California Ag Network

Category: Pest/Disease Management

  • Surveying Citrus Greening Risks in Southern California

    A screenshot of the risk-based survey for detecting huanglongbing (HLB) in Southern California. Colors represent the probability of HLB establishment or development, ranging from low risk (blue, near 0.0) to high risk (red, near 1.0). (Image provided by Weiqi Luo, North Carolina State University)

    Huanglongbing (HLB), also known as citrus greening, is the most devasting disease of citrus worldwide and has cost billions of dollars in economic losses. HLB has severely affected the citrus industry in Florida before any remedial action could be taken by growers. In California, HLB has been reported in urban backyard citrus trees that are a potential source of the pathogen. These infected backyard citrus trees threaten surrounding commercial citrus groves.

    ARS researchers in Fort Pierce, FL, and their research partners developed a refined risk-based survey (RBS) to help stakeholders survey for HLB in complex urban and suburban landscapes in Southern California. The RBS is being used by the citrus stakeholders and plant health regulators to identify and remove infected trees, which will help preserve the health of nearby citrus groves. Use of the model optimizes survey efforts and allocation of resources to combat HLB. The RBS is also updated with new detection data and refined continuously to better guide surveillance of HLB in Southern California. An online interface makes the most recent survey available to stakeholders.

  • Fusarium Wilt in Lettuce

    A new strain of fusarium wilt has been detected in lettuce, putting crops in danger. Researchers at UC Riverside are exploring new ways to combat this potentially devastating fungal disease. Alexander Putman spoke at the World Ag Expo in Tulare and with Matthew Malcolm from Malcolm Media Ag Publishing to discuss the issue. Watch this quick video and learn more in California Fruit & Vegetable Magazine.

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

  • Using Predators to Counter Asian Citrus Psyllids

    The Asian citrus psyllid is an active threat for growers and the main vector for Huanglongbing disease. These invasive insects have wreaked havoc in Florida and spread to Southern California, but researchers at UC Riverside are finding ways to counter them. Matthew Malcolm from Malcolm Media Ag Publishing interviewed Bodil Cass at the World Ag Expo to discuss the use of predators against psyllids. Watch this quick video and read more in California Fruit & Vegetable Magazine.

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

  • Fungicide Drenching to Combat Hazelnut Blight

    Eastern filbert blight is an ongoing and costly problem for hazelnut growers, but researchers at the Oregon State Extension are researching newer and more efficient ways to combat it. At the Nut Growers Society’s Winter Meeting, Jay Pscheidt spoke with Matthew Malcolm at Malcolm Media Ag Publishing and shared their findings on drenching. Watch this quick video and read more in Pacific Nut Producer Magazine.

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

  • Preventing Bacterial Blast Damage in 2026

    Though our weather outlook for the next couple of months is leaning toward warmer weather than usual, a cold snap during bloom and leaf-out could cause significant bacterial blast damage. Make a plan now in case of bad weather.

    The Bottom Line:

    • Bacterial blast can be a problem when cold, wet weather coincides with bloom or leaf-out.
    • Copper resistance is common: spraying copper is ineffective for preventing blast.
    • Frost protection is the most economical prevention option and will help prevent damage from both frost and bacterial blast.
    • The antibiotic kasugamycin (Kasumin®) is effective for preventing blast when applied up to 6 days before cold, wet weather. It is available this year under Section 18 exemption (Feb 1- April 15), consult with your PCA regarding rates and timings.

    The Details:

    Pseudomonas syringae can infect all aboveground parts of an almond tree, causing bacterial blast of the leaves and flowers. Pseudomonas is everywhere, so weather conditions are the factor driving this disease. Freezing cold, wet weather favors this disease. Pseudomonas is spread by water hitting the tree. If this occurs during frost, Pseudomonas can enter the tree through cells broken by frost damage. Trees are especially susceptible to frost damage during bloom and leaf-out, when tender new growth is exposed to cold weather.

    Preventing infection by Pseudomonas is the only way to control bacterial blast. Frost protection is the most inexpensive strategy: if the trees are not damaged by frost, Pseudomonas will not have a way in to cause disease. As a second line of defense, kasugamycin (Kasumin®) is effective to prevent bacterial blast when applied no more than 6 days before cold, wet weather. For this spray, complete coverage is crucial: all the tender new growth must be covered in a protective layer of the antibiotic for it to be effective. Any tissue left uncovered will be unprotected. Kasugamycin recently received a Section 18 for use in almond between February 1 and April 15, 2026. If the weather warrants treatment, kasugamycin can be used as a preventative spray up to two times during the temporary use window. Current work by UC researchers shows that copper-resistance is common in Pseudomonasthroughout the state. In some cases, mixing mancozeb with the copper may provide some level of control, but research shows that this mixt ure is not as effective as kasugamycin and can cause phytotoxicity.

    For more information on bacterial blast, check out these articles at www.sacvalleyorchards.com

    Bacterial blast/canker: What do we know?

    Bacterial Blast and Canker

    — By Jaime Ott, UC Extension Tehama, Shasta, Glenn and Butte Counties

  • USDA Shifts Fly Dispersal Efforts to U.S. Border

    The United States Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) is announcing a shift in its 100 million per week sterile fly dispersal efforts to stop the northern spread of New World screwworm (NWS). USDA will reallocate aircraft and sterile insects to reinforce coverage along the U.S.-Mexico border. The new dispersal area, or polygon, will include operations about 50 miles into Texas, along the U.S. border with the state of Tamaulipas, Mexico. Mass production and targeted dispersal of sterile insects are critical components of an effective strategy to fight NWS. Other tools including import protocols and surveillance continue to support these robust efforts to keep NWS out of the United States.

    “At Secretary Rollins’ direction, our highest priority is protecting the United States from screwworm,” said Dudley Hoskins, Under Secretary of Marketing and Regulatory Programs for USDA. “The northernmost active case of NWS in Mexico is still about 200 miles away from the border, but we’ve seen cases continue to spread in Tamaulipas and further south in Mexico, so we are proactively shifting our polygon as we make every effort to prevent NWS from reaching our border.”

    Sterile Fly Dispersal

    Sterile insect technique, when paired with surveillance, movement restrictions, and education and outreach, is an effective tool for controlling and eradicating New World screwworm. Female New World screwworm flies only mate once in their lives, so if they mate with a sterile male, they lay unfertilized eggs that don’t hatch. Releasing sterile flies just outside of affected areas helps ensure flies traveling to new areas will only encounter sterile mates and will not be able to reproduce. In this instance, USDA will release sterile flies north of the current active NWS cases in Mexico in a proactive effort to create a sterile reproduction buffer zone if the fly moves north from Mexico.

    Because it is important to continue ongoing surveillance efforts while releasing sterile insects, it is possible that sterile NWS flies could be caught and/or reported within Texas. To ensure officials can tell the difference between sterile and wild NWS flies, USDA will dye the sterile pupae, and the dye will transfer to the sterile flies when they hatch. The fluorescent dye will glow under UV light and may also be visible to the naked eye. If a sterile fly is captured in a trap, this dye will allow animal health officials to quickly rule the fly out as a threat.

    USDA will continue to deploy its intensive NWS response efforts including implementing import protocols, ongoing surveillance and trapping efforts along the border, investing in NWS innovation, and supporting robust response activities in Mexico and Central America.

    Import Requirements and Protocols

    Sterile insects are an important tool, but USDA’s import requirements and protocols add another line of defense for NWS and other foreign animal diseases that threaten U.S. livestock. Earlier this week, the importance of those protocols was highlighted when a horse from Argentina was presented for routine importation at an equine import quarantine facility in Florida. Upon examination, APHIS identified an open wound with larvae on the animal and promptly collected and shipped samples to the National Veterinary Services Laboratories (NVSL) in Iowa. The horse was immediately treated with medication to kill any larvae in accordance with standard, long-standing import protocols. This morning, NVSL confirmed that the larvae were New World screwworm larvae. Accordingly, the animal will remain in quarantine until it has been reexamined and determined to be free of NWS.

    This is an example of these long-standing import protocols working as designed. While this situation does not appear to be associated with the NWS outbreak in Mexico that USDA is currently fighting, it underscores the need for vigilance in all of USDA’s coordinated efforts to fight NWS.

    Surveillance, Monitoring, and Reporting

    USDA continues to lead intensive surveillance and monitoring systems along the U.S. border. Teams continue to check 121 NWS-specific traps across high-risk areas of border states and leverage thousands of fruit fly/insect traps aligned all along the Southern border. To date, more than 42,000 flies from traps in all locations have been submitted to APHIS NVSL for identification, with no NWS detections to date. APHIS Wildlife Services is also leading a coordinated effort to inspect wildlife for signs of NWS infestation. To date, they’ve inspected more than 9,300 wild animals across 39 different species and 131 U.S. counties and found no signs of NWS infestations.

    Even though there has been no detection of NWS inside the U.S. and the northernmost active case of NWS is still about 200 miles away from the border, USDA is asking U.S. animal owners to continue to remain vigilant by checking their pets and livestock for signs of NWS and immediately reporting anything suspicious to their state animal health officials or USDA area veterinarian in charge. Signs of NWS infestation include draining or enlarging wounds and signs of discomfort. Also look for screwworm larvae (maggots) and eggs in or around body openings, such as the nose, ears, and genitalia or the navel of newborn animals.

    Adult screwworm flies are about the size of a common housefly or slightly larger, with a metallic green or blue body, orange eyes, and three dark stripes down its back. NWS maggots can infest livestock and other warm-blooded animals, including people. They most often enter an animal through an open wound and feed on the animal’s living flesh.

    While NWS is not common in people, if you notice a suspicious lesion on your body or suspect you may have contracted screwworm, seek immediate medical attention.

    For more information on NWS and USDA’s efforts, visit Screwworm.gov. — USDA Animal and Plant Health Inspection Service

  • APHIS Expands Mediterranean Fruit Fly Quarantine in California

    The Animal and Plant Health Inspection Service (APHIS) expanded the Santa Clara Mediterranean fruit fly (Ceratitis capitata; Medfly) quarantine in Alameda and Santa Clara Counties, California. This action parallels the California Department of Food and Agriculture (CDFA) expansion of the Santa Clara Medfly quarantine published on January 2.

    APHIS and CDFA expanded the Santa Clara Medfly quarantine following the confirmed detection on December 17 of one wild male Medfly from a trap in on a residential property in an orange tree in Milpitas, Santa Clara County. This action expanded the quarantine by 17 square miles and does not include additional commercial agriculture. The amended quarantine encompasses 241 square miles with 58.76 acres of commercial agriculture, including grape, olive, orange, pepper, stone fruit, and tomato.

    APHIS is applying safeguarding measures and restrictions on the interstate movement of regulated articles to prevent the spread of Medfly to non-infested areas of the United States, as well as to prevent the entry of these fruit flies into foreign trade. APHIS is working with CDFA and the Agricultural Commissioners of Alameda and Santa Clara Counties to eradicate this transient fruit fly population following program guidelines for survey, treatment, and regulatory actions

    The APHIS Exotic Fruit Flies website contains descriptions and maps of all current Federal fruit fly quarantine areas. APHIS will publish a notice of this change in the Federal Register. —USDA Animal and Plant Health Inspection Service

  • Almond Conference Updates Growers on Best Practices for Bees & Pollination

    As almond growers prepare for pollinating their orchards — one of the most important tasks for establishing the new crop — here are insights from the Almond Conference to consider.  A “Honey Bees & Pollination” panel was moderated by Josette Lewis of the Almond Board of California (ABC).

    Hives Per Acre for Self-Fertile Cultivars: Elina Niño

    Following a string of bee losses over the past twenty years, 2025 was especially severe, with a 62% loss.  According to Elina Niño, apiculture scientist at UC Davis, the losses are becoming unsustainable.

    Niño pointed out that, in spite of having only 0.6 million of the 2.5-2.7 million colonies in the US, California ranks third in honey production, after North and South Dakota.

    Niño conducted a study of the pollination needs of self-fertile cultivars.  She excluded bees from some trees and for others used one or two hives per acre.  She counted the number of bees per flower per hour and after harvest she measured the kernel mass of 100 nuts per tree.

    The results showed that the number of visits per flower was similar for one hive as for two hives per acre.  Although the trees set more nuts and yielded more weight when one or two hives were present, kernel mass was higher where bees were excluded, presumably due to spreading the trees’ resources over fewer nuts.

    State of the US Commercial Beekeeping Industry: Matt Beekman

    The biological state of the beekeeping industry is precarious, according to Matt Beekman, a beekeeper based in Hughson, California who spends summers in North Dakota.  He presented a biological and financial State of the Beekeeping Industry report.

    Parasites & Pathogens: Varroa Mites & Viruses

    The varroa mite parasite continues to afflict beehives.  Reproducing quickly, the mites vector viruses that then spread from bee to bee in the densely populated hive.  The viruses can also spread in semen.  Area-wide applications of miticide help manage the mites.

    Only one chemical had been approved to suppress varroa mites since 2005.  That chemical, Amitraz, was registered for beehive use in 2013 in California, the last state to do so.  Some softer chemistries are available, but they are temperature dependent.

    California approved two new products in 2025, one oxalic acid-based and the other RNA-based.  They are expensive, though, costing $74 per colony per year.

    Nutrition: Where Have All the Flowers Gone?

    Each hive needs about 50 pounds of pollen and 100 pounds of nectar year.  With fewer acres enrolled in the federal Conservation Reserve Program, pollen and nectar may be scarce.

    Alternatively, almond growers can plant cover crops in the orchards to meet the need.  Seeds for Bees supplies free, appropriate cover crop seeds the first year and a discounted price the second year.  Many growers continue buying the seeds annually after seeing how effective they are.

    Pesticides: No to Organosilicon Adjuvant

    Used to amplify the effectiveness of pesticides, organosilicon surfactants harm bees.  Growers should ask their PCA to use one of the available alternatives instead.

    Beekman said that fungicides need to be sprayed during bloom, but advised using no tank mixes, adjuvants or insecticides during bloom, and applying fungicides in the early evening when bees are not flying.

    Financial Snapshot

    The net profit for beekeepers in 2024 was $11 per hive.  Overtime wages adversely impacted beekeepers, who need workers to do nighttime maintenance and overnight travel.  US honey production is declining due to fewer locations where bees can be placed to collect nectar.  The bees need more access to public land.

    Meanwhile, honey imports are increasing.  Imported honey is sometimes cut with synthetic sugar syrups.  Since honey is one of the few commodities for which the US does not have a standard definition, ambiguity and adulteration occur.

    India is now the largest exporter of honey into the US, with prices of $0.99-1.08/lb.   The US price is $2.69/lb., and the yield is declining.   

    Endangered Pollinator Species: Alexi Rodriguez

    Some insect species have been proposed for endangered species status for the first time, according to Alexi Rodriguez of the Almond Alliance.  One such insect is the monarch butterfly, which has little overlap with agriculture except for coastal sites in winter.

    A 2018 petition proposed adding four bumblebee species.

    Rodriguez said that if growers take reasonable, research-based steps to support pollinators, they will be immune to prosecution if incidental harm occurs.  The steps include using IPM (Integrated Pest Management) and planting pollinator habitat.

    Questions from the Audience

    Q: Is it worth getting mason bees to complement honeybees?

    A: Yes — blue orchard bees (a type of mason bee) — but you have to contract it separately.  They fly in colder temperatures and in rain.

    Q: Was there a bee shortage in 2025?

    A: That was not studied, but growers were saying that they did not get the number of frames they contracted for.  It’s possible that insufficient bees caused the lower yield last year, because everything else was good in 2025.

    Q: What about indoor cold storage of bees in empty warehouses to break the varroa mite cycle?

    A: It did not go well when tried in Kern County.

    Q: Does supplementing the almond orchard with pollen help with pollination?

    A: There is no research on that, but it is unlikely to help based on flower anatomy and the need for insects to get into the blooms to move pollen.

    Q: Does it help to move hives around during pollination?

    A: Yes, but it is a tradeoff economically due to the cost of labor to move the hives.  The most important variable is having morning sun on the hive to warm the bees enough to fly.  The bees will fly over the entire acre once they are warm.

    Q: What is a fair contract between grower and beekeeper?

    A: Eight frames average per hive; four to five frames minimum, 60% coverage.

    Q: Do herbicides impact bees?

    A: There is no research on that, but herbicides are not needed during bloom anyway.

    For more information about preparing for pollination, see Honeybee ABC.  – By Nancy Power, PhD, Assistant Editor, Pacific Nut Producer

  • Hazelnut Farmer Finds Clever Way to Handle Squirrel Trouble

    Squirrels can be a serious headache for nut growers, who often have to come up with their own ways of catching and getting rid of them as rodenticides are not always an option. Oregon hazelnut grower Ken Baker talks to Matthew Malcolm with Pacific Nut Producer about the way he has learned to trap squirrels at his farm. Watch this quick video and learn more in Pacific Nut Producer Magazine.
    Please thank this video’s sponsor George Packing Company for their industry support.

  • Almond Industry Requests EPA Follow Sound Science in Essential Product Registration

    The Almond Industry is seeking Section 18 emergency approval for the use of an essential bactericide for the sixth year. A product that has been fully registered in other commodities, Kasumin should be registered for use in almonds, but the EPA is ignoring the sound science showing that it’s safe and beneficial for almonds under critical weather conditions. Watch this brief interview as Jim Adaskaveg from UC Riverside explains with Matthew Malcolm on California Ag Network and read more in Pacific Nut Producer Magazine.