California Ag Network

Tag: Walnut Orchards

  • 2025 Results of Pre-Emergent Herbicide Demonstration Trial for Walnut

    The 2025 UCCE walnut pre-emergent herbicide demonstration trial is completed, and the results show strengths and weaknesses of 19 different herbicide treatments, applied either in February or March.

    Takeaways:

    1. All treatments were applied with a strong post-emergent mix, but hairy fleabane and white clover were not adequately controlled with post-emergent treatments alone. Control was dependent on the addition of an ALS inhibitor herbicide (products like Craze, Matrix, or Mission).

    2. Summer annual weeds were best controlled by products with long residuals (products like Alion, Chateau, Brake On! (not registered in CA), and Prowl.

    3. Yellow nutsedge was controlled by treatments with Zeus or Craze.

    4. Conclusion: Pre-emergent treatments in late winter must account for winter annual weeds that have already emerged and perennial weeds while also maintaining good residual control further into the summer.

    Introduction

    Winter pre-emergent herbicide applications are critical to get right if yearly weed management operations are going to be successful in walnut orchards. Poor selection of herbicides or missed timing could make the difference between good control and battling an overwhelming infestation of weeds. In walnut orchards I have regularly heard two comments concerning pre-emergent herbicide applications in walnut orchards:

    1. Those who apply pre-emergent herbicides in the fall, just after harvest, tend to have the cleanest orchards.

    2. February or March are the most common times to apply pre-emergent herbicides in walnut orchards.

    Maybe my perception is incorrect, but these weed control strategies seem to be at odds. When it comes to winter annual weeds, it is likely safest to apply pre-emergent herbicides before germination due to several common weed species with herbicide resistance issues (hairy fleabane, Italian ryegrass, annual bluegrass). Applications later in the winter will have to deal with emerged weeds, potentially resulting in more escapes and misses.

    However, herbicide treatments in February or March are common, and many growers have been successful with these treatments. Why is this, and what is the key to achieving good control later in the winter? Success at later timings depends on how much post-emergent activity you are getting out of your tank mix. Some pre-emergent herbicides can contribute to your post-emergent activity. Common pre-emergent herbicides like Goal, Chateau, Matrix, Pindar, and others add some extra post-emergent activity to tank mixes when used in winter months. Dr. Brad Hanson (UCCE Weed Specialist at UC Davis) discussed this topic when he addressed tank mixes of Alion and Matrix in his UC Weed Science Blog article (linked here). My recent work with rimsulfuron on established johnsongrass also explored this subject (linked here). These prior discussions focused on rimsulfuron products as tank mix partners for pre-emergent applications, but I wanted test a broader range of products applied in February and March. This year’s walnut preemergent herbicide demonstration made some progress toward that goal.

    I will discuss my findings next, and at the end of this article I have included results tables. All products except one are currently labeled for use in walnut orchards, though with some restrictions on orchard age. The one unlabeled product in this study was Brake On!, manufactured by SePRO, currently pending registration in CA. This is not an exhaustive list, and the data provided here does not constitute a recommendation of any product.

    Trial design

    In 2025, I arranged my pre-emergent demonstration trial to evaluate individual products and tank mixes for weed control efficacy when applied in February and March. This trial was installed in the Loybas Hill region of Tehama County, in a 4-year-old walnut orchard with Tehama silt loam soil. A post-emergent mix of 2 qt/A Roundup Powermax 3 and 2 qt/A Rely 280 was added to every plot in February, and pre-emergent herbicides were applied either in the mix, or one month later in March. The tables at the end of this article show the full list of treatments and when they were applied. The first table represents weeds that were present at application, hairy fleabane and white clover. The second represents weeds that grew to be prominent in May and June, so their control depended on residual activity from my herbicide treatments lasting long into the summer.

    Results overview

    White Clover and Hairy Fleabane (Table 1): Both weeds were controlled by all three group 2 herbicides tested: Craze, Revolt, and Mission. Revolt was weaker on fleabane while Craze was weaker on clover and these differences also showed up in the tank mix treatments with both products applied with Prowl. February and March treatments with these three herbicides produced very similar results. The 12 fl oz/A rate of Chateau also effectively suppressed both species.

    Summer annual weeds (Table 2): The primary weeds in the categories recorded here were grass weeds (jungle rice and large crabgrass) and broadleaf weeds (prostrate knotweed, spurge, and pigweed). Many herbicides provided good control until June (3-4 months after treatment) but only Alion, Brake on! (not currently labeled for CA), and March-applied Mission maintained “good” control of broadleaves through July. Only Alion and Prowl maintained “good” control of grasses through July.

    Yellow Nutsedge (YNS; Table 2): Zeus was the best tested product for nutsedge control, but Craze also showed some effects in July by keeping nutsedge coverage low. Rimsulfuron products like Matrix and Revolt are also labeled for YNS control, but labels suggest sequential applications, and the application timings used in this trial may not have been ideal to target YNS with this product.

    Summary and cautions:

    This is a single trial only representing one weed population and one soil type, so results may vary by location. However, hopefully this demonstrates the importance of tank mixing to control emerged weeds as well as future emergence. Group 2 herbicides like Revolt, Mission, and Craze can provide good post-emergent control in addition to their pre-emergent activity. But be cautious, this herbicide group is notorious for herbicide resistance. Do not overuse this class of herbicides or you will likely start seeing weeds escaping your treatments.

    Look through the following tables if you are interested in seeing more information on efficacy in these trials. To see weed coverage data, view the report on the UCCE Tehama website here. Thanks to the California Walnut Commission for supporting this work. For any questions or additional information, contact Ryan Hill at 530-527-3101 or rjahill@ucanr.edu. — By Ryan Hill, UCCE Agronomy and Weed Science Advisor, Tehama County

    Weed control tables:

    Control was determined by calculating % reduction in weed coverage, relative to the plot with the worst infestation. Control is summarized by four categories. These categories may not represent each grower’s threshold of tolerance for weed control, but they can still provide relative comparisons between the products tested.

    Poor control is indicated by a “p”, representing control between 0 and 50%.

    Moderate control is indicted by an “m”, representing control between 50 and 70%.

    Good control is indicated by a “g” and highlighted light green, representing control between 70 and 90%.

    Excellent control is indicated by an “e” and highlighted dark green, representing control between 90 and 100%.

    Table 1: The effect of different pre-emergent herbicides on two weeds that were present at application, hairy fleabane and white clover.

    Table 2: The effect of different pre-emergent herbicides on weeds that germinated or sprouted in summer. Summer annual broadleaves included prostrate spurge, knotweed, and pigweed and summer annual grasses were primarily crabgrass and jungle rice.

  • California Walnut Board Announces Board Election Results

    The California Walnut Board is announcing a new Board of Directors, which has been certified by the U.S. Secretary of Agriculture. The Board of Directors consists of 10 growers and 8 handlers, which include three new individuals, who will serve a two-year term beginning Sept. 1, 2025, and ending Aug. 31, 2027:

    DISTRICT 1

    Grower Member: William D. Carriere, Glenn

    Grower Alternate: Jeff Gallagher, Rio Oso

    Grower Member: Ben Walsh, Orland

    Grower Alternate: Michael Petz, Tracy

    Handler Member: Jack Mariani, Winters

    Handler Alternate: John Aguiar, Winters

    Handler Member: Eric Heidman, Stockton

    Handler Alternate: Dick Wolf, Stockton

    DISTRICT 2

    Grower Member: Brent Barton, Escalon

    Grower Alternate: Daniel Bays, Westley (New)

    Grower Member: Greg Wiersma, Visalia

    Grower Alternate: Benjamin Crane, Merced

    Handler Member: Frank Guerra, Hollister

    Handler Alternate: Brock Middleton, Hughson

    Handler Member: Mike Poindexter, Selma

    Handler Alternate: Aaron Martella, Hughson (New)

    AT LARGE

    Grower Member: Michael Machado, Linden

    Grower Alternate: John Heier, Live Oak (New)

    “These newly elected board members bring valuable experience and fresh perspectives to the table,” said Robert Verloop, executive director of the California Walnut Board. “Importantly, they are not only committed to their own operations, but also to the broader success of the walnut industry. Their leadership will be critical as we work to create new opportunities for growth and ensure the long-term sustainability of the industry through our strategic plan developed in 2023, which aims to make California walnuts craved around the globe.”

    The board certification concludes the election process that began in February when nominations opened for board positions. Growers and Handlers across California received nomination petitions, followed by ballots in mid-April listing eligible candidates for their respective districts and statewide positions.

    The California Walnut Board members will help shape the future of the California walnut industry and guide its ambitious strategic plan, which focuses on six key priorities: product quality, global sales and marketing, innovation, sustainability, goal-oriented production and post-harvest research, and revitalizing the board and commission for industry cohesion.

    About the California Walnut Board

    The California Walnut Board (CWB) represents more than 3,700 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 CWB, established in 1948, promotes usage of walnuts in the United States through publicity and educational programs. The CWB also provides funding for walnut production, food safety and post-harvest research.

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

  • Good News For Hedgerows: No Effects On Food Safety In The Field

    Davis, Calif., (February 23, 2018) – Hedgerows enhance wildlife abundance and diversity around farmland without contributing to food safety problems in field crops, according to a new study published by a team of University of California researchers. The UC Agriculture and Natural Resources and UC Davis study documented that field edge plantings around farms are generally too narrow relative to the surrounding landscape to be a source of rodents and foodborne pathogens.

    “This study is particularly pertinent right now when FDA’s Food Safety Modernization Act (FSMA) is calling for farmers to co-manage wildlife and agriculture, instead of clear cutting wild habitat around their crops,” said co-author Rachael Long, UC Cooperative Extension farm advisor in the Sacramento Valley. “Our paper provides support for this ruling, showing that the presence of hedgerows does increase wildlife diversity, but does not increase wildlife intrusion into the fields and, more importantly, does not increase the prevalence of animals carrying foodborne pathogens.”

    This is good news for hedgerows, rows of shrubs, trees, grasses and flowers that are planted on field edges. The plants bordering crop fields provide habitat and floral resources for beneficial insects, such as bees and natural enemies, that help with pollination and biocontrol of pests in adjacent crops. Hedgerows also help enhance biodiversity – especially for insect-eating birds – help reduce wind and soil erosion, and protect water quality.

    The two-year study in Sacramento Valley walnut orchards and processing tomato fields was led by Long and Roger Baldwin, UC Cooperative Extension vertebrate pest control specialist at UC Davis, former graduate student Laurel Sellers, the Western Center for Food Safety at UC Davis’s Michele Jay-Russell, Xunde Lib and Edward R. Atwill, and Richard M. Engeman of USDA National Wildlife Research Center.

    The study, titled “Impact of field-edge habitat on mammalian wildlife abundance, distribution, and vectored foodborne pathogens in adjacent crops,” was published in the February 2018 Crop Protection (Sellers et al. 2018).

    Elsevier is providing 50 days of free access to this article. Anyone clicking on the following link before March 31, 2018, will be taken directly to the article on ScienceDirect. No signup or registration or fees are required. Simply click and read at https://authors.elsevier.com/c/1WXU~xPFYej~4.

    Winter migratory birds like to eat the lovely red berries of toyon.

    This journal article supports a growing body of literature suggesting that plantings along the edge of fields do not substantially attract wildlife species that intrude on fields and transfer foodborne pathogens. For example, in a 2015 study, UC Davis researchers found more food pathogens when wildlife habitat was reduced on farms. This may be attributed to the vegetation filtering pathogens, a better breakdown of pathogens in diverse environments, and that removing vegetation may not deter wildlife from entering farm fields.

    Relative to the larger crop acreage, hedgerows and similar field-edge habitats are generally too linear and small to serve as a significant source of rodents to damage nearby crops. However, cottontail rabbits favor hedgerows, and can sometimes cause damage to adjacent seedling crops.

    “Overall, we found risk of crop loss or contamination of foodborne pathogens in crops bordered by hedgerows wasn’t significant in our study in the Sacramento Valley, although potential damage could vary by the sta ge and type of crop and wildlife species present,” Long said. She will be presenting this work at the 28th Vertebrate Pest Control Conference, which will be held in Rohnert Park Feb. 26 to March 1.

    In its Standards for the Growing, Harvesting, Packing, and Holding of Produce for Human Consumption, the U.S. Food and Drug Administration says, “We continue to encourage the co-management of food safety, conservation, and environmental protection.”

    Hedgerows, the plants bordering this field of processing tomatoes, provide habitat and floral resources for beneficial insects that help pollinate crops and provide natural control of pests.

     

  • USDA California Crop/Weather Report

    Sacramento, Calif., (February 1, 2017) – The stopping of the Pineapple Express coupled with a retreat of the persistent upper-level trough that has been present over the western region for the last couple of months produced a week of warmer and drier conditions.

    Temperature highs were in the 10s to 40s in the mountains, 40s to 50s in the valley, 40s to 60s along the northern coast and deserts, and 70s to 80s along the southern coast. The temperature lows were in the -10s to 20s in the mountains, 20s to 30s in the valley, 20s to 40s in the desert, and 30s along the northern coast and 40s along the southern coast.

    Widespread showers fell on most of the state on Monday, with the heaviest rains seen in the San Diego area, where over one inch fell. Most other areas received less than a quarter of an inch of rain. Snow fell in the mountains, with the greatest accumulations in the 4-8 inch range in the area just southwest of Tahoe and also in parts of the southern Sierras. Tuesday and Wednesday continued to bring limited showers in certain areas, particularly the northern mountains and southern coasts. Thursday through Sunday saw no measurable precipitation at any reliable sites. Snow packs in the mountains continue to be in very good shape, maintaining cover through the week and likely increasing by 4-6 inches in the area around Tahoe.

    Continued rains have benefited the growth of already planted grains and field crops, but the rain has hindered ground preparations for continued planting. Low spots in some fields were showing stress from repeated standing water. Farmers in some areas have been encouraged to report crop losses due to flooding.

    Standing water and muddy conditions continued to hinder fieldwork for much of the state. Winter field work continued when conditions permitted. Deciduous fruit orchards continued to be pruned and brush shredded. Removal of orchards and vineyards continued in preparation for replanting with new varieties. Rain continued to slow navel orange and Satsuma mandarin harvest. Fungicide applications to citrus were made as conditions allowed.

    Some almond and walnut orchards were impacted by falling trees due to strong winds and saturated ground. Nut orchards continued to be pruned and brush shredded as weather conditions permitted.

    In San Joaquin County, conditions were drying out, which helped with standing water in the fields.  In Monterey County, heavy rains were welcomed, though the saturated ground restricted field access.  Growers began planting cole crops, as well as lettuces and greens.  In San Mateo County, the fields were still very wet and unworkable.  In Fresno County, the onions and garlic have germinated.

    Non-irrigated pasture and rangeland continued to green up due to this winter’s rain. Range was reported to be in excellent to good condition. Standing water and flooding continued to impact some valley pasture and dairies. Sheep grazed idle fields and dormant alfalfa fields. Where field conditions permitted bees were staged in preparation for the bloom season. Bee keepers continued to feed their hives to compensate for the lack of blooming vegetation.