Pacific Nut Producer Magazine

Category: Pest/Disease Management

  • Treatment Options for Management of Walnut Scale and Frosted Scale

    Walnut scale (Figure 1) is an important economic pest of walnuts in California. High populations of walnut scale may affect tree vigor as well as predispose trees to diseases caused by several plant pathogenic fungi and possibly flatheaded borer damage. Historic UC Pest Management Guidelines emphasize the efficacy of insecticide applications at the crawler stage of insect development (late April to mid-May); however, with the introduction of new pest management tools such as insect growth regulators (IGRs), new studies have been conducted to evaluate the efficacy of these products at earlier times during the insect lifecycle. Both walnut scale and frosted scale overwinter as immature nymphs; therefore delayed-dormant application of IGRs has the potential to inhibit maturation and subsequent reproduction of these pests.

    In 2023, UC ANR and UC Berkeley researchers initiated a new collaborative study investigating the efficacy of four products applied at various rates and times (Table 1). Two insect growth regulator products, Esteem® (IRAC Group 7C) and Centaur® (IRAC Group 16), were included in the study, with both delayed-dormant (February 8, 2023) and crawler-stage (April 26, 2023) application timings. Centaur® was also investigated at two rates. Crawler-stage applications of Senstar® (a combination of spirotetramat and pyroxifin) and Assail 20SG® (a neonicitinoid) were also included in the study.

    Delayed dormant IGR applications inhibit maturation of walnut and frosted scale. Delayed-dormant application of Centaur WD® at either 34.5 oz/acre or 46 oz/acre reduced walnut scale survival by 81% of that of untreated control treatment by April. Both Esteem and Centaur reduced populations of mature frosted scale observed in late April by the over 85% of that on untreated trees (Figure 2).

    Crawler populations affected by IGRs and conventional insecticides. All treatments suppressed the rates of crawler emergence over time in comparison to the untreated control (Figure 3); however, delayed dormant applications of both IGR treatments (Centaur® and Esteem®) resulted in the highest suppression of the first-generation curve (Figure 3). Both rates of Centaur® applied during the delayed dormant period resulted in similar suppression of crawler emergence. Crawler stage application of Centaur® at the higher rate resulted in similar levels of crawler suppression as the delayed dormant IGR treatments (Figure 3). Moderate suppression of first-generation crawlers was observed with crawler stage treatments with the low Centaur® rate, Esteem®, and Assail® 30SG (Figure 3). Crawler stage application of Senstar® suppressed first-generation crawler emergence (Figure 3) and resulted in modest suppression (45%) of total crawler populations across the season as compared to the untreated control (Figure 4). All IGR treatments, regardless of the rate or timing, performed similarly with regard to total crawler populations across the season (Figure 4). The range in total crawler suppression across treatments of similar statistical significance was 88.2% (Centaur, 46 oz/acre, delayed dormant) to 54% (Assail, crawler stage), illustrating the variability in crawler counts in the orchard system (Figure 4).

    Summary. Delayed dormant applications of either of the insect growth regular products, Centaur® or Esteem®, offer excellent suppression of walnut scale and frosted scale populations. Delayed dormant applications may offer similar efficacy at lower product rates due to the opportunity to achieve better coverage prior to leaf-out.  Additionally, delayed dormant applications of these products may inhibit maturation of nymphs into adults, thus limiting sexual reproduction and subsequent laying of eggs.

    In prior studies, the efficacy of crawler stage Assail® application became apparent the year following application. Based on this background information, the populations of adult walnut scale will be evaluated across all treatments in April 2024 to fully capture the efficacy of these products over time.

    Additionally, future studies are planned to further determine the value of dormant versus delayed dormant applications of IGR treatments for management of walnut scale. The results of the current study, however, do demonstrate a need for updating the current UC IPM guidelines for management of walnut scale.  To date, the UC IPM guidelines only recommend crawler-stage applications of IGR products while the current study demonstrates the value of IGR applications earlier in the season. — By Elizabeth Fichtner, Mel Thayer, and Robert Van Steenwyk (UCANR)

  • New Stanislaus County Ag Commissioner Serves as Liaison Between Farmers and California DPR

    At Malcolm Media’s recent Tree & Vine Expo, event host Matthew Malcolm was pleased to introduce, Linda Pinfold, the new Stanislaus County Ag Commissioner to attendees.  Watch this brief video to get to know Linda and her emphasis on serving and assisting local farmers in navigating the ever-changing pesticide regulatory environment of California.

    Please thank this video’s sponsor Thunder Creek Equipment for their industry support.

  • New Invasive Pest Threatens Western Tree Nut Industry

    Western tree nut commodities just got through a very tough season, and markets are still less than ideal.  The last thing growers want to hear about is a new pest threatening their orchard production.  But the Carpophilus Beetle has already been under the radar far too long, damaging Central Valley orchards under the guise of “Navel Orangeworm.”  Watch this brief video with Bob Klein from the California Pistachio Research Board as he explains, and read more about this new pest in the December and January issues of Pacific Nut Producer magazine.

    Please thank this video’s sponsor Thunder Creek Equipment for their industry support.

  • State of the California Pest Control Adviser

    Pest Control Advisers (PCAs) in California are some of the brightest and versatile in the nation. They each generally cover a wide spectrum of crops grown under a many different conditions and pest challenges.  Watch this brief interview with Ruthann Anderson, President and CEO of the California Association of Pest Control Advisers, as she discusses the current State of the California Pest Control Adviser, as well as an opportunity for PCAs and their growers to get grant funding to tell their IPM stories. Learn more and apply at: https://capca.com/memberships/#study

    Please thank this video’s sponsor Thunder Creek Equipment for their industry support.

  • Increasing Presence and Damage of Brown Marmorated Stink Bug in Oregon Hazelnuts

    While hazelnut growers have been dealing with higher input costs and less than ideal nut prices, they cannot afford to cut costs on their pest monitoring and management practices.  An invasive pest, known as brown marmorated stink bug has taken a particular fondness of hazelnuts and is spreading across most of the major hazelnut growing regions of Oregon.  Watch this video interview with Oregon State University Entomologist Vaughn Walton as he provides insights on monitoring and controlling this pest and read more about it in Pacific Nut Producer Magazine. Don’t currently receive the magazine? Subscribe for free at: https://malcolmmedia.com/subscribe/

    Please thank this video’s sponsor George Packing Company for their industry support.

  • Bacterial blast/canker: What do we know?

    Diseases caused by Pseudomonas syringae can affect tissue throughout the entire tree, including bacterial blast of flowers, leaves, and shoots as well as bacterial cankers that develop under the bark in cambial and wood tissues of trunks, scaffolds, and branches. The pathogen commonly exists on plant surfaces in an orchard without causing disease, but cold, wet weather can trigger damaging infections. Bacterial canker/blast infections are most damaging, and potentially lethal, in stressed trees. Stress from ring nematodes or root-restricting hardpan predisposes almonds to blast and canker damage.

    The wet, cold spring of 2023 promoted widespread Pseudomonas bacterial infections in almond. This pathogen is becoming a consistent problem in cold, wet springs as almond plantings increase across the state.

    Currently, there are limited control options for bacterial canker/blast in almonds. The following list outlines factors influencing management practices and decisions.

    • Pseudomonas syringae is a damaging pathogen in cold, wet weather.
    • The pathogen is ubiquitous and occurs naturally on plant surfaces.
    • Infection risk varies with orchard site, rootstock, and variety selection.
    • Low spots (sites) are colder and thus, more prone to freeze damage.
    • Peach x almond hybrid rootstocks (Hansen, Nickels, Bright’s) are more vulnerable to ring nematode and subsequently to bacterial canker damage than Viking, Lovell, or Guardian rootstocks.
    • All almond varieties are susceptible to bacterial canker/blast infection, but some are more so than others. New self-fertile varieties are very susceptible to bacterial blast/canker.
    • Antibiotics can significantly reduce bacterial blast at bloom in almond, but none are currently labeled for almond. An effective, research-proven antibiotic (kasugamycin; Kasumin®) was available under Section 18 exception but is not currently labeled for almond.
    • Copper resistance is widespread in Pseudomonas syringae bacteria, making copper sprays ineffective.
    • Frost protection can help reduce damage.
    What can growers do to manage bacterial canker/blast?
    • If approved for use, treat with labeled antibiotic (for example kasugamycin; Kasumin®) 1-6
    • days ahead of forecast freeze. Expect only a week of protection. Note that very cold weather will damage buds even if an antibiotic is applied. Greatest economic benefit should come from bloom treatment.
    • If antibiotics are not labeled before bloom 2024, growers have limited options. Spraying copper to control bacterial canker/blast is generally ineffective. Adding mancozeb to copper may overcome resistance. Unfortunately, copper is phytotoxic and may cause leaf damage. Biologicals (Actinovate, Botector, etc) are not registered for blast control in almonds, but if applied for other bloom pathogens may reduce blast damage if applied multiple times (4, 3, 2, and 1 week before bloom).
    • Run frost protection irrigation if water is available. This will help reduce both frost damage and blast risk.
    • High rates (100 lbs urea/acre) of foliar lo-biuret urea in October reduced bacterial canker growth by more than 90% in UC studies in peach orchards. Lower rates of urea were not tested.

    In the long run, recognize bacterial blast and canker risk when selecting rootstocks and varieties for a colder site (valley floor, etc.). Almond variety and rootstock selections in the Sacramento Valley have changed, trending from more tolerant to more sensitive combinations. The traditional almond planting in the Sacramento Valley was Nonpareil and pollinators on Lovell peach rootstock – combinations generally tolerant to bacterial canker/blast. Trees on Marianna 2624 plum rootstock were much more susceptible to bacterial blast than those on Lovell peach. Newer rootstocks with a plum genetic background and newer varieties may also be more vulnerable to damage. Solid plantings of self-fertile varieties on certain newer rootstocks increase the risk of economic loss under cold, wet conditions.

    University of California researchers, funded by The Almond Board of California, continue to study Pseudomonas syringae bacterial infections of almond. Updates will be available at The Almond Conference (almonds.com/about-us/programs-and-events/almond-conference) this December. — By Franz Niederholzer, UCCE Farm advisor, Colusa, Sutter, and Yuba Counties

  • Varroa Mites and Deformed Wing Virus Make Honeybees More Susceptible to Insecticides

    The first of two apiaries, established in 2014 in Stoneville, Mississippi, provided honey bees for studying the impact of pesticides on honey bees. (Photo by Yu-Cheng Zhu, D5121-1)

    Controlling for Varroa mites, the parasitic mites that feed on honey bees and serve as vectors for viral diseases like deformed wing virus (DWV), can help with improving honeybee populations and make bees less susceptible to harmful insecticides, according to a recent study published in Environmental Pollution.

    Foraging honey bees may be directly exposed to toxic insecticide sprays in the field or exposure may come from honeybees collecting and bringing pesticide-contaminated pollen and nectar back to their hives to feed larvae and young bees. The presence of insecticides, along with other environmental stressors in agricultural areas, can be a factor leading to issues like colony loss — something beekeepers from around the world are trying to overcome.

    “Previous research has shown how chemicals like pesticides make bees more susceptible to mites,” said Yu-Cheng Zhu, a research entomologist at ARS’s Pollinator Health in Southern Crop Ecosystems Research Unit in Stoneville, Mississippi. “In our study, we wanted to see if mites and viral infestations make bees more susceptible to insecticides.”

    In a study, researchers with the U.S. Department of Agriculture (USDA)’s Agricultural Research Service (ARS) applied the miticide amitraz (Apivar), a product commonly used for treating Varroa mites, off-label to four bee hives and left the other four hives untreated. They monitored the mite population density monthly and DWV density in early, middle, and late season.

    Researchers collected bees from miticide-treated and untreated hives, and quantified gene expressions of four immune genes and two physiology-related genes. They also tested bees’ sensitivity to five representative insecticides. In addition, bees’ natural mortalities were recorded during three seasons.

    “Miticide treatment led to minor or undetectable mite and DWV infestations during the whole bee season, while untreated colonies had substantially higher mite and DWV infestations,” said Zhu.

    The data analyses showed that Varroa mite population irregularly fluctuated over the bee season and mite population density was not dynamically or closely correlated with the seasonal shift of honey bee natural mortality. Unlike mites, DWV density in untreated colonies progressively increased over the bee season. The density was highly correlated with the seasonal increase in honey bee natural mortality.

    “In the untreated hives, the increased DWV infestations resulted in decreased physiological and immunity-related functions in late-season honey bees, making the bees more susceptible to insecticides and increasing natural morality rates during the season,” said Zhu.

    According to Zhu, Varroa mites, also known as Varroa destructor, can reduce fat body and body fluids that contain important detoxification enzymes and immune proteins in honey bees. As a result, bees have impaired immune, detoxification/defense systems, and other essential processes. Coupling those impairments with exposure to insecticides can be detrimental to bee populations.

    “Having impaired immunity, especially later in the season with fewer food sources, can be challenging for honey bees,” said Zhu.

    Zhu, whose work focuses on the toxicological impact of pesticides on beneficial insects in the Mississippi Delta Area, said that the study’s results indicated the importance of studying the “bottom-up” effects of mite infestations on the overall health of honey bees in real-world contexts.

    “Chemical control is still a major method in preventing crop loss and controlling insect pest populations,” said Zhu. “It is important to study the effects of chemical control in honey bee populations so we can find best practices for protecting the health of bees.”

    The Agricultural Research Service is the U.S. Department of Agriculture’s chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in U.S. agricultural research results in $20 of economic impact.

  • Almond Board Launches New Website to Help Growers Coordinate NOW Mating Disruption Efforts

    In effort to improve area-wide management of navel orangeworm, the number one pest of the California tree nut industry, the Almond Board of California has launched a new website to help growers and PCAs coordinate/collaborate on mating disruption efforts. Funded by a grant from the California DPR, the Almond Board has created this new online tool with support from Land IQ, Blue Diamond Growers, and the UC Cooperative Extension.  Watch this video interview with Jesse Roseman and read more about it in Pacific Nut Producer Magazine.

    Please thank this video’s sponsor Suterra for their industry support.

  • Applying Herbicides Safely to Keep Residue Off of Harvested Almonds

    While there has been research and work underway to move the almond industry to off-ground harvesting such as is done in pistachios, harvested almonds currently spend just enough time in the dust of orchard floors that they can pick up trace residues of herbicides.  Watch this brief interview with UC Cooperative Extension Weed Specialist Brad Hanson as he shares how growers can mitigate this risk with more effective weed management planning and timing of herbicide sprays.

    Please thank this video’s sponsor Suterra for their industry support.

  • How Late is Too Late for Winter NOW Orchard Sanitation?

    The removal of nuts remaining on almond trees from the prior year’s crop is an important winter sanitation practice for the management of navel orangeworm (NOW), Amyelois transitella. Residual nuts are called ‘mummies’ and the process of removing the mummies is referred to as a ‘mummy shake’ because they are mechanically shaken from trees. This practice is conducted during the dormant and delayed dormant season, a time when orchard access may be thwarted by the winter rains.

    Most growers strive to have the mummy shake complete by mid-January when buds are dormant and less likely to abscise from the vibration caused by a mechanical shaker. As the flower buds progress toward bloom, they become more sensitive to the shaker vibration and more likely to abscise. Studies conducted in the 1980s (Sibbett et al.) established that the shaking of mummies by January 31 (approximately 8 days prior to bloom) at a Kern County site did not adversely affect yield; however, the authors cautioned growers of the risk of delaying mummy shakes further, particularly on early blooming varieties and in locations in the southern San Joaquin Valley. Because bud development and bloom date advance with increasing latitude, the potential risk of early and mid-February mummy shakes was investigated by W. Asai (Pomology Consulting, Turlock, CA) in the northern San Joaquin Valley. This work, conducted at a more northern latitude, suggested shakes conducted in early February may not compromise yield.

    The lack of yield detriment attributed to a mummy shake-mediated bud loss may seem counterintuitive; however, simple concepts of tree physiology may help explain this phenomenon. Consider that only approximately 30% of the flowers on a tree set a crop. A given tree does not have the carbohydrate stores needed to set every flower. As a result, the loss of a subset of flower buds may have little effect on overall yield. Naturally, the risk of crop loss increases the closer the shake approaches bloom, and both research groups suggested that mummy shakes be complete prior to the pink bud stage of development.

    Although rainy years make it difficult for growers to access orchards and complete orchard sanitation tasks, the heightened soil moisture adversely affects NOW survival in comparison to dry winters. Mummy nuts on the ground support enhanced NOW survival on a dry orchard floor than on moist soil with winter vegetation in the row middles. The next step in managing overwintering populations of NOW is destruction of mummies by flailing or mowing. Flailing and mowing should be completed by March 1, prior to the emergence of NOW. The emergence profile of NOW varies by location, but the first flight generally starts in late March.

    Growers who have not completed their winter sanitation practices by the end of January should walk their orchards to assess bud development in consideration of a delayed mummy shake. Winter sanitation can reduce now damage by up to 80%, so an early February shake may be worth the effort if orchard access is possible and bud development has not advanced into pink tip. For more information on NOW management, visit www.ipm.ucdavis.edu. — By Cameron Zuber & Elizabeth Fichtner, UCANR