California Ag Network

Tag: Orchard Management

  • September Orchard Tasks – Pistachios

    Pistachio harvest ended earlier than usual this year, but growers should not stop irrigating their orchards just yet. The early finish creates a longer post-harvest period before trees enter dormancy, making proper irrigation especially important.

    Research by Daniele Zaccaria, Mae Culumber and Anderson Safre of the University of California Cooperative Extension indicates that pistachio trees continue using water after the nuts have been removed. Although harvest is complete, evapotranspiration—the loss of water from the soil and through the trees’ leaves—continues until the trees become dormant.

    Because the post-harvest season will be longer this year, growers should continue monitoring their orchards’ water needs. Stopping irrigation too soon could place unnecessary stress on trees as they prepare for next season.

    However, the researchers suggest growers may be able to conserve water through carefully timed deficit irrigation. This practice involves applying less water than the orchard would normally use during selected periods. When managed properly, deficit irrigation may reduce water use by about 20% with little to no effect on the following year’s harvest.

    The key is timing. Growers should consider orchard conditions, soil moisture and the trees’ water needs before reducing irrigation. An early harvest does not mean water use has ended, and post-harvest management can play an important role in supporting the next crop.

    Read more about the research in the September issue of Pacific Nut Producer Magazine.

  • September Orchard Tasks – Almonds

    Although almond harvest may be wrapping up, the work needed to prepare orchards for next season has already begun. Post-harvest priorities include monitoring for disease, irrigating trees, pruning and managing pests.

    Brent Holtz with the University of California Cooperative Extension advises growers to watch for red leaf blotch and rust. Bright orange spots on leaves may indicate red leaf blotch, while orange and black spores can be signs of rust. This year’s warm March appears to have increased the severity of rust, making it important to avoid irrigation practices that keep orchards humid for extended periods.

    However, growers should not stop irrigating altogether. Water should be applied as soon as the harvested nuts are removed from the orchard floor. Dr. David Goldhamer, emeritus irrigation specialist with UC Davis, says almond trees can use up to 11 acre-inches of water after harvest if their leaves remain active. Proper post-harvest irrigation can also help move salt below the trees’ root zone.

    Growers can also begin pruning mature orchards immediately after harvest instead of waiting until dormancy. Pruning early gives wounds time to heal before rainfall, reducing the risk of fungal diseases. While studies indicate pruning does not significantly improve almond yields, it remains necessary to provide enough space for orchard equipment to pass between trees.

    Fall is also a good time to manage gophers, ground squirrels and mice. Baiting or fumigation can help control ground squirrels before they enter hibernation. Growers should also look for pieces of almond shells left in tree crotches, which may indicate mouse activity.

    For more information about post-harvest almond orchard management, read the full article in the September issue of Pacific Nut Producer Magazine.

  • 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

  • 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

  • 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.

  • Start off your Orchard Right with Minimal Weed Issues

    Special Thanks to This Video’s Sponsor

    With all the new tree nut orchards being planted in California, it’s important to remember that weed management is a priority, and it starts even before the planting process. Watch this brief interview with UCCE Farm Advisor Kurt Hembree as he explains, and read more in Pacific Nut Producer Magazine.

    Enjoy our Ag video news?  Be sure to let our sponsor Duarte Nursery know & thank them for their industry support!