Pacific Nut Producer Magazine

Tag: University of California

  • Almond Orchards Prevail in Battle with Phytophthora

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    Losing crops is a reality of farming, especially when you’re battling weather, new pests and emerging diseases. Seeing a few acres of your life’s work perish is tough, but the threat of losing your entire operation is a different type of sting. One California almond grower shares how soil health improvements made his orchards vulnerable to disease and how he was able to bring them back from the brink of total devastation.

    Trees Lost to Unusually Wet Weather Worsened by Soil Prep

    Whole orchard recycling is a process to reincorporate an outgoing orchard in preparation for planting a new one. Mature trees are felled and ground into woodchips, which are then spread and incorporated into the soil. The University of California found that this process can help improve water retention. The issue for John Fassler, a California pest advisor who went through whole orchard recycling, was that the moist soil and greater-than-normal rainfall turned his orchards into the perfect breeding ground for oomycete pathogens like Phytophthora.

    Fassler has consulted at Braden Farms where they used whole orchard recycling as a way to prepare for planting a new orchard. “This is a fairly new process, which means we’re learning as we go,” he says. “Some issues we’ve seen have been a rise in fungal diseases, such as Phytophthora and other replant diseases.”

    Mother Nature hasn’t helped the fungal disease risk, especially at the beginning of the 2023 growing season. California experienced greater than average annual precipitation in 2023, breaking numerous records and ending three years of persistent drought, according to the California Nevada River Forecast Center.

    “We’ve had significant rainfall in California the last two years, so this has really intensified the battle with Phytophthora in some spots,” says Ashley Bandoni, Syngenta sales representative and California almond grower.

    Fassler experienced devastation due to those heavy rains. One of his orchards was completely submerged, worsening the orchard’s Phytophthora issues.

    “We lost about 500 trees on this block due to Phytophthora and replant disease,” says Fassler. “Phytophthora is becoming more and more of an issue in these wetter years.”

    Watch Video

    Phytophthora Overtakes Young Almond Trees

    Many California growers and crop consultants have been battling fungal disease challenges.

    Ethan Nicol, an independent pest control advisor and crop consultant for Balanced Agronomics, helped one of his customers manage extreme Phytophthora in a young almond orchard.

    Planted in the fall of 2021, Nicol began seeing early symptoms of Phytophthora infections the following spring. Young trees like the ones in the orchard Nicol manages tend to be more susceptible to disease because their root systems and crown areas are smaller compared to those of mature trees, according to the University of California Department of Agriculture.

    “In that first 2022 season, we observed maybe 30 percent of the orchard was infected,” says Nicol. “By mid-August, we had really grown to realize the significance of the issue.”

    Watch Video

    Coming Back from Orchard Devastation

    For both Nicol and Fassler, almond yield potential was on the line and devastation was just over the horizon. They both had a tough decision to make.

    “As far as doing our research going into it, usually we have the Syngenta reps come in to help us decide if the product will be a good fit for us,” says Fassler. “We also ask about how the product differentiates itself from what we’ve already been doing.”

    After discussions with their local Syngenta experts, Fassler and Nicol decided to apply Orondis® fungicide to help save their orchards. Fassler says his flooded orchard plot turned around.

    “My experience with Orondis changed up our program,” says Fassler. “We’ve been able to work it into our program really well and we didn’t lose one tree this year.”

    Nicol’s experience with Orondis was also nothing short of extraordinary. Before application, Nicol was working with the grower to continuously remove and replant dead trees. They lost roughly 600 almond trees — six ranches — to Phytophthora. Once Orondis was applied in 2023, Nicol observed a noticeable decline in newly infected trees.

    “We were confident in the success that we were seeing by the replants taking and growing strongly, and the existing trees continuing to grow and not develop signs of Phytophthora,” says Nicol. “Going into 2024, just as a precaution and to help protect this investment, we made an additional Orondis application. There’s been almost no sign of infected trees this season.”

    Growers Also Need Care

    If Fassler and Nicol didn’t have the guidance and support of their Syngenta representatives, their almond orchards might have been lost.

    “I’ve worked with Syngenta for probably about the last 20 years, and through the years we’ve had many different experiences,” says Fassler. “Syngenta has always been there to help us through and guide us through what needed to be done.”

    Learn more HERE.

  • Bacterial blast/canker: What do we know?

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

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

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

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

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

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

  • Using the Sun & Agricultural Waste to Control Pests

    Biosolarization Shows Promise for Conventional & Organic Farmers

    By Diane Nelson

    Farmers spend a lot of time and money controlling weeds and other pests, and often have to turn to chemical fumigants to keep the most destructive pests at bay. Farmers also wrestle with what to do with low-value byproducts of crop production, such as skin, seeds and hulls from fruit, vegetable and nut processing.

    What if those agricultural waste streams could generate alternatives to chemical fumigants and make farming more productive, profitable and environmentally friendly?

    Maybe they can. Researchers at the University of California, Davis, are encouraged by early results from collaborative experiments with “biosolarization,” a process that combines the sun’s heat with soil amendments to manage weeds and other soil-borne pests.

    “It looks promising,” said food science and technology professor Christopher Simmons, who is testing biosolarization with various crops and working with farmers throughout the state. “We still have a lot of work to do, but biosolarization is showing real potential as a safe, sustainable way to control pests while improving crop quality and yield.”

    Strengthening solar power   

    Many backyard gardeners know the power of solarization. When you lay a clear plastic tarp over moist soil, you can trap solar radiation and heat the soil enough to kill weeds and other soil-borne pests. It’s effective, but can take four to six weeks, which is often too long for commercial fields to lay fallow.

    Biosolarization can accelerate and improve the process. Simmons and his team are adding organic amendments such as grape and tomato skins or ground nut hulls to the soil before they tarp it, which promotes growth of beneficial bacteria. The helpful microorganisms compete with pests and temporarily make the soil more acidic and therefore less hospitable to weeds and other pests.

    Together, the soil-heating and microbial activity can reduce the treatment time to days, not weeks.

    “And by activating beneficial microbes in the soil, biosolarization has the potential to improve soil health over the long term,” Simmons explained.

    Testing under commercial conditions

    Chemical fumigants are expensive, and many have been identified as carcinogenic by state and federal regulatory agencies. But when it comes to killing soil-borne pests, they are very effective.

    “Fumigants are broadly biocidal, meaning they affect beneficial microorganisms along with the pests,” Simmons said. “Biosolarization allows more innocuous and beneficial microorganisms to persist in the soil.”

    But for farmers to adopt biosolarization as an alternative to chemical fumigants, the treatment must be effective, predictable and economical. So the team is testing biosolarization with a wide variety of crops, amendments and soils against different pests in various locations at commercial scale throughout the state.

    “We have field trials underway with lettuce, tomatoes, melons and various cover crops,” Simmons said. “And we have a long-term, 10-acre trial with almonds at a conventional orchard in Chico.”

    In Chico, Simmons and his team are collaborating with almond grower Rory Crowley at Nicolaus Nut Company with funding support from the Almond Board of California and the Western Center for Agricultural Health and Safety. They are one year into a 25-year experiment to see if almond-processing residues and the sun can boost soil health and reduce weeds and other soil-borne pests. So far, Crowley is impressed.

    “It’s been great for the soil,” Crowley said. “Using biosolarization and a mustard cover crop, we’ve increased organic matter by 1.25 to 1.75 percent, which is a huge jump. That’s good for carbon sequestration and the overall health of the soil.”

    It’s too soon to tell if the soil improvements will translate to greater crop yield, but Crowley thinks biosolarization could become a good pest-management tool and a valuable use for what would otherwise be agricultural waste.

    “We need to find a home for the co-products of almond processing, so why not see if we can use them to improve soil health while controlling pests?” Crowley asks.

    Field tests continue

    Simmons and his team are testing biosolarization on several annual and cover crops in plots on the UC Davis campus using agricultural waste streams from tomato and wine processing. Soon they will begin tests with strawberries, which are commonly treated with fumigants each season as farmers plant berries anew.

    Simmons’ hope is to demonstrate to farmers that biosolarization can be effective and economical under a wide range of conditions against a broad number of pests.

    “We’re making significant ground,” he said. “We’re hopeful biosolarization can help farmers return food and agricultural waste back into the system to control pests and improve crop production.”