Pacific Nut Producer Magazine

Category: Irrigation

  • Phytophthora Sampling in the Stockton East Water District

    This work was partially funded by the Stockton East Water District — Crown rot and root rot caused by Phytophthora species are diseases of great concern for almond growers. Many people believe that irrigating with surface water puts your trees at risk of Phytophthora, and that irrigating with groundwater is the best way to prevent these diseases. However, a recent study of Phytophthora in irrigation water and orchard soils tells a different story.

    The Bottom Line:

    Irrigation management is Phytophthora management. This study showed that Phytophthora is common in orchard soils. Regardless of whether they are irrigated with surface water or groundwater, over 30% of tested orchard soils were positive for Phytophthora. Since water (either standing water or saturated soil) allows Phytophthora to cause disease, good irrigation management is crucial to prevention, no matter what your water source.

    — Reduce ponding: irrigation application rate should not exceed soil infiltration rate.

    —Reduce length of soil saturation: run shorter sets (24 hrs max) more frequently.

    — Avoid water on the trunk of the tree and avoid soil saturation at the trunk: plant on berms, use stream splitters, choose microsprinkler wetting patterns that avoid the trunk, move drip emitters away from the trunk.

    Using a resistant rootstock is an excellent tool to help limit Phytophthora disease if you are planting a new orchard (see this chart for rootstock info) or putting in replants. Even with a resistant rootstock, good irrigation management is crucial because no rootstock is immune.

    The Details:

    Phytophthora is a genus of fungus-like organisms which contains over 200 different species. Many of these species are important pathogens of orchards, causing root rot or crown rot (for example Phytophthora cinnamomi, Phytophthora cactorum, and Phytophthora mediterranea) or pruning wound cankers (mainly Phytophthora syringae). Many previous studies have shown that Phytophthora species are common in surface sources of irrigation water, such as rivers, canals, and sloughs. Phytophthorahas not been found in groundwater from wells, unless that well has been contaminated with surface water. From this, people have assumed that irrigating with surface water puts an orchard at risk of Phytophthora root or crown rot, and that irrigating with groundwater is ”safe.” However, biology is rarely that simple: in my experience, orchards irrigated with groundwater can struggle with Phytophthora, and many orchards irrigated with surface water do not show symptoms of Phytophthora disease.

    In 2021 and 2022, collaborators and I conducted a study to look at the effects of Phytophthora in irrigation water from a broader perspective. This study took place in the Stockton East Water District (SEWD), a local water agency that manages both groundwater and surface water use by agricultural producers east of Stockton, CA. The study had three objectives:

    — Test SEWD surface water for Phytophthora during the irrigation season.

    — Test for live Phytophthora coming through irrigation emitters.

    — Test orchard soils for Phytophthora, comparing orchards irrigated with surface water vs groundwater.

    Objective 1. Test SEWD surface water for Phytophthora during the irrigation season

    During the 2021 irrigation season, we sampled water from surface water irrigation sources throughout the SEWD. Some locations (core sites) were sampled monthly from June through October, and some locations (additional sites) were sampled twice during the season, in July and October. Samples were taken back to the lab and tested for Phytophthora using DNA sequencing.

    Overview of the Stockton East Water District (SEWD) with water sampling sites marked.

    We found that Phytophthora species were common in SEWD waterways. Over the course of sampling, we found 39 Phytophthora species, 10 of which are known pathogens of orchards crops grown in the SEWD. Many of these species were found throughout the irrigation season. We did find that different waterways had different Phytophthora species, and some waterways had more orchard pathogens than others. However, every waterway, and nearly every site, had at least one Phytophthora species of concern to orchards. These results are consistent with many previous studies, which have determined that Phytophthora species are common in surface sources of irrigation water.

    Phytophthora species detected in Stockton East Water District waterways throughout the irrigation season.

    The Phytophthora species listed in this table are reported to cause disease on walnut (W), cherry (C), almond (A), or pistachio (P). If the crop is bold, the Phytophthora species is particularly aggressive on that crop. A plus (+) indicates that the Phytophthora species was detected at least once in that waterway. A period (.) indicates that the species was not detected in that waterway. Nineteen other Phytophthora species (not listed) were detected, but these are not known to cause disease on orchard crops.

    Objective 2. Test for live Phytophthora coming through irrigation emitters

    In objective 1 we determined that Phytophthora is common in the SEWD waterways. However, very few studies have looked at whether Phytophthora in a waterway can get into an orchard through the irrigation system. This is especially true of drip irrigation systems, which require substantial filtration of surface water to keep emitters from plugging.

    During the 2021 and 2022 irrigation seasons, we collected water directly from irrigation emitters during a normal irrigation and tested this water for the presence of live Phytophthora. This was done in three surface-water-irrigated orchards, two with drip emitters and one with sprinklers, as well as two groundwater-irrigated orchards, one with drip emitters and one with sprinklers.

    Orchard sampling stations used to detect live Phytophthora in water from A, sprinklers and B,

    drip emitters.

    We found that Phytophthora commonly survives the journey from surface water sources into the orchard, and that the irrigation system type did not seem to matter. Also, the presence of a sand media filter did not seem to affect how regularly we detected live Phytophthora coming through irrigation emitters.

    Summary of Phytophthora detections in water collected from irrigation emitters

    Objective 3. Test orchard soils for Phytophthora, compare orchards irrigated with surface water vs groundwater

    In objectives 1 and 2 we determined that Phytophthora is common in SEWD waterways and that it can survive the trip through an irrigation system and into the orchard. However, in most cases Phytophthora must survive in the soil to infect the orchard when conditions are right. Even though we knew that irrigation with surface water is bringing Phytophthora into orchards, we didn’t know if this affects the incidence of Phytophthora in orchard soils.

    In 2021, we collected soil from 20 SEWD orchards exclusively irrigated with groundwater for at least 60 years and from 20 SEWD orchards mainly or exclusively irrigated with surface water over the same timeframe. This soil was tested for the presence of Phytophthora species using both the DNA sequencing from objective 1 and the live detection methods from objective 2.

    We found that Phytophthora is common in orchard soils, with 32.5% of sampled orchards (13 out of 40) testing positive. We also found that the source of irrigation water did not affect the chances of finding Phytophthora in the soil: groundwater irrigated orchards were as likely to have Phytophthora as orchards irrigated with surface water. This indicates that irrigation with surface water was not the main factor determining whether Phytophthora was present in orchard soils and that irrigation with surface water may not increase risk of Phytophthora disease in orchards.

    Hytophthora species in bold are particularly aggressive on orchard crops

    The results from this study confirm that Phytophthora is common in surface water but show that irrigating with surface water was not the main factor determining whether Phytophthora was present in an orchard. Where is the Phytophthora coming from? It is hard to know, but historical flooding may play a role. We also know that Phytophthora can be moved into an orchard on planting material and in soil on equipment. Where does this leave us in terms of management? This study shows that Phytophthora is very common in orchard soils, regardless of the source of irrigation water. Since over 30% of tested orchards were positive for Phytophthora, it would be prudent to assume you have Phytophthora in your orchard. Saturated soil allows Phytophthora to infect and cause disease, so good irrigation management is crucial to prevention. By “good irrigation management”, I mean that you want to reduce the length of time that orchard soils are fully saturated and avoid having standing water. This can be done by using irrigation emitters with output volumes suited for your soil infiltration rate and by irrigating more frequently for a shorter duration (24 hrs maximum). In addition, you want to apply irrigation water in the root zone but away from the trunk to reduce the opportunity for infection of the trunk or major roots. This can be done using stream splitters with sprinklers to protect the trunk, choosing a microsprinker wetting pattern that avoids the tree trunk, or moving drip emitters away from the trunk of the tree. At planting, consider using a resistant rootstock, and plant on berms. Note that even if you are using a resistant rootstock, good irrigation management is crucial because no rootstock is immune.

    I want to leave you with this thought: irrigating well is much more important for preventing Phytophthora than the source of your irrigation water. I have been to many surface-water-irrigated orchards with no symptoms of Phytophthora. Some of the worst orchards I have seen, in terms of Phytophthora disease, were irrigated with groundwater with the driplines right against the trunk on 3rdleaf trees. Irrigation management is Phytophthora management.

    Thank you to my collaborators on this project, Greg Browne (USDA-ARS) and Mohamed Nouri (UCCE San Joaquin County). Special thanks to Justin Hopkins with the SEWD for his help planning and executing this project. Thank you also to the SEWD growers who welcomed me into their orchards for sampling. This work was partially funded by the Stockton East Water District. — By Jaime Ott, UC Extension Tehama, Shasta, Glenn, and Butte Counties

  • Five Ways to Avoid Expensive Irrigation Repairs & DU Losses

    Irrigation systems today are amazing at getting just the right amount of water where it needs to be to meet a crop’s needs; however, if these systems are not well-maintained, things can go south pretty fast, resulting in distribution uniformity-related losses and expensive repairs. During his presentation at Malcolm Media’s recent Tree & Vine Expo, UC Cooperative Extension Irrigation & Soils Advisor Moneim Mohamed noted that regular and proper irrigation system maintenance can prevent expensive repairs.  Watch his video interview with Matthew Malcolm on California Ag Network for five key tasks for preventative maintenance.

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

  • Walnuts Deemed “Healthy” By the U.S. Food & Drug Administration

    Walnuts meet the updated definition for a “healthy” food based on the important role they play in recommended dietary patterns, according to the much-anticipated announcement from the U.S. Food and Drug Administration (FDA) detailing a new definition for foods that can be identified or labeled as “healthy.”1

    This announcement, originally previewed in 2022 on the heels of the historic White House Conference on Hunger, Nutrition and Health, is a significant step toward ensuring food labeling is consistent with the most up-to-date nutrition scientific evidence and Dietary Guidelines for Americans (DGA) recommendations to support individuals and families in building healthy eating patterns.

    “The inclusion of walnuts in the new “healthy” definition affirms consumers’ belief that walnuts are a healthy food.* It also aligns with decades of nutrition research reinforcing the important contributions walnuts can make in a healthy lifestyle,” shared Robert Verloop, chief executive officer for the California Walnut Commission.

    “It’s simple. Just adding walnuts to Americans’ daily diet can potentially have wide-ranging positive impacts.”

    The 2020-2025 DGA encourage consumers to choose foods that are nutrient-dense, such as nuts, including walnuts. However, close to two-thirds of Americans do not meet the recommended intake for nuts and seeds.2,3

    Encouraging walnuts as a substitution for food choices higher in saturated fat can help support recommendations to replace intake of saturated with unsaturated fats, as strongly advised by the recently-released 2025 Dietary Guidelines Advisory Committee Scientific Report.4 The total fat in walnuts (18g) is mostly comprised of polyunsaturated fats (13g/oz), including omega-3 ALA (2.5g/oz), an essential fatty acid with potential to support heart health and cognition.5-7 Walnuts are the only tree nut to provide an excellent source of omega-3 ALA.8 

    “In my 20 plus years of practicing nutrition at a major medical institution, I have seen trends go in and out for what the public considers healthy. But what has always been foundational is the role plant-based foods like walnuts play in supporting health. Walnuts are one nut I find consistently meets the variable needs of patients in my practice,” states Kristin Kirkpatrick, MS, RDN and author. “In practice, I focus on evidence-based approaches to reducing chronic disease risk, weight management, and improvements in metabolic health.”

    Walnuts qualifying as a “healthy” food is just one major milestone in a series of similar recognitions. A recent ruling, earlier in 2024, by the USDA’s Food and Nutrition Service (FNS), ‘Child Nutrition Programs: Meal Patterns Consistent With the 2020-2025 Dietary Guidelines for Americans,’ will make it easier for schools to serve plant-protein rich meals and snacks that include walnuts. Using ingredients like walnuts can help reformulate meal favorites to be healthier, while also supporting vegetarian diets and other food preferences.  Additionally, for the first time, states are now allowed to include walnut butter as part of the latest WIC program (Special Supplemental Nutrition Program for Women, Infants, and Children)package updates. 

    These new inclusions and acknowledgements of the role of walnuts in healthy dietary patterns are due, in part, to the more than 30 years of evidence-based global health and nutrition research funded by the California Walnut Commission. This growing body of research has uncovered many potential benefits of consuming walnuts within healthy dietary patterns across various ages and life stages to maximize health and well-being, including promising research into heart health, cognition, cancer, gut health, body weight, and reproductive health.

    Walnuts are extremely versatile and convenient, adding nutrition to dishes at every meal, as well as simple snacks. For more information about the nutritional benefits of California walnuts, along with delicious recipe inspiration, please visit walnuts.org.

    About the California Walnut Commission 

    The California Walnut Commission (CWC) represents more than 4,600 California walnut growers and approximately 70 handlers, grown in multi-generational farmers’ family orchards. California walnuts, known for their excellent nutritional value and quality, are shipped around the world all year long, with more than 99% of the walnuts grown in the United States being from California. The CWC, established in 1987, promotes usage of walnuts through domestic and export market development activities as well as supports health research with consuming walnuts.

    To explore recipes and learn more about California walnut growers, industry information and health research, visitwalnuts.org.

    * California Walnut Board 2021 Consumer A&U

    References

    1. Public Inspection: Food Labeling: Nutrient Content Claims; Definition of Term ‘Healthy.’” Federal Register, 2024, www.federalregister.gov/public-inspection/2024-29957/food-labeling-nutrient-content-claims-definition-of-term-healthy. Accessed 20 Dec. 2024.
    2. U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. Available at DietaryGuidelines.gov.
    3. Analysis of What We Eat in America, NHANES 2013-2016, ages 1 and older, 2 days dietary intake data, weighted. Recommended Intake Ranges: Healthy U.S.-Style Dietary Patterns.
    4. 2025 Dietary Guidelines Advisory Committee. 2024. Scientific Report of the 2025 Dietary Guidelines Advisory Committee: Advisory Report to the Secretary of Health and Human Services and Secretary of Agriculture. U.S. Department of Health and Human Services.
    5. Sala-Vila A, Fleming J, Kris-Etherton P, Ros E. Impact of alpha-linolenic acid, the vegetable omega-3 fatty acid, on cardiovascular disease and cognition [published ahead of print February 16, 2022]. Advances in Nutrition. doi.org/10.1093/advances/nmac016.
    6. Naghshi S, Aune D, Beyene J, et al. Dietary intake and biomarkers of alpha linolenic acid and risk of all cause, cardiovascular, and cancer mortality: Systematic review and dose-response meta-analysis of cohort studies. BMJ. 2021;375:n2213. doi:10.1136/bmj.n2213.
    7. Barceló-Coblijn G, Murphy EJ. Alpha-linolenic acid and its conversion to longer chain n3 fatty acids: Benefits for human health and a role in maintaining tissue n-3 fatty acid levels. Prog Lipid Res. 2009;48(6):355-74. Doi.org/10.1016/j.plipres.2009.07.002.
    8. U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, 2019. Fdc.nal.usda.gov.

  • Postharvest State of the California Walnut Industry Highlights Improving Market

    Did you miss the State of the Walnut Industry address at Malcolm Media’s recent Grape, Nut & Tree Fruit Expo in Fresno or the Tree & Vine Expo in Turlock?  Following his presentation, Robert Verloop, CEO of the California Walnut Board & Commission met with Matthew Malcolm on California Ag Network to share highlights from this year’s walnut harvest and improving global market conditions. Watch this brief interview, and read the full State of the Industry report in the coming issue of Pacific Nut Producer Magazine.

  • California Farmland to Serve State in Recharging Groundwater Supply

    The Governor of California recently issued an Executive Order allowing local water districts to utilize floodwater for groundwater recharge purposes, a record amount of which will take place on California farmland.  This is desperately needed and welcomed by farmers and other water users all over the state that have suffered decades of drought conditions.  Watch this brief interview with Adam Borchard from the California Fresh Fruit Association for more insight on what the announcement entails.

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

  • Pacific Nut Producer October Issue

    PNP1022
    Pacific Nut Producer October Issue

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    Contents of the October Issue:

    Mark Hutson Farms a Canvas of Possibilities
    Takes Water Future into his Own Hands with On-Farm Recharge
    The Irrigation Corner
    Salt Removal from Drip/Micro Irrigated Orchard Soils
    A New Era of UCCE Farm Advisors
    UC Ramping Up California Tree Nut Extension Efforts
    October Orchard Tasks
    Almonds, Hazelnuts, Pecans, Pistachios, Walnuts

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  • Pacific Nut Producer September Issue

    PNP922
    Pacific Nut Producer September Issue

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    Contents of the September Issue:

    Pistachio Luncheon Offers Great Insights
    APG Plans & Markets Ahead of Increasing Pistachio Production
    The Irrigation Corner
    Understanding Soil Salinity Accumulation in the Orchard
    The Curious Case of Macadamia Quick Decline
    Uncovering the Culprit Decimating Hawaii’s Nut Trees
    September Orchard Tasks
    Almonds, Hazelnuts, Pecans, Pistachios, Walnuts

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  • A Proactive Approach to Orchard Planting

    – SPONSORED CONTENT –

    California’s orchards are a vital part of the local economy, providing over half of the fruits and nuts we consume daily. The caretakers of these orchards work tirelessly to provide us with healthy, nutritious foods. Tree nut growers play a dual role in the health and safety of the communities in which they live, work and play – providing food and promoting safety.

    By planting new orchard trees that are compatible with power lines, growers can ensure safe and reliable power for the 16 million Northern and Central California residents who depend on it.

    Planting a new orchard is an important investment – one that growers consider carefully, after thorough thought and planning. Sometimes, planning new plantings around power lines is a missed step in the orchard planning process.

    Pacific Gas & Electric (PG&E) works with growers to plan before they plant, identifying power line-friendly planting locations early in the orchard planning process to help growers maximize their investment. Together, tree nut growers and PG&E can reach safe solutions that help meet growers’ needs while protecting electric system reliability and making sure California communities remain safe.

    In addition to keeping communities safe, taking a proactive approach to orchard planning helps growers avoid spending needlessly on land in incompatible areas; installing irrigation systems in right of way areas and planting trees that will ultimately require removal.

    Plan Before You Plant resources are available for growers to learn more about the importance of maintaining safe distances from transmission lines. Reach out early in your orchard planning process to schedule a visit to your orchard to have an expert identify power line friendly planting locations near transmission lines.

    For more information, visit www.pge.com/planbeforeplanting or call 1-800-743-5000.