Pacific Nut Producer Magazine

Tag: UCCE

  • How to Protect Your Almonds from Navel Orangeworm and Other Pests

    With spring weather arriving earlier, almond growers in California can expect an earlier influx of pests in their orchards — and to get started sooner on preventing them from harming their nut crops. According to UCCE Sacramento Valley Integrated Pest Management Supervisor Sudan Gyawaly, now is the time to watch out for things like navel orangeworm (NOW), peach twig borers, leaf-footed bugs and spider mites.

    Navel Orangeworm (NOW)

    Navel orangeworms (Amyelois transitella) are the most prominent pests in almond orchards. These moths lay their eggs on the shells after hull split, and the larvae burrow inside the shell, eating the nuts and sheltering inside. Signs of a NOW infestation in an orchard include:

    ·      Small, flat, oval-shaped eggs outside of almond hulls

    ·      Pinhole-sized holes in almond hulls

    ·      Hulls that are oily in appearance

    ·      Fungal infections of nuts

    ·      Extensive webbing inside the hulls

    ·      Partially eaten nuts

    ·      Larvae that are white to pink in color, with crescent marks behind the head

    Navel orangeworm damage to an almond. Photo by Matthew Malcolm

    To manage NOW in your orchards, be sure to continuously monitor male flight activity by using pheromone traps. Also continue to monitor NOW egg traps to establish a spring biofix (the first spring flight, which acts as the starting date for calculating growing degree days), to help you predict the timing of their later flights. The first flight usually occurs from late March through April, but earlier times are possible, depending on the weather.

    According to UC IPM, prevention is key to avoiding infestation. This includes removing all mummy nuts by the start of February. To eliminate existing NOW populations:

    ·      Establish a biofix

    ·      Hang pheromone dispensers in the trees to disrupt mating

    ·      Assess trap activity and begin spraying at hull split.  Apply pesticides at night and early morning for optimal results

    ·      Harvest and clean up as early as possible

    ·      Remove mummy nuts by March 15 of the next year.  Mow or disk mummies on the ground.

    Peach Twig Borer

    While less of a concern in mature orchards, peach twig borer — also a moth — can still be a menace for almond growers in younger fields by causing primary scaffold damage. Begin monitoring pheromone traps in April to establish a biofix and decide if a spray is necessary in May.  Consult with your pest control adviser if you are unsure.

    Leaf-Footed Bugs

    Stink bugs and leaf-footed bugs are especially troublesome after a warm winter. Leaf-footed bugs can be trickier to spot.  UC IPM lists the tell-tale signs of an infestation in your orchard as:

    ·      Gummy nuts — nuts with exudates on the outside of the hull — a signature warning

    ·      Nuts that have dropped prematurely

    ·      Black spots on kernels and wrinkled, misshapen nutmeat from adult feeding

    ·      Withered and aborted shells from bugs feeding on premature nuts

    Leaf-footed bug

    Stink bugs cause similar damage, but this is usually around May or June. Leaf-footed bug management can vary from orchard to orchard, depending on history and severity. Gyawaly advises basing spray decisions on this history plus on damage risk associated with seasonal conditions. Consult with your pest control adviser if you are unsure.

    Spider Mites

    Typically found in the lower parts of the canopy, spider mites may also come out earlier and in greater numbers with warmer weather. Their presence should be monitored once every two weeks.  For this pest, beneficial arthropods that prey on spider mites may be one of your orchard’s best friends. These species include:

    ·      Western predatory mites

    ·      Spider mite destroyers

    ·      Sixspotted thrips

    ·      Pirate bugs

    By monitoring and addressing mite and insect pests in the spring, the pest populations can be kept under control to ensure a large, high-quality almond harvest.

    Watch this interview on Navel Orangeworm: Video Interview

  • Groundwater Markets Tested in Mojave Basin

    As growers navigate SGMA, different avenues are being explored for access to the needed water for crops, including groundwater markets. This has been experimented with in the Mojave Basin, resulting in stabilized implementation  and aggregate gains, but also a consolidation of water rights. At the World Ag Expo, UC Cooperative Extension Associate Professor Ellen Bruno discussed the findings on groundwater markets with Matthew Malcolm at California Ag Network. Watch this quick video and read more in California Fruit & Vegetable Magazine.

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

  • 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.

  • Variety and Neighboring Crops are Predictors of Leaffooted Bug Risk in Almond

    Leaffooted bug is a sporadic pest in almond, but damage can be significant in years when pest pressure is high. The pest may evade early detection by growers and PCAs because it overwinters as adults in vegetation outside of the orchard and tends to colonize the upper tree canopy, rendering it generally out of sight. As a result, pest pressure is often realized after damage has occurred. The damage may vary considerably between almond varieties, adding yet another challenge for diagnosis.

    In Tulare County, heavy leaffooted bug damage was observed in May 2025 in almond orchards surrounded by citrus.  Adult leaffooted bugs (Figure 1A) overwintered in the citrus and then entered the neighboring almond orchards in March and April. By early May, symptoms of infestation included extensive nut drop (Figure 2A) and gummosis on the nuts (Figure 2B). Although the adults were not observed in the orchard, the pest was identified based on the observation of the characteristic egg strands of leaffooted bug (Figure 1B). In orchards with Nonpariel and Aldrich, both varieties were affected; however, the nut drop was more extensive in Aldrich than Nonpareil (Figure 2A).

    The full impact of the pest may not be realized until harvest because the quality of affected nuts remaining on the tree may also be compromised, thus reducing crop value. Nuts that are stung in late April to early July can be severely shriveled, have sunken lesions, or a brown spot depending on how developed the kernel was prior to feeding (Fig. 3, row 2-5).  These nuts stay in the tree, are harvested, and can significantly increase the percentage of nuts classified as inedible during nut quality assessments.  When examining a library sample of damaged kernels at harvest, nuts damaged by leaffooted bug fall into the same category as stink bug damage, as kernels damaged by these two pests are indistinguishable.

    In 2007, UCCE Kern County Farm Advisors David Haviland and Mario Viveros had the opportunity to evaluate the relative susceptibility of 15 almond varieties to leaffooted bug damage. That year, leaffooted bug invaded a Kern County variety trial research block that included 15 varieties planted in replicated, randomized blocks. This unique situation allowed for unbiased evaluation of the performance of varieties under equivalent pest pressure. Results indicated that the average number of aborted nuts per tree ranged from 0 to 33% of the total crop. Additionally, at harvest, the estimated rejects from leaffooted bug damage ranged from 0 to 30% of the harvested yield. Researchers also noted that crop loss varied by variety, with Fritz exhibiting the highest crop loss at 63%, followed by Sonora, Aldrich, Livingston, Monterey and Carmel.  The other varieties in the block had 3% or less total damage from the pest.

    The underlying basis for the differential susceptibility of almond varieties to leaffooted bug is unknown. Damage does not appear to be related to harvest date or shell hardness at harvest. Other factors such as plant volatiles, hull thickness, or shell hardness in April and May when the bugs are present may play a role in varietal susceptibility. Haviland and Viveros also noted that varietal susceptibility is somewhat relative, explaining that Wood Colony exhibited low susceptibility to leaffooted bug in the research plot, but significant damage was reported on Wood Colony in commercial orchards when combined with less susceptible varieties (ie. Nonpariel and Carmel).  These observations indicate that leaffooted bug prefers certain varieties, but in the absence of a preferred variety, the pest will remain in the orchard and feed on the most preferable variety of the less-preferred varieties present in the orchard.

    The 2025 observations in Tulare County, taken in consideration with the 2007 data from the UCCE variety trial suggest that the best way to monitor leaffooted bug is to focus attention on the most susceptible variety in the field. Gummosis and nut drop in the most susceptible variety will serve as an indicator of pest pressure in a given orchard. Growers with Fritz, Sonora, Aldrich, and Livingston should be extra vigilant in monitoring pest pressure.  Haviland and Viveros note that orchards composed of relatively unsusceptible varieties will have characteristically lower risk of leaffooted bug damage. Additionally, growers and PCAs should consider pest pressure from surrounding orchards and landscape plants that may serve as overwintering sites for the adults, thus contributing to the cryptic nature of the pest.

    Management programs for leaffooted bug consist of monitoring for the pest and spraying primarily with pyrethroids, when needed. Pest management guidelines for leaffooted bug and other pests can be found at www.ipm.ucanr.edu and reports of Almond Board of California-sponsored research can be found at https://www.almonds.com/research-database. — By Elizabeth Fichtner, UCCE Farm Advisor, Tulare County, and David Haviland, UCCE Entomology Advisor, Kern County

    Figure 2. Aborted nuts were prevalent on Aldrich, but the neighboring Nonpareil exhibited minimal damage (A). Gummosis and egg strands on aborted nuts indicated leaffooted bug damage (B).

    Figure 3. Leaffooted bug predation affects the quality of nuts remaining on the tree. Unaffected nuts are represented in row 1; affected nuts of varying quality are represented in rows 2-5.

    Figure 1. Leaffooted bug adults (A) are difficult to scout. Pest pressure is evident by the gummosis at feeding sites and the deposition of eggs in strands (B). Alternate hosts may harbor overwintering populations of leaffooted bug (C and D). Photos A, C, and D: W. Bentley.
    Figure 2. Aborted nuts were prevalent on Aldrich, but the neighboring Nonpareil exhibited minimal damage (A). Gummosis and egg strands on aborted nuts indicated leaffooted bug damage (B).
    Figure 3. Leaffooted bug predation affects the quality of nuts remaining on the tree. Unaffected nuts are represented in row 1; affected nuts of varying quality are represented in rows 2-5.

  • Can Whole Orchard Recycling Suppress Weed Establishment in New Orchards?

    Recent research has shown many potential benefits of utilizing whole orchard recycling (WOR) when removing an orchard. Instead of burning the wood produced in orchard removal, WOR involves chipping the wood from pulled trees and redistributing it back into the field using a chip or amendment spreader. This management technique has been mostly used in walnut orchards being followed by new walnut orchards. The conservation of the carbon in the wood benefits the soil by increasing nutrients available for the next crop, improving the soil’s water holding capacity and and enhancing microbial activity. After a recent evaluation of weed populations in a WOR trial in Yuba County, it appears that weed suppression in the first few years after orchard establishment at a WOR site may be yet another benefit to this practice.

    A WOR trial in Yuba County, led by UCCE Yuba-Sutter Farm Advisor Clarissa Reyes, was initiated by removing and chipping a mature walnut orchard at removal in late fall of 2023. The chips were spread at 60 tons/acre in winter 2023 in a grid design to allow comparison of orchard performance between areas with chips and areas without chips (control). RX1 rootstock trees were planted in April of 2024 and budded to Wolfskill walnuts in September 2024. In the first three months after orchard establishment, weed suppression was observed in the plots that had been covered in wood chips. Weed populations were surveyed in each plot in the orchard in August 2024.

    A representative three foot by twenty foot strip within the rows between two trees was evaluated for each plot within the trial. The percent of soil covered by weeds was estimated, and the dominant weed species were recorded. The plots treated with wood chips averaged 14% weed cover, while the control plots with no wood chips averaged 58% weed cover. This difference was significant and very visually apparent.

    In addition to difference in coverage of weeds, different species were observed in the chipped versus control plots. Almost all plots, regardless of treatment, had common knotweed (Polygonum arenastrum) and littleseed canarygrass (Phalaris minor). Control plots also had established populations of crabgrasses (Digitaria spp.), hairy fleabane (Conyza bonariensis) and fringed willowherb (Epilobium ciliatum). It is interesting that hairy fleabane, a particularly difficult weed to manage with known herbicide resistance, was suppressed in plots with chips. The possible mechanism of suppression for this particular weed could be physical, in that the seeds cannot germinate or seedlings are unable to break through the thick layer of mulched wood chips. Hairy fleabane has also been shown to be susceptible to allelopathy from juglone, produced by walnuts. There is no specific evidence indicating that the juglone in the soil from the wood chips is the control mechanism, but it may be worth evaluating in future trials.

    We expect that over time, the weed suppression will decrease and eventually there will be no difference between the chipped plots and the controls. However, reduced weed pressure in the critical first few years after orchard establishment may prove to be a valuable benefit to WOR. Annual weed surveys will continue in coming years of the Yuba County WOR trial. — By Becky Wheeler-Dykes, UCCE Glenn Orchard Systems & Weed Ecology Farm Advisor

  • Visual ID Guide to Help Manage New Almond Pest

    Since the first reports of a new almond pest – the carpophilus beetle (Carpophilus truncatus) – came in during fall 2023, it has become clear that the beetle is widely dispersed across the San Joaquin Valley.

    “My lab has identified infestations from every county in the San Joaquin Valley; we have found infestations in both almonds and pistachios, and we will likely find infestations in walnuts this fall,” said Houston Wilson, a University of California Cooperative Extension entomology specialist at UC Riverside. The California Department of Food and Agriculture has confirmed the beetle’s presence in Stanislaus, Merced, Madera and Kings counties.

    Historically a major threat to almond production in Australia, the beetle – as larvae and adults – feeds directly on the nut kernel. In California, some almond growers have lost 10 to 15% of their yield – a “significant economic loss,” according to Jhalendra Rijal, University of California integrated pest management (IPM) advisor for the region. Given the prominence of almonds as a commodity, even a 1% overall reduction statewide represents an approximately $70 million loss.

    “This year there has been a lot more reports from PCAs [pest control advisers]; they’re sending me the pictures of the damage and beetles,” said Rijal, noting that the increase is likely due to greater awareness of the pest.

    To help almond growers identify the carpophilus beetle and develop management plans, Rijal, Wilson and their IPM colleagues have put together a visual ID guide for the beetle and the damage it causes, as well as telltale signs of navel orangeworm (Amyelois transitella) and ant damage. In particular, the experts would like PCAs and growers to differentiate between the carpophilus beetle and navel orangeworm, another key pest in almonds.

    “Even though their way of causing damage looks more or less similar, we’re dealing with two different types of insects,” Rijal explained. “One is a Lepidoptera moth [navel orangeworm], and the other one is a beetle – many of the management practices and biological controls would be different for these two different things.”

    TOP: Both carpophilus beetle adults and larvae feed on the kernel and cause damage characterized by fine powdery frass and nutmeat, a white-creamy color with some webbing. Often, large numbers (more than 10) of adult and larvae are found per nut. BOTTOM: Navel orangeworm larvae cause damage characterized by thicker frass and silky webbing entangled with a darker, brownish appearance. Only larvae are present at harvest, usually 1 to 3 larvae per nut. Photos by UCCE Stanislaus IPM team

    To control carpophilus beetle, ‘sanitize, sanitize, sanitize’

    One crucial cultural practice for managing both pests, however, is destroying the remnant “mummy” nuts – the nuts that remain in the orchard postharvest. They serve as overwintering habitat for the carpophilus beetle, as well as its sustenance for the next generation of beetles in spring.

    “The best way to manage this pest is to do the orchard hygiene – continuing the winter sanitation, destroying the nuts that are on the ground and on the tree and on the berms,” Rijal said.

    Based on observations in Australia and locally, carpophilus beetles tend to rely more on mummies on the ground, whereas navel orangeworm generally favors mummies in the tree canopy. Correctly identifying the pest – with help from the new ID guide – enables growers to better target and prioritize their management efforts, Rijal said.

    “What we are strongly emphasizing is that growers need to sanitize, sanitize, sanitize to control both pests,” Wilson added.

    Correct identification of the pest would also prevent unnecessary application of insecticides, as those used for controlling Lepidoptera such as navel orangeworm would be largely ineffective on the beetle.

    Indeed, another insight shared by Australian experts is that the carpophilus beetle cannot be controlled just by insecticide.

    “Insecticides are not very efficient, given the cryptic nature of these beetles; exposing these beetles to the insecticide is very hard,” said Rijal, noting that the beetle spends most of its life cycle protected inside the nut.

    Reporting carpophilus beetle infestation helps researchers

    Mature larva of navel orangeworm (NOW) is 3 to 4 times larger than carpophilus beetle (CB) mature larva. Photo by Jhalendra Rijal

    This harvest season, Rijal advises almond growers to harvest as efficiently as possible, to minimize the number of mummies that need to be cleaned up. And because signs of damage (like damaged hulls and frass) are most obvious during harvest time, Rijal said growers should review the new guide, using the photos and other resources to help identify potential pests.

    If the grower or PCA suspects a carpophilus beetle infestation, they should contact the UCCE farm advisor in their area.

    Scientists are looking to expand their knowledge about this relatively new pest to California. In the coming weeks, for example, researchers are planning to survey for the carpophilus beetle in the Sacramento Valley.

    “Technically it has not been found there, but we suspect that we’ll find it this fall when we go looking for it,” Wilson said.

    Researchers are also collecting samples from infested orchards to better understand the biology of the species, as well as how it progresses through and responds to seasonal and climactic changes. In addition, they are analyzing data from a trial study of an insecticide that might be used as a supplemental control measure.

    “This is our first full season dealing with this insect, and there are still many things we need to understand,” Rijal said. “We are continuing our research efforts on all fronts.” — By Michael Hsu, UCANR

  • Efficacy of a Hull Split Spray vs. Sanitation for NOW Control

    Navel orangeworm (NOW) is most effectively controlled with the cultural practice of winter sanitation. Winter shaking almond trees to remove mummy nuts has proven to decrease next year’s NOW damage better than any other approach. The reason for this is clear. NOW overwinters as larvae in mummy nuts left in the tree after harvest and it is in these nuts the population carries over into the next season. Adult moths emerge in spring, mate, and lay eggs on mummies that are still in the trees as the females can’t find the new crop nuts until hull split. The second generation will then put direct pressure on the new crop nuts at hull split and the third generation will chew the nuts up during the harvest period.

    The way almond prices have been going recently, there’s no doubt that everyone is going to have to spend dollars as wisely as possible for the foreseeable future. Although cleaning the trees of mummies during the winter isn’t cheap, it is the method of NOW control where you clearly get the most bang for the buck spent. We’re really playing a numbers game here, and this is one practice that is stacked in our favor by the biology of this pest.

    For example, let’s assume a potential of 50 mummies per tree and 30 of them each have 1 NOW larvae. Half of those are female, and each female lays approximately 85 eggs. At harvest in late July we’re into the third generation, and for arguments sake let’s assume there’s no natural mortality.

    Look at what could theoretically happen to the worm population in one Nonpareil tree with 30 infested over-wintering mummies and no control:

    • 1st generation: 15 females x 85 eggs/female = 1,275 larvae
    • 2nd generation: 1,275/2 (half female) x 85 eggs = 54,188 larvae
    • 3rd generation: 54,188/2 x 85 = 2,302,990 larvae per tree at harvest!!!
                        (Thankfully, there IS natural mortality or else we’d be knee deep in worms!)
    Now, look at the impact of a hull split spray aimed at the second NOW generation. We know that sprays give at best about 60 percent control. This reduces the population but is not nearly as good as sanitation as you will see.
    • 2nd generation: 54,188 larvae x 40% survival after the spray = 21,675 larvae
    • 3rd generation: 21,675/2 x 85 = 921,196 larvae per tree to attack the crop at harvest.
    Now, look at what sanitation does in comparison. Start with the same 30 infested mummies per tree, then winter clean down to 2 mummies per tree. One is female, one is male.
    • 1st generation: 1 female x 85 eggs/female = 85 larvae
    • 2nd generation: 85/2 (half female) x 85 eggs = 3,613 larvae
    • 3rd generation: 3,613 larvae/2 x 85 = 153,531 larvae per tree at harvest.

    (If you can beat the 3rd generation by an early harvest you’re even further ahead.)

    So, a hull split spray reduced the worm population by 60 percent, but sanitation by itself, without spraying, reduced the population by 94 percent! When more NOW larvae make it through the winter, more egg laying will occur next season regardless of what else you do. In relation to the number of mummies left in the tree, expensive chemical treatments next season will only slow the rate of worm damage increase.

    If you have scarce dollars to spend on NOW control, spend them this winter when they will do the most good in a sanitation program. If the entire neighborhood works at this, the positive effect will be multiplied many times over for everyone. If you’ve got neighbors that don’t seem to get it, cleaning your orchard will still be a tremendous help to you. If you have no mummies, the first generation in the spring won’t be able to build up and establish a population in your orchard. You’ll benefit since they’ll have to fly in from the neighbors after hull split before they can begin to hurt your crop.

    Be sure to finish the job by destroying the infested nuts once they’re on the ground. Mow and shred the mummies before March 1st so NOW moths don’t have a chance to emerge. When you’re enjoying mowing during bloom in the spring, take personal satisfaction in seeing the chips and pieces of almond fragments and mangled worm parts fly out from under your mower! — By Joseph Connell, UCCE Farm Advisor Emeritus, Butte County

  • 2023-2024 Winter Chill, Dormancy & Walnut Management Update

    Walnuts are one of the highest chill requirement tree crops in California. Though it’s easy to forget given the luxuriously high amounts of chill last year, multiple recent winters have fallen short of the chill accumulation needed for a tight, economical walnut bloom (e.g. 2014, 2015, 2020). Inadequate winter chill accumulation can result in delayed budbreak, scattered or prolonged budbreak and buds on southern sides of branches never opening. Prolonged bloom can result in a wider variety in nut sizes, more small nuts, and multiple shakes, while also complicating timing of control measures for blight or husk split pests. In the next 20-40 years, Central Valley walnut orchards will get 14-20% less winter chill than in the 1950s when many of our grandparents were farming. Anecdotal experience suggests the chilling requirement for ‘Chandler’ is around 60-65 chill portions as quantified by the Dynamic Model. Given decreased chill projections it is likely that currently planted ‘Chandler’ orchards will not meet their chilling requirement in at least one out of ten years in most of the Central Valley in the coming decades, if left to their own devices. While we wait for high quality lower chill varieties to develop, how can walnut growers manage the chilling requirements of the orchards in the ground now? This has been the topic of many recent years of UC research with funding from the California Walnut Board and the California Department of Food and Agriculture.

    Looking at a sampling of four CIMIS weather stations using the UC Fruit & Nut Center chill calculator tool, on average the Sacramento Valley has accumulated 41 chill portions to date (written January 14th). This is about 20% below last year, and more in keeping with the winter of 2019-2020. While 2019-2020 was a low chill accumulation winter, that was due in large part to a fairly warm February. Thus, it’s too early to say if this is a year in which dormancy breaking treatments would be beneficial. Keep an eye on the UC Fruit & Nut Center’s chill calculator. Nonetheless, it’s good to be aware for future winters that there are options in the toolbox.

    For three winters, we have been studying the impact of a number of dormancy breaking treatments to give growers tools to deal with low chill winters (see here for more detail on previous years). Rather than wait for low chill years to come along, we’ve created warm winter conditions in large, open-top chambers that we’ve built around mature Chandler trees at the UC Davis campus. These trees were coupled with unheated trees that got sufficient winter chill. Approximately 30-40 days before (what we hoped would be) budbreak, dormancy breaking treatments were applied to different scaffolds in each tree. We then monitored budbreak over many weeks to quantify timing of 50% budbreak, the duration of budbreak and the percent of buds that opened on a scaffold.

    Over the course of three years, we’ve tested hydrogen cyanamide, often marketed as Dormex®, a blend of nitrogen compounds marketed as Erger®, an analogue of the plant hormone cytokinin, marketed as Mocksi®, and calcium ammonium nitrate (CAN-17), all of which were compared with a water control. Dormex is the only one of these products currently labeled for use as a dormancy breaker in walnuts (see label for more use details). Erger and CAN-17 are labeled as fertilizers. Over the last two years (2021 and 2022), we found that at least in terms of budbreak timing, it appears Dormex at 2% and 4% and CAN-17 at 20% could prompt heated scaffolds to behave like they had received enough chill, whereas Erger at 6% only partially compensates for lack of winter chill. Dormex at 4% moved timing even earlier than the sufficiently chilled control, whereas Erger moved the timing but only about halfway between the timing of the heated control and the sufficiently chilled control. No effect was seen using Mocksi over two years.

    This previous winter-spring, we put Dormex at 2% and 4% head-to-head. Given that last year was a very high chill winter, it was hard to force insufficient chill accumulation, even with our heated tents. Ambient trees accumulated 78-82 chill portions, while heated trees accumulated 10-12% less, 69-74 chill portions. Both Dormex at 2% and 4% moved terminal and lateral budbreak timing on the heated trees to similar values as seen in the unheated control, in essence compensating for the chill difference. Dormex at 2% also increased the percent of buds that opened, to values as high (lateral buds) or higher (terminal buds) than the unheated control scaffolds. Budbreak percent was not different between Dormex at 4% and the water control within heated or unheated trees. In other words, under these conditions of 69-74 chill portions, it would not have been beneficial to use Dormex at a rate higher than 2%. However, even given this range of chill accumulation, which is considered sufficient, 2% Dormex increased lateral budbreak from 29% to 42% and terminal budbreak from 89% to 98%. That said, in unheated trees, which accumulated 78-82 chill portions, there was no significant increase in budbreak from Dormex use at either rate.

    With generous collaboration from two grower hosts, we also compared Dormex at both 2% and 4% and CAN-17 last year at a field scale, to be able to collect yield data, in addition to budbreak data. At one healthy orchard just a few years into its prime yielding years (10th leaf) near Glenn County, where 73 chill portions accumulated (similar to heated trees on campus), we saw the same change in budbreak timing (3 days earlier) across each treatment when compared to no treatment. This did not lead to significant differences in yield, contrary to what the increased percentage of budbreak in the campus heated tented trees might have led us to expect. Yields ranged on average from 6,240-6,690 lb per acre across treatments. Across size quality measurements (percent jumbos, large, average nut weight, edible yield), nuts from the Dormex treatments were not significantly different from the control, though relative to the control nuts, the CAN-17 treatment had a lower average percentage of large and jumbo nuts (52% v. 64%) and lower average weight (9.15 g v. 10.09 g). There were no differences in color quality as measured by reflected light index (RLI) among any of the treatments.

    At the Chandler orchard at the Nickels Soils Lab, where 82 chill portions were accumulated (similar to unheated trees on campus), there was a small but significant change in timing of budbreak in each treatment relative to the control (3 days). Surprisingly, however, there was also an increase in yield in the 4% Dormex treatments relative to the control, yielding on average more than 1,400 lb more per acre (5,216 lb vs. 6,857 lb). The average yields in the Dormex at 2% treatment and the CAN-17 treatment were also numerically higher than the control (1,019 lb higher and 719 lb higher, respectively), but there was a great deal of variability in different replicates, making it difficult to statistics to decipher if yield differences can be attributed to the treatments. There were no differences between any of the treatments and the control treatment across size quality measurements (percent jumbos, large, average nut weight, edible yield) or color quality (RLI).

    It is perilous to draw conclusions about dormancy treatment efficacy at a field scale based on one high chill year’s data. The difference in yield effects at the Glenn County orchard and Nickels Soils Lab is intriguing. The Nickels site is an older orchard at a tighter spacing, suffering from significant limb dieback from shading coupled with Botryosphaeria infections. One possible explanation for the yield difference would be that the Nickels site benefitted from treatments that encouraged additional budbreak, whereas at the healthy, high yielding Glenn County orchard there was already sufficient budbreak without intervention. Knowing that June drop generally reduces cropload, it’d make sense that increased budbreak, as we saw in the campus trees with 2% Dormex, would not necessarily lead to increased yield. Given high chill accumulation in healthy orchards, dormancy breaking treatments are unlikely to pay for themselves at current walnut prices. If chill accumulation is lower than ~60 chill portions, our heated tent data indicates they may pay for themselves, but we’ll need yield data at production scale to know for sure. The Nickels results point to the possibility that dormancy breaking treatments may be of use in orchards with limb dieback. At the same time, we need to be cautious to watch for swings in yield this coming year that may result from over-taxing the already struggling trees. Particularly given how tight walnut budgets are these days, I’d wait for more data before trying out this orchard-renewal strategy at a large scale if I were a grower.

    We’ll continue this project with funding from the California Department of Food and Agriculture to improve understanding of ideal rates and timings, and the physiological response to these treatments inside the trees. Stay tuned! — By Katherine Jarvis-Shean, Orchard Systems Advisor UCCE Sacramento-Solano-Yolo

  • Preventing Bacterial Blast Damage in Almond This Year

    In 2023, the cold, wet weather during bloom and leaf-out resulted in bacterial blast damage in many Sacramento Valley almond orchards. If conditions this year are cold and wet during bloom, we may see a recurrence of blast: make a plan now to keep blast damage to a minimum.

    The Bottom Line:

    • Bacterial blast can be a problem when cold, wet conditions coincide with bloom or leaf-out.
    • Copper resistance is common in the pathogen: spraying copper is ineffective for preventing blast in many orchards.
    • Frost protection is the most economical prevention option and will help prevent damage from both frost and bacterial blast.
    • The antibiotic kasugamycin (Kasumin®) is effective for preventing blast when applied up to 7 days before cold, wet weather. It has received approval for availability this year under an emergency exemption registration (Section 18) but is not currently labeled for almond under a full registration (Section 3).The Details:

      Pseudomonas syringae pv. syringae (Pseudomonas) is a bacterium which can infect all aboveground parts of an almond tree. If leaves, flowers, or spurs are infected, the resulting disease is bacterial blast. Pseudomonas is ubiquitous in orchards, so bacterial blast is likely to develop whenever environmental conditions are cold and wet, which favors this disease. Pseudomonas is spread by water hitting the trees, either from rain or sprinklers. If this wetting occurs at the same time as frost damage, Pseudomonas can enter the tree through cells damaged by freezing. Trees are especially susceptible to frost damage during bloom and leaf-out, when tender new growth is exposed to cold temperatures.

      Preventing infection by Pseudomonas is the only way to control bacterial blast. Frost protection in an orchard is your best defense and your most inexpensive prevention strategy: if the trees are not damaged by frost, Pseudomonas will not be able to enter the tree to cause disease. As a second line of defense, research has shown that kasugamycin (Kasumin®) is effective for preventing bacterial blast when applied no more than 7 days before cold, wet weather. Note that kasugamycin is currently not labeled for use in almond, but has become available this season due to a Section 18 exemption. If the weather warrants treatment, kasugamycin can be used as a preventative spray up to two times during bloom. For this spray, complete coverage is crucial for control: all tender new growth must be covered in a protective layer of the antibiotic for it to be effective. Any tissue left uncovered will be unprotected.

      What about copper? Current work by UC researchers shows that copper-resistance is common in Pseudomonas throughout the state. Many of the orchards heavily affected by blast in 2023 received multiple dormant sprays containing copper. In some cases, mixing mancozeb with copper may provide some level of control, but research shows that this mixture is not as effective as kasugamycin and the copper can cause phytotoxicity. — By Jaime Ott, UCCE Tehama, Shasta, Glenn, and Butte Counties

      For more information on bacterial blast, check out these articles at sacvalleyorchards.com

      Bacterial blast/canker: What do we know? – an update on the factors predisposing orchards to damage by bacterial blast, and more details about control strategies for bacterial blast

      Bacterial Blast and Canker – a good description of the various symptoms seen with bacterial blast

  • 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