion Nematode Management In Red Raspberry Post Harvest Irrigation Management for Vineyards Tomato Powdery Mildew: Managing the Disease to Minimize Impacts and Avoid Fungicide Resistance Safe, Profitable, and Practical Label for Sustainable Production and Food Security

WALNUT TRADE SHOW

January 4, 2019 See page 15 for details

PUBLICATION

Volume 3 : Issue 6 Photo courtesy of Lisa DeVetter

November/December 2018

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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 4

Optimizing Root Lesion Nematode Management in Red Raspberry

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Post Harvest Irrigation Management for Vineyards

CONTRIBUTING WRITERS & INDUSTRY SUPPORT Brenna Aegerter UCCE Farm Advisor for San Joaquin County Mark Bolda UC Cooperative Extension, Santa Cruz County Surendra K. Dara CE Advisor—Entomology and Biologicals, University of California Cooperative Extension, San Luis Obispo and Santa Barbara Counties

Kris Tollerup University of California Cooperative Extension Area-wide IPM Advisor, Kearney Agricultural Tom Walters Walters Ag Research Inga Zasada USDA-ARS

Lisa DeVetter Washington State University

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Tomato Powdery Mildew: Managing the Disease to Minimize Impacts and Avoid Fungicide Resistance.

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Safe, Profitable, and Practical Label for Sustainable Production and Food Security

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Spotted Wing Drosophila in Caneberries: A Ten Year Retrospective

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Put Leaffooted Bug Monitoring on Your Winter and Spring To-Do List

UC Cooperative Extension Advisory Board Kevin Day

County Director and UCCE Pomology Farm Advisor, Tulare/Kings County

Dr. Brent Holtz

County Director and UCCE Pomology Farm Advisor, San Joaquin County

Emily J. Symmes

UCCE IPM Advisor, Sacramento Valley

Kris Tollerup

UCCE Integrated Pest Management Advisor, Parlier, CA

Steven T. Koike,

Director, TriCal Diagnostics

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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Optimizing Root Lesion Nematode Management in Red Raspberry

By: Lisa DeVetter | Washington State University, Tom Walters | Walter Ag Research, and Inga Zasada | USDA-ARS Photo courtesy of Lisa DeVetter

W

ashington State leads national production of processed red raspberry with a single county (Whatcom) responsible for 97 percent of in-state production. Growers in Whatcom County produced just over 68 million pounds of fruit in 2017 with raspberry production contributing to the vibrancy of the rural economy in northwestern Washington. Despite the scale and economic impact of the raspberry industry, a microscopic nematode poses a significant threat to growers. This nematode is Pratylenchus penetrans, more commonly referred to as root lesion nematode (RLN).

Root lesion nematode is a migratory endoparasitic nematode that spends its life in both the soil and plant roots. It is inside those fine roots where it feeds and causes damage leading to reductions in plant productivity, and in extreme cases, plant death.

Raspberry growers have struggled to successfully manage RLN since the phase out of methyl bromide. Fumigant alternatives to methyl bromide have been inconsistent and sometimes ineffective at controlling RLN. Furthermore, post-plant management options are limited and have not been shown to be very effective across a wide range of situations. Viable solutions for RLN

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management were needed by the raspberry industry to protect their high-value crop from this destructive nematode.

samples should be collected near the crown of the plant and to a depth of 12 to 18 inches.

In response to growers’ needs, researchers teamed up across institutions with the goal of generating information and data-driven management practices that would allow growers to successfully manage RLN. This research started approximately eight years ago and the information generated now allows growers to manage RLN based on knowledge of RLN biology, at-planting population densities, soil type, and fumigant chemistry and application methods.

Action thresholds for plant-parasitic nematodes in perennial fruit crops are challenging to generate because perennial crops like raspberry can compensate for nematode parasitism depending on their internal physiological state and/ or environmental conditions. However, McElroy (1992) generated guidelines for soil samples. These thresholds suggest management should ensue if pre-plant soil populations are >250 RLN/250 cm3 or post-plant populations are 500 to >2,000 RLN/250 cm3.

Determine Population Densities Growers can collect soil or root samples to get an estimate of RLN population densities in their field. This can be helpful in determining if densities are low, medium, or high, which will inform future management practices. Although soil samples are typically collected by growers, they can often underestimate population densities. Root samples are more reflective of population densities and they should be collected before the planting is removed for renovation to ensure the roots are alive and contain nematodes. Regardless of sample type,

November/December 2018

Importance of Soil Type Raspberry is commonly grown on sandy loam to loamy sand soils. Soil type and proportion of sand has been shown to influence RLN distribution in the soil profile. Therefore, it is important to understand where nematodes reside in soil and how fumigants will behave in different soil types.

Research has shown RLN resides predominately in the top 18 inches in high sand content soils (70 percent sand), whereas they reside deeper in

the soil profile with decreasing sand content (e.g. 50 percent and below) (Kroese et al., 2016). Furthermore, soil type influences fumigant efficacy. High sand content soils where RLN resides at more shallow depths respond better to shallow applications of fumigants.

In this situation, shallow applications of Vapam (metam sodium) would be a good approach. For heavier soils where RLN resides deeper in the soil profile, deep-shank applications of 1,3-dichloropropnene (1,3-D) containing products are appropriate.

Compound Selection There are only a few fumigant compounds that are registered and effective against RLN. One of the most widely used compounds is 1,3-D, which is a nematicide and is often mixed with chloropicrin that has fungicidal activity.

A common 1,3-D containing fumigant that raspberry growers use is Telone® C-35 (65 percent 1,3-D:35 percent chloropicrin).

Increasingly growers are using metam sodium (e.g. Vapam), which liberates methyl isothiocyanate when exposed to water. Methyl isothiocyanate is an organosulfur compound that has nematicidal activity.

Metam sodium it is less expensive and has smaller buffer zones than fumigant products that contain chloropicrin. It also has a broader spectrum of activity. Metam sodium can be injected at shallow depths, which can be a benefit or downfall of the application method depending on soil type and where RLN resides in soil.

A few other fumigant products are

available to growers, including Basamid (another methyl isothiocyanate liberator) and Dominus (allyl isothiocyanate).

These products have smaller buffer zones, but efficacy has been variable and likely attributed to limited soil mobility.

valleyways and re-colonization of roots in raised beds is negligible (Walters et al., 2017). Furthermore, bed fumigation has outperformed broadcast fumigation in terms of RLN suppression in many trials.

Broadcast or Bed Fumigation?

One caveat with bed fumigation is that it may not be effective for soilborne diseases that are able to travel through water, such as Phytophthora root rot.

This could be particularly problematic in fields that experience flooding. This potential scenario underscores that knowledge of the field site and its history can also be powerful in informing management decisions.

Raspberry growers traditionally broadcast fumigated their fields. Now, however, an increasing number of acres are bed fumigated. Bed fumigation provides many benefits over broadcast fumigation and can improve RLN management. Less fumigant is applied on a per area basis because only raised beds are fumigated, which in turn reduces fumigant buffers. There is currently a global shortage of Telone, therefore, bed fumigation will allow for more acreage to be fumigated with Telone relative to broadcast fumigation.

Because alleyways are untreated with bed fumigation, growers were concerned that RLN may move from alleyways to their raised beds and subsequently infect newly planted raspberry plants. However, results from field trials have shown few RLN reside in

Tarps Tarps are agricultural films that are totally impermeable or virtually impermeable (TIF and VIF, respectively). Tarps are strongly recommended for fields with high RLN population densities or a history of other soilborne diseases, as they enhance fumigant efficacy by retaining a fumigant in the soil longer. Tarps also qualify for buffer zone

Continued on Page 6

Photo courtesy of Lisa DeVetter November/December 2018

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Registered Fumigants Fumigant

Pro

Telone C-35 (65% 1,3D:35% chloropicrin)

§ §

Con

Targeted towards nematode control Growers are familiar with this product

§ § §

Buffer concerns with chloropicrin Not as effective against root rot pathogen (P. rubi) Cannot be broadcast applied

Pic-Clor 60 (40% 1,3-D: 60% chloropicrin)

§

Targeted towards P. rubi

§ § §

Buffer concerns with chloropicrin Not as effective against nematodes Limited efficacy data on this product in raspberry

Vapam/K-pam (metam sodium/potassium, methyl isothiocyanate liberators)

§ § §

Inexpensive Smaller buffer zones Broad-spectrum

§

Shallow injection, potential lack of control deep No commercial application available

Basamid (dazomet, methyl isothiocyanate liberator)

§ § § §

Inexpensive Smaller buffer zones Broad-spectrum Used in Canada

§ §

No custom application available Control results in other production systems have been variable

Dominus (allyl isothiocyanate)

§ §

Small buffer zones Broad-spectrum

§ § §

Limited mobility in soil Expensive Limited efficacy data on this product in raspberry

§

Alternatives to Fumigants

has been an active area of research for many cropping systems. In northwestern red raspberry, we have studied application of brassica seed meals, solarization, and different cover crop management practices. While some of these alternatives have worked in fields with low- to medium-RLN infestations, they do not have the reliability of soil fumigation. Additional research efforts are needed to find cost effective management strategies for RLN, which would benefit growers that would prefer not to fumigate their fields.

Alternatives to chemical soil fumigants

Plant Resistance

Continued from Page 5 reduction credits and listed by active ingredient(s) (see https://www.epa.gov/ soil-fumigants/tarps for more information). Research to date has underscored the value that tarps can have in reducing RLN population densities compared to untarped fumigation. Although tarps add cost to the expense of fumigation, the additional expenditure can be worthwhile.

Photo courtesy of Inga Zasada 6

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Our research has demonstrated that all of the raspberry cultivars commonly planted in northwestern Washington are susceptible to RLN (Zasada et al., 2015).

This leaves growers with no options to use plant resistance to manage RLN.

portant time to implement RLN management practices, sometimes pre-plant management efforts are unsuccessful and growers need additional tools to try to keep RLN in check. Unfortunately, it appears that many new nematicides are not effective against RLN in raspberry. Trials with Nimitz, Salibro, and Velum Prime applied to newly planted raspberry and in the year following planting demonstrated the inability of these compounds to reduce populations of RLN. While speculative, either RLN is protected from these contact nematicides by the root or these compounds are not toxic to RLN. However, Vydate (oxamyl) can be applied to non-bearing raspberry and has shown efficacy (Walters and Zasada, 2017). Efficacy is likely maximized in fields with low RLN densities, so fields with higher densities will need to consider other or combined RLN management approaches.

Post-Plant Management

Research Goes On…

Even though pre-plant is the most imNovember/December 2018

While collaborating scientists have

Photo courtesy of Lisa DeVetter made progress in better understanding RLN in the red raspberry productions system and generated data-driven recommendations, the research continues.

The fumigant landscape continues to evolve and growers increasingly need more information on how to optimize

management of this significant plant parasitic nematode. Collaborations between researchers and raspberry growers will continue to be imperative and allow problems to be addressed, helping to ensure the continued vibrancy of this important agricultural industry.

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A decision-aid tool has been generated that synthesizes information about nematode and soilborne disease management for raspberry. It may be accessed at: http:// www.nwberryfoundation.org/ SFU/2017/September%20Special%20 Edition%20SFU.pdf

Disclaimer Statement For any of the pesticides mentioned in this article, be sure to read the label for specific rates and application recommendations.

References: Kroese, D.R., J.E. Weiland, and I.A. Zasada. 2016. Distribution and longevity of Pratylenchus penetrans in the red raspberry production system. Journal of Nematology 48(4):241-24.

McElroy, F.D. 1992. A plant health care program for brambles in the Pacific Northwest. Journal of Nematology 24(3):457-462.

Walters, T.W., M. Bolda, and I.A. Zasada. 2017. Alternatives to current fumigation practices in western states raspberry. Plant Health Progress 18:104111.

Zasada, I.A. and T.W. Walters. 2016.

Effect of application timing of Oxamyl in nonbearing raspberry for Pratylenchus penetrans management. Journal of Nematology 48:177-182.

Zasada, I.A., J.E. Weiland, Z. Han, Z., T.W. Waters, and P. Moore. 2015.

Impact of Pratylenchus penetrans on establishment of red raspberry. Plant Disease 99:939-946.

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Postharvest Irrigation Management for Vineyards By: Cecilia Parsons | Associate Editor

M

eeting the water needs of grapevines during the growing season ensures fruit quality and yields. Postharvest irrigations provide the fuel for next season’s harvest.

Fresno County’s new University of California Cooperative Extension (UCCE) viticulture farm advisor, George Zhuang said research has shown that vines require about ten percent of their seasonal water requirements following harvest.

Given the wide range of harvest dates for table, wine and raisin grapes, and different soil types and growing conditions, grape growers need to determine a specific postharvest irrigation amount based an those factors and current weather conditions.

Grapevines Need Carbohydrate Reserves

All photos courtesy of Cecilia Parsons

Grapevines need carbohydrate reserves in permanent wood structures for respiration during dormancy and to fuel new growth the following season.

Zhuang said adequate irrigation helps the vines produce carbohydrates and take up mineral nutrients. Soils need to be moist in order for nutrients to move from the soil into the roots. Leaves need to be hydrated and able to transpire to move nutrients from the root zone to

the woody tissues of the grapevine. It is also important to have leaves that are photosynthesizing (producing sugars in the leaves from carbon dioxide in the air). Vines are not using the carbohydrates produced after harvest for shoot growth or fruit development and therefore can be stored in the roots and trunk.

Postharvest Water and Nutrients Low levels of water and nutrients at the end of the season can yield unwelcome results at the start of next year’s growing season. Research has found that uneven bud break, poor and uneven shoot growth, poor set and a higher incidence of winter injury occur due to water and nutrient deficiencies that are not addressed after harvest. Fresno County’s UCCE’s Vine Lines said poor winter rainfall coupled with lack of postharvest irrigation can exacerbate erratic growth patterns.

On average, a traditional flood irrigated

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raisin vineyard has gone two months without irrigation postharvest. Wine grape vineyards, depending on harvest date and variety may go unirrigated in the weeks leading to dormancy.

Vineyards in sandy soils will also lose soil moisture at a faster rate than clay soils. Vineyards in finer textured soils may not show stress. With these conditions, it is advisable to use soil moisture monitoring devices to determine water needs. Besides soil type, factors to consider when making late season irrigation decisions include trellis type and canopy size, rootstock, age of vineyard, pest pressure, time of last irrigation and weather conditions post harvest.

Zhuang said that wine and raisin vineyards in the San Joaquin Valley typically receive about two acre feet per year and that ten percent of that should be applied postharvest. Table grape vineyards, depending on canopy size, usually receive from three to four acre feet per year with ten percent applied postharvest, depending upon time of harvest. More water may be needed, he said if leaching of salts below the root zone is necessary.

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Growers struggle with dry winter weather, Zhuang said, as they need to manage water and nutrient uptake to avoid damage to roots. Even using poor quality groundwater, he said, is better than water stress.

They just need to increase the amount of water applied.

In wet years, he said, there is no proof that overwatering will affect the quality of that year’s grape crop. In dry years,

research has shown that under-irrigation will reduce yield.

Dr. Larry Williams, professor emeritus at UC Davis Department of Viticulture and Enology, in a recent presentation to Sun Maid Growers, said a postharvest irrigation is beneficial for the overall health of the vine. That health can influence the growth of the shoots next year and may affect cluster primordia and flower development the following spring.

If the vineyard is irrigated postharvest and rainfall is minimal during vine dormancy Williams said, you may wait until vines are active—just before bud break—to irrigate. In his presentation, Williams outlined how much rainfall during the winter months contribute to the water requirements of a vineyard in the San Joaquin Valley.

Grapevines Irrigated at Full ETc Thompson Seedless grapevines were irrigated at full ETc during the 2013 season at the Kearney Agricultural Research and Extension Center. Irrigation was terminated November 11, 2013 and soil water content on November 12, 2013 was 15.16 percent vol./vol. Soil water content on March 14, 2014 was 15.44 percent vol./vol. The increase in soil water content was about 1 inch (23 milliliters) equivalent to 45.3 gallons/ vine. Reference ET (evaporative demand) during that period was 200 milliliters or 7.9 inches. This would illustrate that water can be used in your vineyard during dormancy if one has a cover crop or weeds between rows leaving less water in your vineyard due to minimal precipitation.

Irrigation after harvest maintains leaves in a healthy state. Vines need to have functioning leaves in the period between harvest and dormancy, Williams said. Once the leaves are lost as the vines go dormant, the vines rely on stored carbohydrates from that point until right before bud break. The leaves also store nitrogen which can be re-mobilized into the vine and held into

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Continued from Page 9 reserve until spring when it is needed for growth.

N at Harvest

Williams said about 50 percent of the nitrogen (N) in the leaves at harvest will remain in the leaves that fall from the vine but that also means that the other 50 percent was translocated back into the permanent structures of the vine. The translocation of N from the leaves between harvest and end of season accounted for 85 percent of the N accumulated in the trunk and roots after harvest. This percentage of nitrogen going back into the roots and trunk from the leaves may not occur for all grapevines.

be irrigated when winter rainfall is minimal, regardless of soil type. Assuring that at least one-third of the soil profile is re-wetted by mid-December will also help minimize the effects of cold damage.

Nitrogen may be translocated from the permanent structures of the vine—the trunk early on and the roots later—to the shoots.

The reserves may supply 10-25 percent of the total N needed for shoot growth at some point during the growing season.

From bud break to fruit harvest, N reserves only contributed 11 and 4 percent of the shoot N needed across two of the growing seasons.

A winter irrigation when rainfall is less than an inch during the months of November and December is advised by UCCE farm advisors. Mature vineyards maintained on drip irrigation don’t suffer fluctuations between wet and dry soils. As a result, they can begin storing carbohydrates during harvest, reducing water stress.

One- to three-year-old vineyards should 10

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November/December 2018

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Tomato Powdery Mildew: Managing the Disease to Minimize Impacts and Avoid Fungicide Resistance By: Brenna Aegerter | UCCE Farm Advisor for San Joaquin County

M

ildew problems in tomatoes have been somewhat less in recent years, but it continues to be a perennial problem in some of the production regions, particularly in the northern San Joaquin Valley and Delta areas. Tomatoes are plagued by not just a single powdery mildew pathogen, but actually by three distinct powdery mildew species. The primary mildew pathogen of field-grown of tomatoes in Central California is Leveillula taurica (note that the name Oidiopsis sicula refers to the conidial stage but is not commonly used). Leveillula taurica mildew was first reported in 1976 on tomatoes from

Imperial County, California and by the mid-1980s was found on tomatoes in all of the major tomato-growing regions of the state. In 1995, a second species causing mildew on greenhouse tomatoes in California was discovered and was later described as Oidium neolycopersisci. Apparently it was introduced into the US and Canada in the 1990s but its origin is not known. In addition to affecting greenhouse-grown tomatoes, this second species can also be a problem in California coastal-grown tomatoes. Finally, in 2015, we saw new and unusual symptoms of powdery mildew sporulation on tomato stems and petioles in

Figure 1. Bright yellow chlorotic spots which progress to necrosis are typical of mildew caused by Leveillula taurica.

Sporulation, visible here, may or may not occur.

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open field production near Stockton.

From these fields we identified a third mildew species, Oidium lycopersici, which previously had only been reported from Australia. Today, three years after its initial appearance, Oidium lycopersici still appears to be restricted to tomatoes grown in the Sacramento, San Joaquin Delta and areas east of Stockton. It may be that the slightly cooler microclimate of this region is particularly suitable to this species. Alternatively, there may be an unknown alternate/ over-wintering host plant which is more abundant in this region. This article will focus on mildew caused by Leveillula

All photos courtesy of Brenna Aegerter

in open field production systems in the Central Valley of California, with some references to the less common pathogen, Oidium lycopersici.

Powdery Mildew Caused by Leveillula Powdery mildew caused by Leveillula is somewhat different from the typical mildews in other crops such as grapes, cucurbits or cherries for example. These more typical, Oidium-type mildews grow superficially, producing mycelium and spores on the upper leaf surface, with only small, specialized structures called haustoria penetrating the leaf cuticle to acquire nutrients from the plant. In contrast, Leveillula grows within the leaf tissue, with its mycelium growing between leaf parenchyma cells; this is referred to as endophytic growth.

Inside the leaf, it has a latency period of up to 21 days before symptoms may be visible. The latency period refers to the time from infection to symptoms, and will vary with the temperature. This means that by the time you can see leaf symptoms, the fungus may already have achieved extensive mycelial growth inside the leaves. This potentially long latency period explains, in part, why this disease can be so challenging to scout for and control. Furthermore, the mycelium inside the leaves is protected, to some degree, from contact materials such as horticultural oils, potassium bicarbonate, and even many conventional powdery mildew fungicides that might be more effective against Oidium-type mildews. Another difference between Leveillula and Oidium mildews is that Leveillula colonizes neither petioles, stems nor fruit, infecting and colonizing only the leaflets of the compound leaf.

to a light microscope, a simple mount can be made by touching the sticky side of a small piece of clear tape to the underside of a suspect lesion and then placing the tape sticky side down on a drop of water on a glass slide and examining it under the microscope. Leveillula makes distinctive spores of two types: one type cylindrical and the other type pyriform (tapered at one end). However, rather than relying on microscopic examination, Pest Control Advisors (PCAs) and consultants more commonly perform a field diagnosis by quickly learning to recognize the unique, bright yellow spots, which can resemble yellow paint splashed on the leaves (Figure 2, below). Note that more diffuse leaf

chlorosis or yellowing can of course be caused by a multitude of different problems, as well as normal leaf senescence, and should not be attributed to mildew.

Powdery mildew typically appears first on the oldest leaves and down in the interior of the tomato canopy. However, as the disease progresses it can move upward and outward through the canopy, even damaging newer leaves and those near the top of the canopy.

Typical Symptoms Prior to late summer 2006, typical symptoms of L. taurica mildew began with yellow spots followed by very

Continued on Page 14

Spores Spores (conidia) of L. taurica may be sparse to abundant on the leaf and can be formed on either the upper or lower leaf surfaces. When abundant, it can resemble an Oidium-type mildew, with the noticeable powdery white sporulation for which this group was named (Figure 1, left). When sporulation is sparse, it can be difficult to see spores even with a hand lens. If you have access

Figure 2. Bright yellow spots typical of infection by Leveillula taurica

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Continued from Page 13 sparse sporulation on the undersides of the leaves. Today, it seems that the symptoms and signs are more variable, as the sporulation may precede the yellowing, or the yellow lesions may never appear. Since 2006 we also observe that the sporulation can be more abundant and may be visible on the leaf tops, undersides, or both sides. Regardless of whether it begins with yellow spots or with powdery white sporulation, the spots enlarge and turn necrotic. As the disease progresses, these necrotic spots coalesce until the entire leaf is affected (Figure 3, below). The leaves do remain

attached, but are so dried out that the effect is the same as defoliation. The loss of canopy and exposure of the fruit can lead to sunburn, especially when temperatures are high. It is worth noting, however, that drying of the foliage and loss of canopy cover in processing tomatoes in the weeks just prior to harvest may have no impact on fruit yield and may, in fact, be of some benefit by lowering the humidity in the vicinity of the ripe fruit and therefore reducing the risk of blackmold fruit rot caused by Alternaria alternata. On the other hand, earlier defoliation may increase sunburning of fruit which in turn predisposes the fruit to infection by Alternar-

ia. Thus, as harvest approaches, we need to worry less about mildew.

When not sufficiently controlled, L. taurica mildew has been blamed for losses of tonnage and soluble solids. In field trials conducted by University of California (UC) advisors throughout the Central Valley, a significant yield loss was observed in only two out ten trials (20 percent) conducted over four years with variable disease pressure. Both were instances where the powdery mildew started more than one month prior to harvest and built up to significantly damaging levels. However, in nine out of the ten trials (90 percent), mildew did have a significant impact on soluble solids, even when it damaged the foliage only in the last month. On average, powdery mildew reduced soluble solids at harvest by 0.6 ºBrix.

Weather Although L. taurica is well-adapted to our warm, arid climate, it does not do well when temperatures exceed 86°F, and even short periods of a few hours over 95°F can suppress disease development under controlled conditions. So while heat waves can cause other problems for the tomato crop, at least they suppress mildew! On the other hand, tomato powdery mildew also does not seem to do well in very cool summers, presumably because growth and colonization of leaves is slowed with cooler temperatures. In the 1990s, a model was developed that used in-field weather stations to predict disease and guide fungicide spray timings. However, UC advisors conducted validation studies over three years and found that the model was not very reliable. In general, in the early season it called for sprays that were usually not warranted (likely due to the fact that the spores were not yet in the air), while later season is sometimes failed to call for sprays that were in fact warranted. We recommend that spray timings be based more on careful scouting, and recognition of whether mildew is active in a geographic area.

Figure 3. Necrotic lesions caused by powdery mildew may coalesce, killing leaflets

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Optimizing Chemical Control To optimize chemical control, fungicide applications should begin at the very first sign of disease in a field, or even before you see symptoms if weather conditions are favorable and the disease is active in the region (thus spores are likely in the air). In our production system, tomatoes seem to become susceptible to Leveillula beginning around

five to six weeks after transplanting, although Oidium may cause problems even earlier in the crop development.

Once an outbreak is established in a field, it can be very challenging to appreciably slow the disease. Thus, an emphasis should be made on applications early in the outbreak or even before symptoms are observed. In particular, late-planted tomatoes face higher disease pressure periods from mid-July through September, and a calendar-timed application at six weeks

for Biological Controls N .O . W., , ia r a n r e lt A , se o Anthracn and more .. .

after transplanting may go a long way to preventing outbreaks. We have noticed that the newer, less common Oidium mildew may get started in June, which is earlier in the summer than we typically see Leveillula problems.

Maximize the utility of fungicides by getting the best coverage possible. In most cases, this means spraying by ground. However, it is well accepted that sulfur dust applied by air provides good control due to the ability of the dust to penetrate the canopy and its subsequent fuming activity once deposited there.

Applying other sprayable fungicides by air may result in reduced product performance due to poor penetration of the canopy by low-volume sprays.

Over the course of a decade, California tomato growers have made a shift towards ground rig spraying of fungicides (vs. air applications)—as well as a shift towards sulfur dust over sprayable or wettable sulfur products. From my analysis of the Department of Pesticide Regulation Pesticide Use Reporting (DPR PUR) database, I found that more California tomato acreage is now being treated with sulfur (acreage up 40 percent from 2006 to 2015). However, there is a greater use of dust now versus sprayable sulfur (the proportion of sulfur applied as a dust is up 26 percent over sprayable sulfur) and greater use of ground application of fungicides versus air (from 18 percent of acres treated by ground in 2006 to 58 percent of acres treated by ground in 2015). The adoption of ground-rig sulfur dusters has been very apparent in the northern San Joaquin Valley. This shift towards sulfur and towards ground applications, driven by the transition to buried drip irrigation, has benefited mildew control programs greatly.

Fungicide Resistance

m ar ro n eb io .co m 16

Progressive Crop Consultant

November/December 2018

As a group, the powdery mildew fungi are considered to have a high potential to develop resistance to fungicides. This means that the more we use a particular group of fungicides against mildews, we select for individuals which possess a reduced sensitivity to that particular mode of action. Over time, the

pathogen population shifts towards a higher proportion of these less sensitive individuals. Eventually, when these individuals make up enough of the population, this can manifest in the field as a weakening or loss of chemical control.

Sometimes this can be qualitative or black-and-white difference (e.g., the fungicide no longer works at all), but more often the resistance we observe in tomato powdery mildew is quantitative, meaning that the fungicide may still work, but may not be as effective as it was before pathogen exposure to it. You might say that the pathogen population has become “less sensitive to” or “more tolerant of ” the fungicide. In some cases, not using the fungicide class for a period of time will allow the pathogen population to revert back to its former, “fungicide sensitive” state. This can happen when the change that confers the reduced sensitivity has some sort of fitness penalty for the fungus. In other cases, the resistance is “fixed” and the population will remain fungicide-resistant even if the class of fungicide is no longer used.

The newer classes of fungicides, while very effective, have very specific modes of action and are at a much higher risk for developing resistance than the older classes of fungicides. Recent research conducted by the Dr. Ioannis Stergiopoulos and colleagues at UC Davis sheds some light on the development of fungicide resistance in the tomato powdery mildew fungus. We collected numerous Leveillula isolates from commercial tomato fields in the Central Valley. Genetic analysis of these isolates shows us that this fungus does display genetic evidence of exposure to QoI or strobilurin fungicides. They detected differences in the gene that codes for the target binding site where strobilurin fungicides act on a fungal enzyme that is critical for mitochondrial respiration and thus energy production in the fungal cells. So indeed, our use of strobilurin fungicides does seem to be selecting for less sensitive individuals.

However, so far these fungicides are still effective against tomato powdery mildew. Knowing that this selection process is already underway, it is even more critically important that we employ best

practices to prolong the useful life of the fungicides we have.

These practices include: •

Utilize cultural practices that reduce disease pressure. In the case of powdery mildew, this might mean selecting less susceptible tomato cultivars, or managing the crop to minimize stress, etc.

PISTACHIOS

•

For medium to high risk fungicide products (see table for categorization), use the products preventively or at the early stages of disease development. Also, don’t stretch treatment intervals too long when there is disease pressure.

•

Optimize your chemical applications. When spraying or dusting, use best practices to ensure optimal canopy coverage (e.g. using sufficient water volumes, correct nozzle selection and operating pressures, and making applications by ground). Your applications need to be effective to reduce the risk of resistance development.

•

•

When using fungicides, rotate between products in different chemical classes, or use tank-mixes or formulated pre-mixtures that contain fungicides from two different classes and which are both active against the target pathogen. For tomato powdery mildew, I recommend including sulfur dust as part of your rotation program.

Always follow label restrictions regarding resistance management. These are designed to limit the number of applications within a season to reduce the risk.

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17

5/11/17 4:17 PM

FRAC Group Code

Chemical Group Name

Trade Names

Common Names

Relative Efficacy Against Leveillula Mildew in Tomato

Risk of Resistance Development

11

Strobilurins, (Quinone outside inhibitors, QoI)

Quadris Flint Cabrio

azoxystrobin trifloxystrobin pyraclostrobin

+++ no data ++

high – follow label restrictions

7

Carboxamides (Succinatedehydrogenase inhibitors, SDHI)

Fontelis

penthiopyrad

++

medium to high

3

Triazoles (Demethylation inhibitors, DMI)

Rally Rhyme Inspire

myclobutanil flutriafol difenoconazole

++ +++ no data

medium

11 + 3

QoI + DMI

Quadris Top

azoxystrobin + difenoconazole

+++

presumably lower risk than individual components

7 + 11

SDHI + QoI

Priaxor Luna Sensation

fluxapyroxad + pyraclostrobin fluopyram + trifloxystrobin

+++ +++

presumably lower risk than individual components

B6

aryl-phenyl-ketones

Vivando

metrafenone

++

medium

U06

unknown

Torino**

cyflufenamid**

+++

one case of resistance in another pathogen, resistance management required

M02

inorganic

various products

sulfur

+++ (dust) ++ (sprayable)

generally considered low risk

F6

microbial (Bacillus)

various products

Bacillus amyloliquefaciens strains

+ (limited data)

resistance not known

+ (limited data)

resistance not known

material of biological origin Not classified

plant extracts, etc. various products

inorganic salts

potassium bicarbonate horticultural oils

mineral oils

Continued from Page 17 In Table 1(Shown above), the group number refers to the FRAC (Fungicide Resistance Action Committee, see www.frac.info) grouping. This categorization is based on the mode of action of the fungicide. As you can see, we now have products registered for use on tomatoes which come from a number of different classes with varying modes of action, which helps us immensely when developing a resistance management plan. When selecting a fungicide, you may also want to consider other pest pressures. For example, sulfur dust has the benefit of also being one of the best materials for managing russet mites, thus making it a good choice for applications in early to middle stages of crop development. However, some 18

Progressive Crop Consultant

of the sprayable fungicides have efficacy against blackmold fruit rot, so that should be a consideration for late-planted tomatoes which may encounter a risk of fruit rot in the fall.

Table 1. Materials for powdery mildew control, categorized by their FRAC code. Always check registration status of materials prior to use.

Acknowledgements I thank the California Tomato Research Institute for funding research on tomato powdery mildew, as well as the chemical manufacturers. Thanks to Scott Whiteley, Daniel Rivers, Shirley Alvarez and Cheryl Gartner for technical assistance with field trials.** California registration for tomato pending

November/December 2018

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19

Safe, Profitable, and Practical Label for Sustainable Production and Food Security By: Surendra K. Dara

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

All photos courtesy of Surendra K. Dara.

Santa Maria strawberry grower, Dave Peck, Manzanita Berry Farms.

This article is sponsored by

D

ifferent people have defined sustainable agriculture or food production refers to the farming systems that maintain productivity indefinitely through ecologically balanced, environmentally safe, socially acceptable, and economically viable practices. It is a system that ensures food security for the growing population of the world by taking science, economics, human and environmental health, and social aspects into consideration.

Agriculture Through the Ages Agriculture has evolved over thousands of years from subsistence farming, meeting the needs of individual families to agribusiness catering to the needs of consumers around the world. Arthro20 Progressive Crop Consultant

pod pests, diseases, and weeds (hereafter referred to as pests) have been an issue all along, but their management went through cyclical changes. In the modern ages, pest management initially started by using naturally available materials such as sulfur or plant-based pyrethrums that gradually evolved into using toxic pesticides of natural or synthetic origin. While pesticide use improved farm productivity and food affordability, indiscriminate use of synthetic broad-spectrum pesticides in mid 1900s led to serious environmental and human health issues. Pesticide use regulations, discovery of safer pesticides, and new non-chemical alternatives, in the past few decades, have improved pest management practices to some extent. However, large quantities of synthetic chemical pesticides are still used in conventional farms for managing a variety of pests to prevent yield losses and optimize returns. Lack of good agricultural practices or integrated pest management (IPM) awareness has also contributed to excessive use of chemicals and the associated risk of resistance in pests and environmental contamination. In some developing countries, or countries where pesticide use is not

November/December 2018

strictly regulated, highly toxic pesticides are used very close to the harvest date (or even after harvesting), causing serious health risks for consumers.

While pesticides helped reduce crop losses, synthetic fertilizers significantly improved crop yields and returns.

Excessive application of fertilizers, however, leads to a number of problems including increased vulnerability of crops to pests and diseases and environmental toxicity through ground water contamination or negatively affecting soil microbiome.

Under these circumstances, in recent years, consumer preference for chemical-free food gave impetus to organic production; thus, the acreage of organically produced fruits, vegetables, and nuts has been gradually increasing.

Many stores now promote and sell fresh or processed organic foods, at premium prices, to those who can afford them.

While organic farming is generally considered more challenging and less productive, growers are willing to take the risk as they try to meet the market demand and maintain their market share of organically grown produce.

Continued on Page 22

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Continued from Page 20

IPM Approach

However, managing weeds in organic farms continues to be a labor-intensive and expensive part of production.

Labor shortage in many areas exacerbates manual weed control. In some crop and pest situations, control of pests with organically acceptable tools is not sufficient. Unmanaged pest populations can spread to other areas and/or crops, cause higher yield losses, and indirectly contribute to higher pesticide use on neighboring conventional farms. When it comes to nutrient management in organic production, manure, compost, and other sources provide organic matter, in addition to nutrients, that improves soil structure and microbial activity. However, large quantities of some of these materials are needed to provide sufficient nutrition to meet the crop needs. Nutrient leaching can also be a big problem in organic farms if not managed well.

IPM offers an effective, practical, and sustainable solution where excessive use of chemical pesticides is limited, pest populations are effectively managed, and returns are optimized without having a negative impact on the environment. IPM is an approach where host plant resistance (selection of resistant cultivars), modification of planting dates, crop density, irrigation and nutrient management or use of trap crops (cultural control), conservation or augmentation of natural enemies (biological control), pheromones for mating disruption or to attract and kill (behavioral control), traps, netting, and vacuums (mechanical control), chemicals from various mode of action groups (chemical control), plant extracts (botanical control), and entomopathogens or their derivatives (microbial control) are used in a balanced manner. It is a comprehensive

Sanjay Kumar Rajpoot at the Santa Maria Strawberry Field Day in 2016.

Table 1. Comparison of various food production systems from the global perspective.

22 Progressive Crop Consultant

November/December 2018

approach where all available strategies are considered to achieve pest control with minimal impact on the ecosystem. However, many consumers are not aware of the difference between organic and conventional practices or IPM strategies. Many perceive organic farming as a pesticide-free production system and as the only alternative to conventional farming with synthetic chemicals and nutrients. Organic farming also uses pesticides, fertilizers, and hormones, but of natural origin.

For example, potassium salts of fatty acids are used against insects, mites, and fungal diseases. Mined sulfur is used as a miticide and fungicide. Popular organic insecticides, based on pyrethrins extracted from Chrysanthemum cinerariaefolium flowers, are very toxic to natural enemies, honey bees, and fish although they are less stable in the environment than synthetic pyrethroids.

The bacterium, Bacillus thuringiensis, which is the source of the toxic insecticidal protein in genetically modified corn, cotton, soybean, and other crops, is widely used in organic farming for

managing lepidopteran pests. Organic produce is also perceived to be healthier than conventional produce although several studies showed that there was no such difference. A thorough understanding of conventional, organic, and IPM-based production could influence consumers’ preference and allows them to make informed, practical, and science-based decisions. Conventional farming, in this context, refers to a system where it is more geared towards the use of synthetic compounds with a lesser emphasis on natural or biological approaches.

IPM encourages the use of all available control options in a manner that maintains productivity without compromising environmental and human safety. IPM-based food production can be a better alternative than organic production for various reasons (Table 1, Pg. 22).

sources of agricultural inputs, an ideal system would use a combination of both for economic viability, environmental and human safety, and social acceptability. Such a sustainable system will ensure profitability to the producers and affordability for all consumers while minimizing the health risks. Both natural and synthetic fertilizers can be used judiciously to meet the crop needs.

A sustainable production system allows the use of chemical pesticides to address critical pest issues when needed, without losing the focus on environmental safety and sustainability. Agriculture is a global enterprise and California agriculture leads and influences farming practices around the world. While food production with an organic seal can continue, shifting from conventional practices to production with an Sustainably Produced seal might be a safe, profitable, and practical approach.

Sustainable Crop Production

Additional Reading:

Considering the challenges and benefits associated with synthetic and natural

Dara, S. K. 2015. Producing with the seal of IPM is a practical and sustainable strategy for agriculture. UCANR eJournal Strawberries and Vegetables. http://ucanr. edu/blogs/blogcore/postdetail.cfm?postnum=19735 Gold, M. V. 2007. Sustainable agriculture: definitions and terms. USDA-NAL, Beltsville, MD. https://www.nal.usda. gov/afsic/sustainable-agriculture-definitions-and-terms#toc2 NPIC. 2014. Pyrethrins general fact sheet. http://npic.orst.edu/factsheets/pyrethrins. pdf Unsworth J. 2010. History of pesticide use. http://agrochemicals.iupac.org/index. php?option=com_sobi2&sobi2Task=sobi2Details&catid=3&sobi2Id=31

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

Jimmy Klick at the Santa Maria Strawberry Field Day in 2016

November/December 2018

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23

Spotted Wing Drosophila in Caneberries: A Ten Year Retrospective

By: Mark Bolda, UC Cooperative Extension, Santa Cruz County

Spotted wing drosophila male. Photo courtesy of Larry L. Strand.

S

ince its initial detection in North America in a field north of Watsonsville in 2008, spotted wing drosophila, Drosophila suzukii, a species of vinegar fly originally a native of Southeast Asia, has spread far across the US, Mexico, Europe and on into South America. A pest of many soft fruits, spotted wing drosophila has been especially damaging in caneberries, those being raspberries and blackberries, in California.

Much has been done and shared on the management of this introduced pest over the past ten years, and I think it will be very helpful to summarize it in a short and accessible format. The following article will look back upon the last ten years of researcher and grower experience on spotted wing drosophila (SWD) and attempt to distill the most important and usable information out of the effort that has gone on over this time.

SWD v Vinegar Fly What sets SWD apart from other vinegar flies is that rather than waiting for the fruit to be injured or start to rot to begin egg laying activity, it can actually damage fruit on its own. The female SWD lays her eggs into the fruit prior to its full maturation, rather than on the fruit’s surface as is the case with many of the other vinegar flies, and she has a serrated ovipositor (the egg laying organ) outfitted for that very purpose.

Generally, in the case of raspberries and blackberries, the bulk of this egg laying 24 Progressive Crop Consultant

takes place one or two days before harvestable ripeness of the fruit, even though some are laid later and some earlier. And there are a lot of eggs to be laid as generally an individual female will lay in the area of 200 eggs in her lifetime.

Once the eggs have been inserted into the fruit by the female fly, it is not many days before the larvae hatch and begin feeding. Many people think these larvae are feeding on the fruit tissue and juice, but they are in fact feeding on the yeast that has been introduced into the fruit when the egg was injected into it and is now growing and providing sustenance to the larva.

The larvae generally mature in less than two weeks, and will then pupate. Pupation in the laboratory takes places on the outside of the fruit or in some cases on the walls of the container. In the field however the situation is very different, and one seldom finds pupae on fruit hanging on the plant or on the leaves surrounding it. Instead, according to our recent investigation in raspberries, we have found that in the field pupae are found on the undersides of fallen fruit or a few millimeters below the surface of the soil.

Based on calculations of SWD adult flies taken in many vacuum samples using a hand held Bug vac, we estimate the average population of adults alone in a field is somewhere in the ballpark

November/December 2018

of 600,000 adults per acre, and this number concurs with the numbers of eggs and larvae found in fruit samples.

Program of Management As mentioned above, over the past ten years, a program of management has developed of sorts. It is, like most every other successful insect management program, an integrated approach deploying a variety of methods; chemical, cultural and mechanical.

1.

The use of chemical insecticides is a critical part of management of SWD. It is important to note however that even very efficacious materials such as zeta-cypermethrin and malathion have limited residual activity, meaning that adult flies which emerge from the protected pupae some time after the pesticide application will not be affected.

Furthermore, it is critical for growers and farm managers to realize that these adult flies are the only ones accessible for management.

The eggs and larvae are in the fruit and the pupae generally are on the ground, underneath fallen fruit.

All of these are nearly impossible to reach with standard pesticide application methods.

Efficacy tests and grower experi-

Continued on Page 26

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Continued from Page 24

apple cider vinegar traps worked best in the cooler months. Either of these two liquids can be placed in lidded cups with small holes punched in the top to limit escape and they should be frequently changed, in general every one to two weeks to keep and maintain their efficacy.

ence point to two weeks of efficacy with malathion and zeta cypermethrin, and less for spinetoram.

For the organically registered formulation of spinosad, duration of efficacy runs much less at 3 to 5 days, pyrethrin less than that. Pest managers and growers should pay attention to these intervals when thinking through how to bring down a population of SWD. Enhancements to the spray mix to attempt to increase efficacy, such as acidifying the water carrier or adding sugar to the tank mix so that flies ingest the pesticide, have not been met with success. The key to successful control of SWD in caneberries still lies with using effective chemistries and applying them correctly when the populations of SWD are still low and still manageable.

2.

3.

26 Progressive Crop Consultant

6.

The idea of predation and parasitization is a good one, but specialized parasitoids for SWD have not been generally recovered in commercial crop production settings in California but researchers are looking hard for others overseas in the native habitat this vinegar fly.

Some really valuable research work in Maine blueberries has observed predators such as ground beetles, ants, spiders and crickets feeding on the pupae. Larger predators such as birds one would think could have an effect, but my research assistant Monise Sheehan and I did work in 2016 and again in 2017 attracting large numbers of hummingbirds to areas with SWD with no discernible effect.

7.

Mechanical solutions such as large vacuums to remove flies from fruiting canes have not met with success. The use of exclusion netting however has worked to very much reduce larval infestation of blueberries in the United States. Although the effort would be on a much larger scale, the nets can be made compatible with tunnel system we use in California for caneberry production and would need to be placed before flies become very active in the early spring.

It should be noted here however that in this same study we found that larvae were already detectable in primary raspberry fruit several weeks before the first adult fly was discovered in a trap. That being said, the effort involved in collecting the fruit, holding it a few days to allow the larvae to develop and then looking for them in the laboratory makes this method less attractive for growers whose time and resources are limited.

4.

Since our initial work realized some efficacy of statistical significance at the same time exposure to the pesticide by bees and other beneficials was minimized, we were initially quite enthusiastic about the use of attractant bait sprays. However, on finding much greater efficacy in terms of numbers of adult flies reduced in the field through conventional and organic sprays, the relative attractiveness of these materials was reduced. However, the concept is still being explored, with work supported by the IR-4 program on a bait and kill approach this fall.

Trapping is a good way to know when the numbers of SWD are increasing in the field and it is time to take steps to control them. With University of California (UC) and University of California Cooperative Extension (UCCE) colleagues Monise Sheehan and Kelly Hamby, we did a good stretch of work testing traps over the period of two years, and arrived at the conclusion that yeast sugar water traps work best in the warmer months and the

the numbers of eggs and larvae surviving on the fruit.

5.

Sanitation has an important role to play in SWD management. In an unpublished replicated field trial with a local grower and his in-house scientist six years ago, I found that numbers of adult flies were in fact significantly decreased in areas where sanitation, that is removal of cull fruit from the field, was practiced. However, the numbers of adult flies were still high where sanitation was practiced and the amount of fruit damage in these areas was not acceptable. As such, sanitation should very much be a part of a farm’s SWD management program (especially in organic), but should be deployed in combination with a program of insecticide sprays.

Crop maturity and cooling. A very important tactic that growers have put to use in the field has been being careful about the maturity of fruit harvested. Fruit which is harvested even a day beyond marketable maturity has much higher odds of being infested with SWD eggs and should not be picked.

Additionally, prompt and extended periods of cooling at temperatures a little above freezing are a very important step to take in reducing

November/December 2018

In Conclusion The preceding has been a summary of the past ten years of research and grower approaches to managing spotted wing drosophila (SWD) in caneberries.

There are several pesticides mentioned in this article, and growers and managers should refer to labels before using any of these. For questions on this pest and other questions about caneberry production, one can contact UCCE farm advisor Mark Bolda at mpbolda@ucdavis.edu.

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27

Put Leaffooted Bug Monitoring on Your Winter and Spring To-Do List By: Kris Tollerup University of California Cooperative Extension Area-wide IPM Advisor Kearney Agricultural

Introduction

L

eaffooted bug, Leptoglossus zonatus (Dallas), (LFB) sometimes referred to as Western leaffooted bug, can cause considerable economic damage on almond and pistachio in the San Joaquin Valley. This bug is native to South and Central America; and North America, Mexico and the Southwest United States. However, over the past decade the range of LFB has expanded into areas in California as far north as Glenn and Butte counties. Leptoglossus zonatus feeds on several important agricultural crops important in the San Joaquin Valley including: citrus, corn, cotton, several nut species, peaches, pomegranate, tomato, and watermelon.

Economic Loss Most economic loss to almond and pistachio results from LFB feeding directly on the developing nuts. Early-season feeding on almond (March-May) and pistachio (May-June) results in epicarp lesions and/or nuts aborting and dropping from trees. Feeding after May and June in almond and pistachio respectively, cause dark stains on the nut meat surface and/or kernel necrosis. More-

All photos courtesy of K. Tollerup Figure 1. Adult leaffooted bug on citrus.

28 Progressive Crop Consultant

November/December 2018

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Continued from Page 28 over, LFB transmits the plant pathogens, Eromothecium coryli, that causes kernel rot in pistachio and stigmaqtomycosis of almond; and Neofusiccoum mediterraneum associated with panicle and shoot blight of pistachio. It is interesting to consider the host range of LFB and why the species does not cause a greater amount of economic damage to those crops. Tomato, for instance is a preferred host of LFB, yet PCAs and producers have not reported any

measurable loss. This could result from arthropod pest management practices in tomato, or simply that other crops are more preferred.

Primarily, the research has focused on better understanding LFB overwintering biology and behavior and development of an effective monitoring lure.

Research

Leaffooted bug belong to the Coreidae Family within the insect Order, Hemipteran. Commonly, members of this family produce a few different pheromones that aid in communication with other members of the same species. Research has shown that LFB produce aggregation, alarm, and sex pheromones. If the reader takes just a moment or two, surely, they can think of several examples of how exploiting a sex pheromone plays a major role in the management of insect pests. Mating disruption of moth pest such as codling moth, Oriental fruit moth, and navel orangeworm provide a few pertinent examples.

Since the early 2000s, the Almond Board of California, California Pistachio Research Board, as well as the University of California, have dedicated a considerable amount of money to developing better integrated pest management (IPM) strategies against LFB.

Pheromone-Based Monitoring

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Developing a pheromone-based monitoring tool for LFB has proven challenging. As far back as 2000, Wang and Millar, researchers out of the University of California (UC), Riverside outlined the mating behavior of LFB and found evidence that the males produce a pheromone that acts as an aphrodisiac i.e. a sex pheromone. Those researchers, however did not identify the compound. Fast forward about one-and-a-half decades and researchers out of the same lab at UC Riverside, have identified pheromone compounds likely important in LFB sexual communication. Field experiments evaluating some of the compounds began in 2017.

However, before such a lure becomes commercially available, it will likely take a few years for the researchers to work out the “bugs”.

Another approach to developing a monitoring lure has moved researchers toward utilizing plant volatiles. Several species of insects exploit odors given off by plants to locate a suitable food source for their offspring. Female navel orangeworm, for example cue into almond volatiles that consist of short-chain alcohols, and monoterpenes. Although there is strong evidence that the plant volatiles of almond, pomegranate, and pistachio play an important role in the ability of LFB to locate those hosts, specific compounds have remained elusive.

Continued on Page 32

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Continued from Page 30

Monitoring for LFB

Figure 2. Gummosis on almond due to adult leaffooted bug feeding during mid-April.

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If leaffooted bugs are found during monitoring, it is important to understand that a treatment threshold does not exist. Rather, a treatment decision includes several factors such as the number of bugs observed, location and amount of damage in the orchard i.e. at the orchard’s edge and very isolated, and history of LFB damage. Speak with your local UC Cooperative Extension Advisor or PCA for management options.

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November/December 2018

So, given the lack of a lure, how do we best monitor for LFB? In almond for example, the UC Pest Management Guidelines (UC PMGs) recommends monitoring for LFB during March and April by examining aborted nuts for gummosis or oozing on the nut surface. An important note is that if gummosis is found, it should be distinguished from a physiological disorder by cutting a cross section through the nut and looking for a puncture wound. The drawback to that method is that considerable damage can occur before detecting the bug.

Additional sampling methods that can be used in April and May include using a beat tray for mid-canopy sampling or a long pole to knock upper-canopy branches to startle adults, causing them to fly. Beat trays provide a useful tool for detecting nymphs but it indicates that adults have been present long enough to lay eggs and for the eggs to hatch. In other words, feeding damage has likely already occurred. Lastly, LFB very commonly feed on the sunny side and outer portion of the tree canopy. Search the sunny side of tree canopies for about 15 to 20 seconds per tree. Adults typically are feeding on nuts and are very easy to see.

Christeen Abbott-Hearn

Central and Coastal California 559.334.7664

Because of the importance of pomegranate in the lifecycle of LFB, an additional monitoring option exists.

This involves looking for overwintering aggregations around orchards, especially paying attention to the proximity of any pomegranate orchards and/or pomegranate hedgerows. Concentrate monitoring efforts on pomegranate during September through early November. If populations are observed, they will consist mainly of immature stages and can be managed i.e. killed

Continued on Page 34

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Continued from Page 32 before reaching the adult stage and dispersing to more secure overwintering locations. Insecticide use should occur only after considering the potential risks of the compound to beneficial organisms, including bees and biological control agents, and to air or water quality. For more information on these topics please consult the UC IPM Pest Management Guidelines for Almonds at http://ucipm.ucanr.edu > Agricultural pests > Almond

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

Figure 3. Late-instar leaffooted bug on pomegranat in early Nov. 2017

Figure. 3. Late-instar leaffooted bug on pomegranate in early Nov. 2017 Photo by K. Tollerup.

34 Progressive Crop Consultant

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36 Progressive Crop Consultant

November/December 2018