Pacific Nut Producer Magazine

Category: Pest/Disease Management

  • Almond Market Looks Strong Going Into 2027

    The almond industry is entering the new crop year from a solid position according to a recent market update from Blue Diamond Growers. This is thanks in no small part to exports to India.

    The 470.7-million-pound carry-in (of which only 447.1 million pounds is estimated as edible) is down from prior year and confirms the tightness in supply from one crop to the next. Downward pressure on crop potential and overall supply and demand fundamentals continue to support a stable-to-firm market outlook. Export demand remains healthy with the coming weeks expected to provide clarity on crop size, kernel sizing, and the degree to which rapidly appreciated pricing can be absorbed by end markets.

    The 2026 crop year started on a positive note, meeting strong industry expectations. August shipments totaled 190 million pounds. Exports reached 143.2 million pounds, an increase of 31%, while the domestic market shipped 46.8 million pounds at a modest -3.3% decrease versus last year. With six of the last seven last months’ total shipments outpacing previous year, the industry continues to experience strength in global demand.

    India was the clear standout in August, receiving 44.3 million pounds, up approximately 170% from 16.4 million pounds last year. The increase reflects stronger replenishment ahead of the festival season and a normalization from the unusually low August 2025 shipment level. The magnitude of the increase is notable given elevated pricing and confirms India’s continued importance as the primary outlet for California inshell almonds. Local consumption will become increasingly important ahead of festival season as buyers will begin to replenish stocks that dwindled at the end of the 2025 crop year.

    August domestic shipments totaled 46.8 million pounds, down 3.3% year over year. While this may not have been the start to the year the industry had hoped for, the improvement in shipment performance over the last six months provides optimism that the market has stabilized. As prices rose over the last month, purchasing activity slowed and shifted to closer, strategic locations. This cautious approach is expected to continue. Looking ahead, domestic demand is expected to remain steady, with a pipeline of commitments providing support for shipments in the next few months.

    The 2026 crop is progressing rapidly with current receipts for August coming in at 401.9 million pounds. The pacing of receipts is 55% above August 2025 due to harvest beginning approximately 2 weeks earlier than prior year. The increase in receipts over last year is not a reflection of projected crop receipts for 2026.
    Nonpareil and Independence varieties are largely harvested with pollinizer varieties following closely behind. In some of the most advanced areas, growers have completed orchard harvest activities and are focusing on post-harvest practices and minimizing water stress to support next season’s crop.

    Current Nonpareil reject levels are the lowest in several years, though ticking up slightly, driven by a third flight of navel orangeworm. Independence rejects are trending higher than last year, mainly due to brown spot from leaf-footed plant bugs.

    Yields are variable in Nonpareil and Independence depending on the region. Speculation on smaller kernel sizes coming into harvest are beginning to be realized. Yields in Nonpareil and Independence receipts are signaling a lower 2026 crop than 2025, as forecasted. There is continued downward pressure on crop potential, which will be informed by pollinizer varieties that hullers are beginning to process. Next month’s report may reflect further shifts to the forecast as pollinizer volume comes in and is accounted for. — Story contributed by Blue Diamond Growers

  • New Investment Aims to Give Growers Another Tool for NOW

    California almond growers know the challenge navel orangeworm brings every season. The pest can reduce crop quality, increase production costs and raise concerns around aflatoxin and marketability. Now, new additional funding is helping continue an industry-backed research effort to advance another tool growers may one day be able to use as part of an integrated pest management program.

    The Foundation for Food & Agriculture Research, the Almond Board of California and Flyttr™ partnered on a nearly $5 million grant to advance development of a biological approach targeting navel orangeworm in almonds and pistachios. ABC is helping fund a portion of the project, reflecting the almond industry’s continued investment in research that supports long-term orchard productivity, crop quality and grower profitability.

    The project centers on Flyttr’s Friendly™ navel orangeworm technology. The concept is simple: release Friendly™ male moths into areas with pest pressure. When those males mate with wild females, no surviving offspring are produced. With continued releases over time, the goal is to reduce the pest population and lower damage pressure in orchards.

    For growers, the significance is not that this replaces today’s best practices. Sanitation, monitoring, mating disruption, timely harvest and well-timed treatments remain important parts of navel orangeworm management. Instead, this research is focused on developing a targeted biological tool that could complement existing programs and help reduce reliance on conventional insecticides over time.

    Navel orangeworm remains one of the costliest pests facing California tree nuts, with industry losses estimated at more than $800 million each year. Damage can affect yield, quality and food safety, which is why the pest continues to be a priority for research, industry collaboration and new technology development.

    Funding from FFAR and industry partners will support the continued work needed to move the technology closer to practical use, including large-scale production systems and field studies. That means the effort is still in development, but it represents an important step toward expanding the number of durable tools available to growers managing navel orangeworm pressure.

    ABC’s role in helping fund this work is part of a broader commitment to support practical, science-based solutions for almond growers. By investing alongside partners, the almond industry is helping advance research that could protect crop value, strengthen pest management options and support the long-term competitiveness of California almonds.

  • Precision Timing Critical for Managing Hull Rot

    With this season’s hull rot treatment window now behind growers, recent research shared by UCCE advisors offers timely guidance for evaluating disease pressure this year and planning more precise management decisions next season. Hull rot remains one of the more frustrating and yield-limiting diseases in California almonds, particularly because its full impact is not always visible in the year it occurs. The research is helping clarify where growers should focus their efforts, especially as the disease complex evolves and growing conditions continue to favor new pathogens.

    Mohammad Yaghmour, orchard systems advisor in Kern County, has been closely tracking changes in the organisms responsible for hull rot. While the disease has long been associated with Rhizopus stolonifer and Monilinia species, the increasing presence of Aspergillus niger is shifting both how the disease develops and how it needs to be managed in the orchard.

    Hull rot follows a classic disease triangle, requiring a susceptible host, a pathogen, and the right environmental conditions. What makes this disease particularly challenging is that all three components are often present at hull split, when almonds are physiologically vulnerable and environmental conditions can favor fungal growth. Infection begins in the hull, but the most damaging effects appear later as the fungus moves into the fruiting wood. Leaves surrounding infected nuts dry rapidly, and the spurs that would produce next year’s crop are killed. In severe cases, entire shoots can be lost.

    This delayed impact is critical. Yield losses are not just tied to visible infection but to the loss of next year’s bearing wood. Research conducted across multiple orchards showed that yield reductions become meaningful once strike levels reach roughly one hundred per tree. At that point, the cumulative loss of spurs begins to reduce the productive capacity of the tree in the following season.

    One of the most important takeaways from this work is that not all hull rot is the same. Each pathogen behaves differently and requires different management timing. Monilinia, which also causes brown rot during bloom, infects earlier and must be managed weeks before hull split. In contrast, both Rhizopus and Aspergillusare primarily driven by inoculum originating in the soil, and infections occur at or shortly after hull split.

    The rise of Aspergillus niger is particularly important for growers in warmer production areas. This pathogen thrives under higher temperatures and has become increasingly common in Kern County before spreading more broadly across the Central Valley. Its symptoms differ subtly from those of Rhizopus. Instead of the gray, fuzzy growth commonly associated with Rhizopus, Aspergillus produces darker, flatter, jet-black spores. It can also lead to internal damage, including black streaking in wood due to toxin production, which contributes to spur and shoot death.

    Understanding when infection occurs has helped refine management recommendations. Research shows that almonds are most susceptible during early hull opening, particularly when the split is still narrow. That window—when the hull has just begun to open—is where infection severity is often highest for Aspergillus. This underscores why spray timing is so critical. Missing that narrow window can significantly reduce the effectiveness of control measures.

    Variety also plays a role. Nonpareil, Butte, and Sonora have shown higher susceptibility, while Monterey and Fritz tend to be less affected under similar conditions. In mixed plantings, this means growers should expect greater risk in Nonpareil blocks and manage accordingly, prioritizing inputs where the return on protection is highest.

    Cultural practices continue to play an essential role in reducing disease pressure. Excess nitrogen has been shown to increase susceptibility, likely by promoting lush growth that favors infection. Careful nitrogen management can reduce that risk. You can learn more about nitrogen management at Almonds.org/NutrientManagement. Similarly, irrigation practices influence disease development. Strategic deficit irrigation has been linked to reduced incidence of Rhizopus, while excessive soil moisture during hull split can increase disease pressure.

    Dust management is another overlooked but important factor. Because Aspergillus and Rhizopus originate in the soil, any activity that creates dust can move spores into the canopy. Equipment traffic during hull split can unintentionally increase inoculum pressure at the exact time tissues are most vulnerable. Reducing dust during this period can help limit infection.

    Fungicides remain a valuable tool, but they are not a standalone solution. Their effectiveness depends heavily on correct timing and proper pathogen identification. Materials in several FRAC groups have shown strong performance when applied at the early stages of hull split. However, applying them too early or too late significantly reduces their value. In most cases, hull split sprays for disease management can be aligned with navel orangeworm treatments, helping to streamline operations.

    For growers, the message is clear: while the opportunity for in-season treatment may have passed, hull rot management is less about any single treatment and more about matching the right tool to the right moment. By using this season’s observations to scout for disease pressure, identify the pathogen involved and plan ahead for precise spray timing, balanced nitrogen, careful irrigation and dust reduction, growers can better protect the fruiting wood that supports next year’s crop and build more resilient orchard systems over time. — Story contributed by the Almond Board of California

  • California Growers Have a New Enemy That’s Spreading Fast

    Golden Mussels have been a silent threat California growers since they arrived in the Delta in 2024. These mollusks reproduce at an alarming rate and don’t require saltwater, meaning they are now clogging up irrigation systems and depriving crops of an already scarce water supply. Jason McKee from Greenleaf Ag spoke with Matthew Malcolm from Malcolm Media Ag Publishing to discuss this latest threat to orchards. Watch this quick video and learn more in Pacific Nut Producer Magazine.

  • Common Tree Disease May Contribute to Reduced Orchard Longevity

    Recent studies conducted by scientists at UCCE and CSU Bakersfield demonstrate that a common disease prevalent in vineyards and orchards may impact long-term orchard longevity of almonds in the southern San Joaquin Valley.  Almond orchards with a high incidence of crown gall, a disease caused by a ubiquitous soilborne pathogen, exhibit high rates of tree failure caused by a newly identified wood rotting disease.

    Crown gall is common in walnut and almond orchards and can be readily identified by the tumors it induces on the roots and crowns of trees. Unless severe, crown gall generally does not cause tree mortality, but may limit tree size, thus affecting overall yield.  Growers with crown gall-affected orchards often replant young trees that exhibit girdling by the tumors but leave mature trees untreated. Within the past decade, however, growers have noticed heightened prevalence of tree mortality due to butt rot in crown gall-affected almond orchards. The butt rot disease is caused by an introduced fungal pathogen, Ganoderma adspersum, that was first reported in California in 2016.

    From 2024 through 2026, UCCE researchers have surveyed over 23,000 almond trees in Kern and Tulare Counties, documenting prevalence of both butt rot and crown gall.  Molecular identification of the butt rot pathogen in each surveyed orchard was conducted by scientists at CSU Bakersfield. The study found that Ganoderma adspersum was the only species of Ganoderma isolated in all surveyed orchards. Additionally, the results indicated that orchards with crown gall were six times more likely to have butt rot disease. Trees with historic or active signs of butt rot also exhibited 1.5 times the mortality rate of healthy trees over a 26-month survey period.

    The results of this work demonstrate that the introduction of the new butt rot pathogen may elevate the importance of crown gall as a predictor of orchard longevity. The implication of this finding is that the planting of crown gall-free rootstocks during orchard establishment may be key to future reduction of risk from G. adspersum. Similarly, Mohammad Yaghmour and Elizabeth Fichtner, Farm Advisors in Kern and Tulare Counties, respectively, found that crown gall was also associated with increased incidence of thousand cankers disease on walnut.  Fichtner has also reported that crown gall is related to heightened root predation by ten-lined June beetle on walnut.

    The current study was conducted with support from the Almond Board of California and as a collaborative effort between UCCE scientists including Elizabeth Fichtner, Santosh Bhandari, Mohammad Yaghmour, and Raymond Mireles, and CSU Bakersfield Professor Isolde Francis and Chance Kophamer, graduate student. — Story by Elizabeth J. Fichtner, UC Ag and Natural Resources

  • Blue Diamond Releases Crop Progress Report

    Blue Diamond Growers release its monthly crop progress report, noting that harvesting conditions began earlier this year due to the impact of the weather.

    Warm summer temperatures dominated the conditions in California’s Central Valley during much of July, with a significant heat wave developing during the final week of the period. Daily maximum temperatures ranged predominately between the mid- and upper 90’s to just over 100 degrees with highest temperatures reported in the southern San Joaquin Valley. Morning lows exhibited greater variability, with readings ranging from the low 50’s to lower 70’s, depending on the degree of cloud cover each morning. Temperatures were amplified by monsoonal moisture traveling northward, bringing occasionally cloudy skies and increased humidity. Increasing daytime temperatures materialized in the final days of the period, marking the start of a significant heat wave. Temperatures were reported to be between 102 to 105 degrees, with higher temperatures forecast for the first week of August.

    The annual return of summertime monsoon flows stirred a bit of apprehension among California’s almond growers, as memories of the challenging 2025 harvest season were rekindled. With that in mind, growers and huller/sheller operators alike worked to complete final pre-harvest tasks during July, focusing on crop maturity that is running well ahead of normal.

    Insect and vegetation management were prime considerations during the period. As noted in our previous report, treatments to protect early harvesting varieties from damage by navel orangeworm were initiated in June, causing the early or advanced crop and pest development. As the crop continues to develop, secondary treatments, intended to catch the insect’s next generation and protect mid and later maturing varieties, were completed in July. As a reflection of the year’s advanced crop development, second treatments have been conducted in roughly the same time frame that initial applications would have been in “normal” years.

    As for other pest issues, observers are reporting increased population of web-spinning mites in the Sacramento and southern San Joaquin Valleys. Control at this stage of crop development presents several challenges and the forecast heat wave promises to expand existing infestations. Treatments targeting almond-damaging ant species have also been performed, including second applications in cases with particularly high populations.

    Observers are reporting widespread instances of red blotch infections in orchards throughout the Central Valley. As may be seen in the photo accompanying this report, if untreated, red blotch can cause severe foliar damage. However, symptoms of this new fungal disease do not appear until 30 to 40 days after infection. Easily spread by airborne spores that are activated by rain events, and potentially by irrigation, this disease spread from a single orchard in Merced County in 2024 to most of the Central Valley by 2025. Orchards that did not receive adequate protection, or any treatments at all are presenting significant symptoms, with the worst infections beginning to defoliate the trees. This is especially problematic in orchards that have been abandoned. Leaf rust, which follows a similar symptomology, has also been observed.

    After delaying or deferring mower passes during the growing season to control costs, vegetation management on the orchard floor became particularly important during the period. Growers must provide for a clean, firm soil surface within the orchard middles (the area between the tree rows), to facilitate an efficient harvest. Where warranted, treatments to control weed regrowth, followed by flail mowers running close to the soil surface, provide the best conditions for a clean harvest.

    Crop maturity also made irrigation management a focal point. Machinery passing through the orchards must be timed between irrigations to prevent rutting of the surface. For those working to employ regulated deficit irrigation (RDI) described in our previous report, the hotter temperatures complicate grower decisions. Under RDI, growers reduce irrigation to one-half of the orchard’s consumptive use for a two-week period at the initiation of hull split. Keeping in mind that water consumption increases as temperatures rise, in extreme cases, normal irrigation scheduling can result in one-half of consumptive use. For those with orchards ready for harvest, water must also be withheld to prevent bark damage during shaking.

    Owing to the advanced crop maturity, harvest operations of the 2026 crop were launched in mid-July. Observers reported the shakers entered the first orchard on July 10 in western Colusa County. Shakers began working in other advanced plantings along the west side of the Sacramento and San Joaquin valleys during the week of July 12 and the first crop to be picked up was delivered to huller/shellers during the week of July 19. For those along the east side and along the Highway 99 corridor, shaking of advanced blocks is expected to begin during the first week of August.

    Growers and observers have noted that hulls have begun splitting in several pollinator varieties, indicating a potentially compressed harvest. However, how the crop will flow though huller/shellers will be determined as more crop arrives in the first weeks of August. Observers have noted thick hulls in many orchards that can potentially reduce flow rates during hulling.

    — Story by Mel Machado, Blue Diamond Growers

  • Leading Entomologist and PCA: How to Control Navel Orangeworm and Aflatoxin

    How can almond, pistachio, and walnut growers control navel orangeworm and reduce aflatoxin risk? UC Cooperative Extension entomologist Houston Wilson joins pistachio and almond grower and pest control adviser (PCA) Joe Coelho and Arielle O’Connor of the Arizona Cotton Research & Protection Council to discuss practical strategies for preventing infestations, limiting crop damage, and reducing the effects of aflatoxin.

    Presented by title sponsor Liphatech and premier sponsor the Arizona Cotton Research & Protection Council.

    Learn more about postharvest fumigation at https://liphatech.com/

  • Honey Bees Can Detect Viruses in Food

    Honey bees encounter viruses in their environments, especially when they forage on flowers and other food sources. Being able to detect viruses is important for reducing infection and the spread of disease. Many insects, including honey bees, can detect viruses indirectly with sick nestmates, but it has been unclear if honey bees can directly detect viruses in food sources.

    To help beekeepers protect their colonies by reducing viral spread, ARS researchers from the Honey Bee Breeding, Genetics, and Physiology Research Unit in Baton Rouge, LA, studied if honey bees could sense viruses such as deformed wing virus, black queen cell virus, and chronic bee paralysis virus in contaminated food sources.

    In an experimental study, the researchers found that when honey bees were presented with the choice between a spiked sugar solution with viruses and a plain sugar solution, the honey bees preferred the virus-spiked solution.

    “These findings demonstrate that honey bees can directly detect the presence of viruses in contaminated food sources, which has important implications for pathogen transmission within pollinator communities and disease management strategies aimed at improving honey bee health,” said Michael Simone-Finstrom, ARS Research Molecular Biologist.

    According to Simone-Finstrom and ARS Research Entomologist Elizabeth Walsh, both co-lead authors of the study, the results highlight the need to control viral infections and spread in bee colonies.

    One major concern is viral spread from Varroa mites, parasitic pests that feed on honey bees. Currently, controlling Varroa mite populations is one of the most effective ways to protect honey bee colonies. Beekeepers can consider changing how they feed honey bees to limit outside insects from getting access to their food, according to Simone-Finstrom and Walsh.

    “Open feeding scenarios where bees from different colonies and other insects, who may carry viruses, get food from the same source may not be in the honey bees’ best interest,” said Walsh. “Beekeepers can consider an alternative like an individual colony feeder where only honey bees from one colony have access to the food.”

    It is unknown what mechanisms cause bees to gravitate towards the contaminated food sources. More research is underway to better understand honey bees’ foraging behaviors and how the viral presence affects their behaviors.

    “The study’s findings will help us with providing data-driven decisions in honey bee management and ecological decisions,” said Walsh. – By Jessica Ryan, ARS Office of Communications

  • Blue Diamond Releases Early June Crop Report

    California’s Central Valley experienced variable weather conditions during May, with wide temperature swings serving as the norm for the period, punctuated by a few days of rain.

    Daily maximum temperatures ranged from the lower 60’s to nearly 100 degrees during the month, while minimum temperatures exhibited more stability, ranging from the lower 40’s on the chilliest mornings to mid-50’s under “balmier” conditions. Brisk winds also blew through the orchards on several days during the month, with sustained speeds at double digit levels and gusts reaching over 20 mph. While skies were clear and dry on the majority of days, late season storms in the opening and closing days of the period brought measurable rain to much of the Central Valley. Rainfall totals were generally limited to a few hundredths of an inch. However, the final storm of the month proved more vigorous. While most areas reported receiving from .25 to .60 inch of rain, a particularly strong cell passing over Yolo County dropped over an inch of rain near the community of Davis.

    May 2026 continued the pattern of late-spring storm systems that began in April. Grower activities were largely focused on vegetation management, fertilization, and irrigation, which was offset by adequate rainfall in some cases. While the wet conditions have increased concerns for fungal infections on the foliage and developing nuts, most growers feel that they have adequate protection provided by previous treatments. The rain events have limited the expansion of web-spinning mites and observers are reporting that the orchards are in generally good condition in all areas of the valley. Areas with the strongest winds experienced some blown-over trees, broken branches, and nut loss. However, losses have been minimal.

    Kernels in all varieties became fully solidified during the month, providing the first confirmation of the crop maturity since the completion of the bloom. There is now strong solidarity that the crop is running approximately 10 days ahead of “normal” in all areas. While June temperatures can influence exact timing, many believe the hull split will follow the current advanced timing, with the split in advanced examples of early maturing varieties expected during the week of June 21.

    As May concludes, many growers were winding down applications of fertilizer materials, and mowing vegetation in the orchard middles to manage the orchard floor in advance of the upcoming harvest. Growers whose orchards have high populations of almond feeding ants have begun the earliest treatments using bait formulations to target them. Some of these materials require several weeks to effectively reduce the ant populations and need to be applied as much as eight weeks prior to harvest.

    Growers and their pest control advisers, (PCAs), have been monitoring orchards for signs of leaffooted plant bugs and stink bugs. Brown spot, the damage resulting from the feeding of these insects on the developing nuts has been increasing for several years. Pheromones have been developed and are being tested in orchards to combat leaffooted plant bugs as PCAs work with university researchers to develop protocols for implementation. Growers have treated increasing populations of these insects where warranted.

    Growers have also begun preparations for hull split treatments to control navel orangeworm (NOW). In anticipation of the advanced timing this year, growers are shifting their attention to spotting the discoloration and splitting of blank nuts at the top of the orchard canopy and along the tree rows at the edge of the orchards. These blanks (nuts that formed a hull and shell but were not fertilized during the bloom and have no kernel) split approximately ten days ahead of the sound nuts that contain almond kernels. These serve as a signal of the approaching hull split. By monitoring the split of blank nuts, growers and their pest control advisers can fine tune treatment timing during the split to optimize control.

    Low and minimal care orchards, as well as abandoned plantings, are present in all areas. Pest management programs have grown complicated for many growers managing plantings near abandoned/low care orchards due to adult NOW moths moving into their orchards to lay eggs on the splitting hulls. Orchard sanitation (the reduction of NOW residing within the orchards) is the foundation of NOW management. NOW adults migrating from nearby sources have created significant financial hardship and mounting frustration for growers in recent years. — Story contributed by Blue Diamond Growers

  • Annihilating Nematodes in the Tree Nut Orchard

    Farmer John Chandler lamented the loss of methyl bromide for replanting an orchard or vineyard. Photo credit: Diana Gutierrez

    Andreas Westphal, scientist at Kearney Agricultural Research and Extension Center in the San Joaquin Valley, organized a soil plant pathology conference that was held on March 24-26, 2026. Participants from as far away as Virginia came to learn about the latest research findings.

    Chandler Farms

    The first day of the conference was a field tour to three sites and then Kearney itself. After meeting at Kearney, the participants rode on a tour bus to Chandler Farms in Selma. John Chandler, his brother Tom and their father, Bill operate a diversified farm that includes almonds, grapes and citrus.

    Soil Fumigants

    The Chandlers typically change out one field per year. John lamented the loss of methyl bromide for replanting an orchard. He now uses Telone, which he finds “has less effect but still works.” 

    He always contracts out his Telone application because it requires special training. He has the contractor put tarps over it, beyond the usual seal, to prevent off-gassing, but he says, “It’s not worth it to get acres of plastic.” The tarps add about $1000/acre to the cost.

    Westphal explained, though, that Telone is becoming more difficult to use because of a new restriction in the amount of Telone allowed plus a requirement that the fumigant be applied with lots of water.  The new regulations say that the soil has to be wet to two feet depth. If the soil is bone dry, three inches of water must be added within 72 hours before applying the fumigant.

    However, the excess water makes it hard to get a tractor through the field. Also, the fumigant does not move well through water, as it is made to move through air. Lastly, the Telone stays in wet soil longer before vaporizing off, which may make it toxic to plants.

    Nematodes     

    Chandler said that his farm has nematodes —the microscopic roundworms that feed on plant roots. His soil has root-knot, lesion, ring and citrus types of nematodes.

    When he can afford it, he fallows the land for a year or two instead of fumigating, but he says that fumigation gives the plants the best chance to get started. Once the crop is established, he notes, there are few tools for nematode adjustment.

    Burchell Nursery

    The second stop was Burchell Nursery in Fowler, where Mauricio De Almeida led the group around the almond, stone fruit, citrus, pomegranate, and retail table grape plants.

    Mauricio de Almeida led the tour group around the almond, stone fruit, citrus, pomegranate, and retail table grape plants at the Nursery. Photo credit: Diana Gutierrez

    What is gnawing the plant roots?

    Almeida said that, as in all greenhouses, the water, heat and humidity may induce root rot and fungus gnats. The fungus gnat larvae eat the soft tissue of plant roots. The adults do not feed on plants.

    Another larva that Burchell manages is that of the European pepper moth. The caterpillars girdle the plant stem below the soil line.

    The root rot and insect pests occur even though the potting media — made of peat, bark, wood fiber and sometimes Perlite — comes pasteurized. The nursery uses Nemasys® beneficial nematodes to manage the larval insect pests.

    Almonds

    In almonds, Bright’s Hybrid 5, Hansen and Viking rootstocks and Shasta scions resist root-knot nematode. Viking and Shasta also tolerate ring nematodes. Bright’s Hybrid also has low susceptibility to root lesion nematodes. In susceptible varieties, root-lesion nematodes create lesions that can lead to secondary infections like bacterial canker.

    The visitors got to see the Cornerstone cultivar of Prunus rootstock, developed by Burchell Nursery to resist the root knot nematodes Meloidogyne javanica and M. incognita. Used as rootstock for almond and stone fruits, Cornerstone is also less sensitive to crown gall, caused by Agrobacterium tumefaciens.

    Unfortunately, in both Kern and Merced counties (but not Fresno County where the tour took place), in 2018 a root-knot nematode from Florida, Meloidogyne floridensis, was found in almond trees on Hansen 536 and Bright’s Hybrid 5 rootstocks, where they caused growth decline of the trees. Now considered an A-rated (“highest concern”), quarantined pest in California, it has since been found in South Carolina and Georgia, after being considered endemic to Florida before 2018.

    After a visit to the Cobblestone citrus packing plant, the tour group boarded the bus a final time to return to the Kearney Agricultural Research Center and ate sandwiches for lunch.  They then rode on a tram to visit different field research plots at the Center.

    Levels of Plant Response to Pathogens

    Plants can be divided into three groups of responses to nematodes and other pathogens: sensitive, tolerant and resistant. Tolerance allows for high nematode populations, which gives the nematodes more opportunity to have genetic mutations that enable them to overcome the plants’ resistance. Therefore, nematicides should be used in tolerant cultivars to limit the pest population.

    Walnuts and Almonds

    Walnuts are sensitive to some nematodes and resistant to others, but “every plant has its limits,” Westphal said. Walnut soil is treated pre-plant and at-plant at the planting site.  Tank water is used to settle the tree in. Salibro is added to the tank water to form a concentration that kills the nematodes but not the trees. Westphal cautioned growers to not overwater walnuts.

    Among other things, Westphal is testing juice from walnut hulls to see if they inhibit nematodes.  He noted that ASD (anaerobic soil disinfestation), created by applying nine tons of rice bran per acre, inhibited nematodes somewhat. However, it would not be worth the $6,000/acre price tag for growers.

    Westphal is testing whether juice from walnut hulls can inhibit nematodes in almond orchards.

    Highly resistant rootstocks can grow without fumigation, with less toxic, affordable nematicides applied.  As with citrus, nursery trees must be grown in nematode-free soil, or the trees must be certified before leaving the premises.

    Westphal showed the tour participants an almond rootstock test orchard, in which nematode resistance is compared among various commercial and experimental rootstocks.  Only the most successful experimental rootstocks make it to the next round of trials, along with the commercial ones for comparison.

    Westphal then concluded the field tour.  The conference continued indoors on the following two days.  — by Nancy Power, Assistant Editor