California Ag Network

Category: Pest/Disease Management

  • Widespread Rat Infestation in Orchards & Vineyards, CAPCA on Tools & Resources Moving Ahead

    As if California growers and PCAs didn’t have enough on their plates with rising input costs compounded by the most restrictive laws & regulations in the nation, they’ve been further challenged with an unusual pest problem this year — rats! An  increasing number of abandoned orchards and vineyards due to poor economic circumstances has caused a feeding frenzy for some uninvited rodent guests, whose numbers have been multiplying at unprecedented levels. Ruthann Anderson, President/CEO of the California Association of Pest Control Advisers (CAPCA), met with Matthew Malcolm on California Ag Network to explain this issue and what they are doing to help provide the tools and resources growers and PCAs to combat this emergency situation, beginning with an anonymous survey they can fill out HERE. Watch this brief video to learn more.

  • Kemin introduces RevoCURB™, a new safe and versatile soil treatment tool to address agricultural issues such as restrictions on fumigants and the requirements for buffer zones.

    SPONSORED CONTENT

    Fumigants are a cornerstone of conventional agriculture in the United States for combating soil-borne pests and diseases. However, fumigants also have significant limitations, including application requirements, buffer zone restrictions and the lack of available products for organic farmers.

    The role of fumigants in agriculture

    Fumigants are chemical agents applied before planting to eliminate pests, pathogens, and weeds, which protect crops and improve vigor and yields, especially in high-value crops like strawberries and tomatoes. Despite their effectiveness, most carry significant health and environmental risks, leading to strict regulations on their use, application timing, permitting, and buffer zones1,2. In some cases, these health concerns have led to complete bans on specific products, such as methyl bromide, which has been restricted in both the United States and Europe2,3.

    Buffer zone restrictions

    To reduce exposure risks, the Environmental Protection Agency (EPA) enforces strict buffer zones, areas where fumigant application is prohibited, near public spaces like schools and hospitals. Zone size depends on the fumigant used, application method, local environmental conditions, and distance to public spaces. While crucial for public safety and conservation efforts, buffer zones decrease usable farmland. Often, untreated buffer zones can lead to uneven pest control and reduced crop yields4. Buffer zones also add regulatory burdens, including signage and detailed management plans, increasing cost and complexity2.

    Additional limitations of fumigants

    Beyond buffer zone requirements, fumigants come with additional key limitations:

    • Cost: Fumigation is expensive, requiring investments in chemicals, labor, and regulatory compliance, which are often unaffordable for small-scale farmers.
    • Equipment: The application requires specialized equipment, including shank injectors, calibrated applicators, tarping systems, and enhanced personal protective equipment, which further increases total expenses.
    • Application Conditions: Efficacy depends on precise environmental conditions (soil temperature, soil moisture, weather) and properly calibrated equipment to ensure efficacy
    • Environmental Risks: Fumigants are highly volatile and can drift off-site, endangering nearby communities and ecosystems. Improper application may lead to water contamination or harm to non-target organisms.

    Organic alternatives to fumigants

    For organic farmers, the limitations of fumigants are even more pronounced, as organic certification prohibits the use of most synthetic fumigants. In response to these challenges, organic farmers rely on natural alternatives to manage soil-borne pests and diseases5:

    • Soil Solarization: Fallow fields are covered with plastic during peak heat for 4-8 weeks to trap solar energy, which can kill pathogens, pests, and weed seeds. This timeline may be challenging as the temperatures required for effective treatment coincide with peak growing seasons.
    • Anaerobic Soil Disinfestation (ASD)6: Organic materials like rice bran or mustard seed meal are incorporated into the soil and the soil is then saturated with water and covered with plastic to create anaerobic conditions. As oxygen is depleted, aerobic pests die and anaerobic species flourish, producing byproducts that further suppress pathogens. Once the field is cleared and prepared for planting, the reintroduction of oxygen into the soil then reduces anaerobic microbial populations, resulting in a cleaner overall soil. This process, however, can be quite expensive as it is water- and input-intensive and can be ineffective if fields are drained too early.
    • Crop Rotation and Cover Cropping: These practices disrupt pest life cycles and improve soil health; however, they are inadequate to knock down heavy infestations without additional inputs.
    • Biological Controls: Beneficial species help suppress pests via predation or competition. Their success depends on careful species selection, application timing, and environmental fit, and they work best when paired with other methods of control.

    Introducing RevoCURB™, a safe-to-use, 3-in-1 solution for organic and conventional growers.

    RevoCURB™ is a new OMRI-listed, 3-in-1 soil treatment designed to enhance crop health and yield by targeting plant parasitic nematodes, microbes, and pre-emergent weed seeds. Exempt under FIFRA 25(b), RevoCURB offers a 0-hour restricted entry interval (REI), no restrictions on maximum residue levels, minimal requirements for personal protective equipment, and no need for buffer zones. RevoCURB utilizes the power of Smart Blend Technology and four essential oils – thyme, clove, garlic, and cinnamon to provide control through multiple complementary modes of action. These oils disrupt cellular membranes on contact, inhibit nematode egg hatching, impact the nervous systems of juvenile nematodes present in the soil, causing paralysis and death, vaporize within the soil column, repelling pests and delaying repopulation and suppress weed seed germination.

    “These contact and repellency modes of action work in tandem upon application of RevoCURB to disrupt pest lifecycles and prepare soils for planting.” – Emma Trainer, Scientist at Kemin Crop Technologies.

    RevoCURB should be applied 14 days prior to planting or post-harvest and watered in per label directions to maximize efficacy and the zone of protection without harming crop seeds, seedlings, and plugs.

    Field trial to assess the effectiveness of RevoCURB on root-knot and stunt nematode populations on cucumber. San Luis Obispo, California (Credit: Bradley Booker at Pacific Ag Research) (SD-25-28093)

    RevoCURB protects young crops from multiple soil pest pressures, allowing for healthier plants and greater yields. Because it’s free from buffer zone requirements, REI, and residue restrictions, RevoCURB is ideal for transitional areas and organic acreages – bringing flexibility and safety where conventional fumigants fall short.

    For more information about RevoCURB, visit www.kemin.com/revocurb or contact us croptech@kemin.com

    References

    1. Panth, M. & Hassler, S. and F. Baysal Gurel (2020). Methods for Management of Soil-borne Diseases in Crop Production. Agriculture,
    2. United States Environmental Protection Agency. Soil Fumigant Toolbox. https://www.epa.gov/soil-fumigants
    3. European Commission. European Community Management Strategy for the phase-our of the critical uses of methyl bromide. April 2009. https://ozone.unep.org/sites/default/files/additional-reported-information/MeBr_Submissions/EC%20Management%20Strategy%20for%20Methyl%20Bromide.pdf
    4. Vansickle, J.J.; Smith, S.; and R. Weldon (2009). Impacts of EPA proposed buffer-zone restrictions on profitability of Florida strawberry growers. University of Florida Institute of Food and Agricultural Sciences; FE795.
    5. Bolda, M.P.; Dara, D.K.; Daugovish, O.; Koike, S.T.; Ploeg A.T.; Brown, G.T.; Fennimore, S.A.; Gordon, T.R.; Joseph, S.V.; Westerdahl, B.B.; and F.G. Zalom. Non-fumigant alternatives for soil disinfection. UC IPM Pest Management Guidelines: Strawberry. UC ANR Publication 3468. University of California Agriculture and Natural Resources, Davis, CA. https://ipm.ucanr.edu/agriculture/strawberry/non-fumigant-alternatives-for-soil-disinfestation/#gsc.tab=0
    6. Lopes, E.A.; Canedo, E.J.; Gomes, V.A.; Vieira, B.S.; Parreira, D.F.; and W.S. Neves (2022). Anaerobic soil disinfection for the management of soil-borne pathogens: a review. Applied Soil Ecology, 174.

    © Kemin Industries, Inc. and its group of companies 2025. All rights reserved. ® ™ Trademarks of Kemin Industries, Inc., USA. Always read and follow label directions. FIFRA 25(b) Exempt: RevoCURB has not been registered by the United States Environmental Protection Agency. Kemin Industries, Inc. represents that this product qualifies for exemption from registration under the Federal Insecticide, Fungicide, and Rodenticide Act. The products are not registered or authorized for sale in all states. Consult with your Kemin representative or state regulatory representative for approval of this use in your state, specific applications, and labeling. croptech@kemin.com | 800-752-2864 (ext.2).

  • California Orchards Blossom with NRCS Help Managing Pests

    California’s Central Valley is a land of agricultural abundance, known for its incredible diversity of crops including fruits, vegetables and nuts. It produces approximately 25% of the nation’s food.

    But with plenty can come pests – in as many varieties and types as the crops grown in the region. Area farmers have worked with USDA’s Natural Resources Conservation Service (NRCS) to implement integrated pest management into their orchard operations with marked results.

    Sandra and Mike Smith of Smith Family Farm in Fresno, California, showed NRCS Chief Aubrey Bettencourt the benefits of the practices that they have incorporated with NRCS assistance as they toured their 36-acre almond orchard.

    Established in 1903, the farm is on the cusp of welcoming its fifth generation of farmers. By adapting their operations to increase conservation and sustainability practices, the Smiths hope to pass on a rich legacy to their young granddaughters.

    The Smiths highlighted the impact that integrated pest management practices – notably hormone disruptors – have had in their fight to combat navel orangeworms in their almond orchards.

    “We were at 17.1% loss of our almond crop two years ago because of the infestation of navel orangeworms,” Mike Smith told Chief Bettencourt. “Once we implemented the mating disrupters, we were able to bring our almond reject numbers down to 1.1%.”

    Navel orangeworms burrow into almond nuts to feed on the kernel, damaging the nut and impacting producers’ overall yield and harvest quality. Deploying pheromone-based mating disruption tools can reduce navel orangeworm populations by hindering male moths’ ability to locate females.

    The Smiths have also leaned on NRCS technical assistance to implement other conservation techniques to increase the health of their orchard. The family now prioritizes composting and increasing organic matter, guided by the knowledge gained through NRCS collaboration.

    Further north, Chinchiolo Farming Co., Inc., a family-run business located in Lodi, California, is managing orchards of a different kind while embracing similar production practices.

    Producer James Patrick Chinchiolo has worked to uphold a century-old farming legacy, started by great grandfather Italian immigrant James Joseph Chinchiolo. Chinchiolo has worked with NRCS to incorporate a number of conservation practices including cover crops, tractor replacements, orchard removal and soil incorporation.

    Like the Smiths, Chinchiolo has dealt with pest issues, incorporating a Biologically Integrated Orchard Systems (BIOS) approach in managing his orchards. The BIOS system aligns with NRCS principles, embracing the implementation of conservation practices like cover cropping, beneficial insect habitat, and compost application to keep pests at bay.

    “We aim to foster a more ecologically balanced environment within our orchards,” Chinchiolo said during his discussion with Chief Bettencourt. “We are focusing on minimizing our inputs and creating more habitat for beneficial insects to flourish to help control unwanted pests.”

    Conservation practices like cover cropping and compost application not only help pollinators flourish – a crucial part of growing beautiful cherries – they also protect the trees’ overall health, improving soil structure and water retention.

    After last summer’s heat impacted this year’s cherry crop, Chinchiolo is working to take additional measures to make his trees more heat resistant in preparation for next season.

    “Growing cherries is never predictable. But it’s always beautiful.” Chinchiolo said.

    Helping People Help the Land

    During her visit, Chief Bettencourt emphasized that the agency’s primary focus is to give producers the tools that they need to be the best producers that they can be – increasing their yield while stewarding the nation’s natural resources.

    “Producers are the solution, and we want to empower them by getting our highly skilled staff out in the field to provide technical support. We want to streamline our programs to work better and faster for producers,” she said.

    NRCS helps farmers, ranchers and forest landowners make critical investments in their operations and local communities by helping them implement proven practices to ensure all of America’s farms, ranches and private lands are economically viable and thriving.

    If you are interested learning how these programs can help you achieve your operational and land management goals, find your local USDA Service Center and get started today.

    Follow the Chief through our blog series as she meets with producers across the country to learn how NRCS has helped their operations. — By Debra Denhart, Public Affairs Specialist, USDA

  • Medfly Quarantine in Portion of Santa Clara County

    A portion of Santa Clara County has been placed under quarantine for the Mediterranean fruit fly (Medfly) following the detection of two wild female flies in the city of San José. If not stopped, Medflies can devastate fruits and vegetables grown in backyards and on local farms by reproducing and leaving larvae in produce, and the invasive flies can then spread to other regions. A quarantine is a way to minimize damage and stop the risk of spread by restricting the movement of fruits and vegetables.

      

    CDFA is working collaboratively with the United States Department of Agriculture (USDA) and the Santa Clara County Division of Agriculture on this project.  This project is new and separate from the recently-eradicated Medfly infestation in Alameda County.

     

    The quarantine area measures approximately 109 square miles, bordered on the north by Trade Zone Boulevard; on the south by Camden Avenue; on the west by San Tomas Expressway; and on the east by Evergreen Valley Community College.  The quarantine will cover parts of the cities of San José, Santa Clara, Campbell, and the town of Los Gatos. A link to the quarantine map may be found here: www.cdfa.ca.gov/plant/medfly/regulation.html

      

    The quarantine will affect any growers, wholesalers, and retailers of susceptible fruit in the area as well as local residents.  Home gardeners are urged to not move homegrown produce from their property.  However, residents living in the quarantine area may consume or process (i.e. juice, cook, or grind in the garbage disposal) fruit on the property where they were picked or dispose of fruit by bagging and sealing and placing in the garbage (not green waste).  These actions protect against the artificial spread of the infestation to nearby regions where it can affect California’s food supply and backyard gardens.

      

    Sterile male Medflies are scheduled to be released in the area as part of the eradication effort. The release rate will be 250,000 males per square mile per week in an 84.76 square mile area around the infestation.  The sterile medfly release program has a proven track record of eradication in California.  Sterile male flies mate with fertile wild female flies in the natural environment but produce no offspring.  The fly population decreases as the wild flies reach the end of their natural life span with no offspring to replace them, ultimately resulting in the eradication of the pest.  The sterile male medflies are reared at the joint CDFA/USDA sterile insect rearing facility in Los Alamitos, California, which prepares sterile flies for release everyday over California.

      

    Additionally, properties within 200 meters of the detection sites are treated with an organic formulation of Spinosad, which originates from naturally-occurring bacteria in soil, to eliminate any mated females and reduce the density of the population.  To further reduce the population, properties within 100 meters of infested properties are subject to host-plant or fruit removal to eliminate eggs and larvae.

      

    This eradication approach is the standard Medfly program used by CDFA and is the safest, most effective, and most efficient response program available.  CDFA has successfully eradicated each and every detected Medfly infestation in California history, dating back more than 40 years.

      

    The pest is known to target more than 250 types of fruits and vegetables. Damage occurs when the female lays eggs inside the fruit.  The eggs hatch into maggots, which tunnel through the flesh of the fruit, making it unfit for consumption.  Residents who believe their fruits and vegetables are infested with fruit fly larvae are encouraged to call the State’s toll-free Pest Hotline at 1-800-491-1899 or email reportapest@cdfa.ca.gov.

      

    While fruit flies and other invasive species that threaten California’s crops and natural environment are sometimes detected in agricultural areas, the vast majority are found in urban and suburban communities.  The most likely pathway for these invasive species to enter our state are by “hitchhiking” in fruits and vegetables brought back illegally by travelers as they return from infested regions of the world or from packages containing fruits and vegetable from other states or countries.  To help protect California’s agriculture and natural resources, CDFA urges travelers to follow the Don’t Pack a Pest program guidelines (www.dontpackapest.com/).

     

    To help prevent future introductions, residents are encouraged to:

    • Assist agriculture crews working to protect your garden by allowing them access to your yard to place traps and inspect plants.
    • When entering California from another state or country, avoid bringing agricultural products – including fruits and vegetables.  Help us protect our agriculture, natural resources, and California’s unique biodiversity from invasive fruit flies – please Don’t Pack a Pest (www.dontpackapest.com/).
    • Determine if your property is located within an active quarantine area by visiting www.CAFruitFly.com.
    • Please do not send or receive any homegrown fruit, vegetables, or meat products, as they may contain invasive species that can “hitchhike” in these products.
    • Inspect your garden regularly for signs of invasive fruit flies or maggots and report any findings to CDFA at 1-800-491-1899.

      

    Federal, State and County agricultural officials work year-round to prevent, deter, and eliminate the threat of invasive pests and diseases that can damage or destroy our agricultural products, natural environment, resources, and unique biodiversity.  The efforts are aimed at keeping California’s food supply plentiful, safe, and pest-free.

      

    Residents with questions about the project may call CDFA’s Pest Hotline at 1-800-491-1899.  To learn more about invasive species and how to protect California’s fruits and vegetables, please visit www.cdfa.ca.gov/plant/fruitfly

  • Confronting the Rodent Crisis: Challenges and Interventions for Almond Growers

    California almond growers are facing an unprecedented challenge this season as a severe roof rat infestation sweeps through orchards across the Southern and Western San Joaquin Valley. An early survey indicates the outbreak has impacted well over 100,000 acres, a number that has likely grown, causing widespread damage and significant economic losses.

    What the Almond Board of California Has Learned

    Almond growers across Merced, Fresno, Kings, and Kern counties have reported an alarming spike in rodent populations. Over the last several months, ABC has participated in tours and meetings about the severity of this rat infestation, and field observations indicate that these rodents are using irrigation canals and other waterways as corridors, enabling them to rapidly spread between orchards and diverse agricultural fields. This mobility is exacerbating the extent of damage and complicating containment efforts.

    Roof rats are arboreal, meaning they spend a considerable amount of their life above ground, often building nests in trees. However, for several years, researchers have noted that in almonds and other tree nuts, they use burrows extensively.  Although it’s undetermined as to why, some believe it’s the lack of cover in the winter months that drives this behavior.

    According to preliminary findings from a CDFA-led surveyconducted in the fall of 2024, monitoring efforts revealed particularly high densities of rats in the reported areas, with up to 32 rats captured per night at some locations. Direct damage to the trees occurs through consumption of nuts, girdling of small and large limbs, and burrowing in the root zone. Additionally, damage to irrigation systems, equipment and other infrastructure within orchards is often greater than direct crop loss.

    Economic analyses from the CDFA report estimated total on-farm losses ranging from $109 million to $311 million. Major expenses contributing to these figures included drip line replacements, which alone accounted for losses between $56 million and $168 million, and yield losses resulting from disrupted post-harvest irrigation, estimated at $43 million to $129 million. Additional significant costs stemmed from direct tree damage, farm equipment repairs, machinery cleaning due to rodent contamination and replacement of damaged trees.

    The lower-end estimates assumed less extensive damage, such as 25% of affected acreage needing drip line replacement and 10% tree damage. Conversely, the higher-end scenario accounted for more severe conditions, including drip line replacements on 75% of impacted acreage, 15% tree damage, and substantial farm equipment repairs and maintenance.

    Photo Caption: Irrigation line damage from rats

    Drip line damage and yield reductions alone represented nearly 90% of the anticipated financial impact. Furthermore, CDFA cautions that these numbers may underestimate the true financial burden, as broader impacts, including newly planted orchards and extensive post-harvest cleanup beyond farm machinery, were not fully quantified in the preliminary analysis.

    During ABC’s learnings, one grower noted the replacement of an entire drip irrigation system was estimated at $20,000, and the rodents also chewed through irrigation wiring causing fires. A second almond grower detailed extreme damage that was estimated at a 50% crop loss, even while he was exterminating between 50-100 rats a day.

    Photo Caption: Aside from equipment and tree damage, rats are eating the nuts themselves on the tree.

    UC ANR’s IPM Recommendations

    Farm managers, PCAs, and growers are expressing growing frustration and concern over their ability to sustain operations. Management strategies currently in use include bait stations and aluminum phosphide treatments of burrows in the winter, and less conventional methods such as snap traps, owl boxes and applying carbon monoxide or carbon dioxide into burrows as another fumigation option. However, many growers report these tactics are labor-intensive, costly, and insufficient for the scale of this infestation. Additionally, growers noted that rotating bait flavors has become necessary as rodents quickly grow wary and “bait shy.”

    Based on research led by UC ANR scientists Niamh Quinn and Roger Baldwin, growers are advised to implement a comprehensive Integrated Pest Management (IPM) strategy tailored specifically to roof rat behavior in tree nut orchard environments. The cornerstone of effective IPM is rigorous monitoring with the use of tracking tunnels and ink cards. Strategically placed game cameras can pinpoint rat activity hotspots, while also providing information on how rat numbers are changing over time.

    Using that information, growers can then implement targeted baiting programs. Elevated bait stations containing diphacinone-treated oats, positioned every 165 feet, align with roof rats’ natural climbing behavior while minimizing risks to non-target species. For tree nuts, bait stations strategically placed on the ground could also help, although this application is limited to dormant seasons. To have a significant impact, growers must keep stations full of fresh bait over a period of about four weeks. In situations where rat densities are very high, a longer period may be needed.

    Again, monitoring is important during the bait program period and growers should stop the program when bait consumption becomes minimal. As a reminder, rodenticide regulations are ever-changing, and applicators should always read the label carefully to ensure compliance.

    Strategically placed snap traps in protective trapping tunnels, spaced approximately 245 feet apart, form a crucial component of long-term rat control post-baiting. Regular maintenance and monitoring of these traps are necessary to sustain effectiveness. Collaboration among neighboring orchards can further enhance the efficacy of these integrated pest management measures.

    During the dormant season, broadcasting zinc phosphide bait or applying zinc phosphide within burrows is also an option, although the efficacy of this bait for rats in California orchards is unknown. Burrow fumigation with aluminum phosphide, gas cartridges or carbon monoxide and carbon dioxide injection devices are also options. UC ANR advises growers to be aware that if using aluminum phosphide, in addition to normal requirements that apply to all restricted-use fumigants, you also now need to have a Burrowing Vertebrate Pest Fumigation Certificate (PCA license) to use this product.  Also note that any diphacinone-treated bait for use in bait stations must be bought from a County Ag Commissioner’s office.

    Based on the level of infestation learned from using the tracking tools, multiple overlapping strategies may be necessary to reduce the populations.  And if possible, rotating to a non-diphacinone option is a good decision to avoid diphacinone-resistance.

    Additional Support and Resources on the Horizon

    Industry groups are mobilizing to provide tangible support for growers facing ongoing rodent pressures. CAPCA, in collaboration with the Almond Board of California and other agricultural partners, is pooling funds to purchase and distribute abatement stations or owl boxes to affected regions, depending on CDFA recommendations.

    Additionally, CDFA is actively working to facilitate updates to pesticide labels for rodent control materials. Specifically, updates and approvals for the use of zinc phosphide and diphacinone are in progress, which could expand application options for growers if finalized. These advancements would provide growers with additional chemical tools to integrate into their rodent management programs.

    Furthermore, the latest information and assistance opportunities are being planned for informative sessions at the 51st Annual CAPCA Conference in October and The Almond Conference in December. UC Cooperative Extension’s Roger Baldwin will be presenting Monday, October 20, at the annual CAPCA conference in Reno, Nevada. ABC’s Gabriele Ludwig will be leading a discussion about rodent control in the face of changing regulations at The Almond Conference December 10-12 in Sacramento, CA. — By the Almond Board of California

  • Ants Protect Deadly Citrus Disease Vector – New Ant Management Tools

    Ants are known to interfere with biological control of key citrus pests because they feast upon the sugary honeydew produced by small insects. One of these key pests is the invasive asian citrus psyllid that vectors the deadly huanglongbing citrus disease. As California growers diligently work to keep this disease out of citrus orchards, effective ant management is a critical component in the game plan. Ivan Milosavljevic from the California Citrus Research Board met with Matthew Malcolm on California Ag Network to discuss some new game-changing control strategies. Watch this brief interview and read more about it in California Fruit & Vegetable Magazine.

  • Scouting for Vine Mealybug and Other Pests with American Vineyard Live

    Kent Daane, UC Cooperative Extension Entomology Specialist, and Jeannine Lowrimore of Pacific Bio Control join American Vineyard Live to discuss some of the best practices for control of Vine Mealybug and other vineyard pests this summer. Watch the one hour presentation now or listen at the links below.

    Special thanks to the title sponsor Pacific Bio Control.

    Watch our previous Presentation: What Weeds are Telling You About Your Soil Health with American Vineyard Live

  • California Dairies Still Struggling with Bird Flu – Why Isn’t it Going Away?

    CDFA’s most recent data show that of the roughly 770 California dairies that have been infected with Avian Influenza. Some 630, more than 80%, have been released from quarantine. Of the approximately 140 infected herds remaining, most are making steady progress towards quarantine release.

    For a small number of producers, however, the pathway back to normal has remained prolonged and frustrating. CDFA estimates some 10 to 15 herds have experienced unusually long quarantines, in one case over 10 months. These farms might achieve one or two negative weekly bulk tank tests, only to have a weak positive again, resetting the quarantine release clock. There are reports from dairies in other states experiencing similar problems.

    Just as frustrating for several California producers is to have been actually released from quarantine only to have a positive bulk tank some weeks or months later. These cases have been reported as typically involving a limited number of clinical cows, most often springing heifers.

    What’s causing persistent or reoccurring positive bulk tanks?

    CDFA’s Dr. Natalie Ward says it’s useful to remember that the PCR assay used for HPAI detection is extraordinarily sensitive. “Just one cow actively shedding virus can trip a bulk tank positive,” Ward says. What might be allowing the virus to remain circulating on some farms is an area of intense research. In California alone, some $2 million of state and federal research is currently being conducted. Investigations into potential causes of persistent or reoccurring positive bulk tanks include:

    Chronic Shedders?

    Dr. Jason Lombard of Colorado State’s vet school has directed some of the largest H5N1 dairy surveys in the country. He explains that one possible explanation could be non-clinical cows shedding for prolonged periods. “We’ve detected cows that were continuing to shed virus out to at least 90 days, long after they recovered clinically.” Dr. Lombard says. The role of persistent shedders remains speculative for now, however, at least until whole-herd surveys can be performed to identify potential chronically infected cows.

    Carried by Birds?

    Certainly, migratory waterfowl were determined to be the original source of Texas spillover event in 2024. Federal testing of birds in the vicinity of dairies however, has revealed that local, non-migratory birds, such as blackbirds, starlings, doves and pigeons have been positive for H5N1 genetic material. This raises the worrisome scenario that HPAI is circulating within local bird populations potentially shedding the virus into cows’ feed and water sources. Whether the virus is reproducing within these nuisance birds and being shed in numbers sufficient to infect cows remains unknown.

    Carried by Flies?

    Researchers with the USDA’s Agricultural Research Service (ARS) are collaborating with industry partners in California to survey both biting flies, such as Stable Flies, and non-biting flies, such as House Flies. The goal is to determine if these insects can carry the disease-causing virus and understand their potential role in transmitting the disease from cow-to-cow or from herd-to-herd.

    Carried by Dust?

    In yet another industry-academic collaboration, researchers from Emory University are collecting aerosol samples on quarantined California dairies from a variety of sites including in the parlor, pens and over lagoons. Air from these sites is run through filters to collect particulate matter which is assayed for the presence of both HPAI genetic material and intact, infectious virus.

    New Herd Additions?

    One more potential cause of persistent or reoccurring positive bulk tanks is newly purchased or returning cattle. Infected but non-clinical cattle, or youngstock returning from calf ranches, could be harboring the virus, serving as a new nidus of herd infection. Because much of the herd might be immune due to previous infection, the amount of clinical disease in the herd could remain limited. Alternatively, new or returning animals who have never experienced HPAI infection might be introduced to the virus which is persisting in low levels in the dairy environment. Such “immunologically naïve” animals, having no protective antibodies, could develop full-blown clinical disease and shed sufficient virus to trip a positive bulk tank test.

    Decaying Cow Immunity?

    Complicating producers’ biosecurity efforts is a lack of data on how long immunity persists following natural infection. This is true regardless of whether the virus is being re-introduced by outside sources (i.e. local birds, asymptomatic cattle) or is simply circulating at low levels within the herd. Following experimental infection protective antibodies have persisted for at least one month, but unpublished bulk tank studies suggest such protection might wane after 3 to 6 months.

    Guidance for producers?

    The research described above as well as other investigations will eventually describe how HPAI circulates among domestic animals and wildlife. Producers however understandably want to know what then can do now. State and federal animal health officials advise producers not become complacent about biosecurity once released from quarantine. CDQAP’s Bird Flu homepage contains a biosecurity section where the best references to help protect your herd have been collected. Ultimately HPAI cattle vaccines, which are in the final stages of approval, should provide producers permanent relief. — By Dr. Michael Payne, UC Davis, School of Vet. Medicine, Director, California Dairy Quality Assurance Program

  • Funding Available for California Citrus Growers to Fight Asian Citrus Psyllid, Prevent Citrus Disease

    Huanglongbing (HLB), the deadly citrus disease that decimated the Florida citrus industry has shown up in Southern California and is now threatening the nation’s number one citrus state.  HLB is primarily spread by the invasive Asian Citrus Psyllid, so managing this insect is key to preventing the spread of the disease. Pest mitigation practices may be costly, the California Citrus Research Board (CRB) introduced the California Citrus Research and Field Trials program (CA-CRaFT) to help fund commercial growers (both conventional and organic) to implement these practices. CRB representative Ivan Milosavljevic met with Matthew Malcolm on California Ag Network to share details. Watch this brief interview and read more in California Fruit & Vegetable Magazine.

  • California DPR Proposes Regs for Tracking Reportable Pesticide Use Near Schools

    The California Department of Pesticide Regulation (DPR) released proposed regulations to implement Assembly Bill (AB) 1864, signed by Governor Newsom on September 25, 2024, to require field identification and reporting on pesticide use near schools to provide greater transparency and ensure compliance with existing regulations that restrict agricultural pesticide use near schools and licensed child day care facilities.

    Effective Jan. 1, 2018, DPR adopted regulations to place restrictions on the application methods or timing used to apply pesticides to agricultural fields within 1/4 mile of a schoolsite, currently defined as a public K-12 school or licensed child day care facility. The regulations also require the operator of the agricultural field within 1/4 mile of a schoolsite to provide the schoolsite an annual notification of expected pesticide applications.

    The proposed regulations would require:

    •A separate site identification number for the portion of an agricultural field that lies within 1/4 mile of a schoolsite

    •Restricted material permit applications, notices of intent, and pesticide use reports for agricultural fields within 1/4 mile of a schoolsite to include the specific method of applying the pesticide

    •Notices of intent submitted for the use of California restricted materials on agricultural fields within 1/4 mile of a schoolsite to include allowable dates and time ranges during which the application can occur

    Additionally, the proposed regulations will expand existing restrictions to include private K-12 schools with an enrollment of 6 or more pupils.

    DPR has opened a public comment period on the proposed regulations through July 14, 2025. Comments may be submitted online through DPR’s public comment portal SmartComment, sent by email to regulations@cdpr.ca.gov, or by mail to:

    Lauren Otani, Regulations Coordinator

    Department of Pesticide Regulation

    1001 I Street, P.O. Box 4015

    Sacramento, California 95812-4015

    The proposed regulations and rulemaking documents are now available at DPR’s Proposed and Recently Adopted Regulation webpage.