California Ag Network

Tag: UCCE

  • New Avocado Study Outlines Costs & Returns of High-Density Plantings

    Growers considering producing avocados in San Diego County with high-density plantings now have help to determine the economic feasibility. A new study on the costs and returns of establishing and producing avocados in San Diego County has been released by UC Agriculture and Natural Resources’ Cooperative Extension, UC Agricultural Issues Center and the UC Davis Department of Agricultural and Resource Economics.

    A worker prunes weak tree branches to improve sunlight penetration in a high-density avocado orchard.

    Avocado has been one of the prominent crops produced in Southern California since the early 1950s. California avocado production peaked in 1987-88 with about 76,300 acres. San Diego had been the leading producer accounting for about 60% of the acreage.

    “Beginning in the early 1980s, there has been a continuous decline of acreage and production of avocados in San Diego County, said Etaferahu Takele, UC Cooperative Extension farm management advisor for Southern California and co-author of the study. “This is mainly because of the expansion of urban development that has increased the cost of producing the crop and especially the cost of water, reaching to up to $2,000 per acre feet in 2020.”

    The same amount of water was sufficient for the high-density avocados as it was for the traditional planting (Photo by Gary Bender).

    High-density planting increases profitability of avocado production given there is suitable land for high-density orchard development.

    Although the cost of water accounts for 44% of the total production cost in the high-density planting, the water cost is proportionally less than in the conventional planting of 145 trees per acre when distributed over a higher yield per acre, the authors write.

    Their cost analysis describes production operations for avocados planted at 430 trees per acre, with an expected life span of 40 years. The study includes a detailed summary of costs and returns and a profitability analysis of gross margin, economic profit and a break-even ranging analysis table, which shows profits over a range of prices and yields. Growers can identify their gross margin and returns to management based on their yield and prices received.

    UC Cooperative Extension advisor Gary Bender checks sunlight penetration in a high-density avocado orchard.

    Input and reviews were provided by a UC Cooperative Extension farm advisor and grower cooperators in San Diego County. The authors describe the assumptions used to identify current costs for avocado establishment and production, material inputs, cash and non-cash overhead.

    The new study, “Avocado Establishment and Production Costs and Profitability Analysis in High Density Planting, San Diego County-2020,” can be downloaded for free from the UC Davis Department of Agricultural and Resource Economics website at http://coststudies.ucdavis.edu and UCCE Riverside County Farm Management website at https://ucanr.edu/sites/Farm_Management/Costs_and_Returns. Sample cost of production studies for many other commodities are also available on the websites.

    For additional information or an explanation of the calculations used in the studies, refer to the “Assumptions” section of the report or contact Takele at (951) 683-6491 Ext. 243 or ettakele@ucanr.edu or Donald Stewart at the UC Agricultural Issues Center at destewart@ucdavis.edu. — By Pamela Kan-Rice, UCANR

  • Broccoli Rotations Lower Pathogen Populations and Reduce Disease Incidence of Verticillium Wilt

    In 1999, several UC researchers published foundational research in a paper titled, “Evaluation of broccoli residue incorporation into field soil for Verticillium wilt control in cauliflower.” Since this publication more than 20 years ago, many studies have further investigated this concept and many coastal growers, especially organic producers, have adopted broccoli rotations as a strategy for Verticillium wilt control. Today, typical implementation of this strategy is two broccoli plantings back to back prior to the crop for which Verticillium wilt suppression is desired. While California coastal vegetable production has been the framework for much of this work, the adaptability of this practice to the Sacramento Valley is very promising for management of Verticillium wilt in warm and cool season crops.

    Verticillium wilt is caused by the soilborne fungal pathogen Verticillium dahliae. Microsclerotia, the fungal inoculum that causes infection, dwell in the soil until root exudates stimulate germination and direct the fungal hyphae towards the root. In susceptible plants, infection occurs when hyphae enter the roots right behind the root tip, and continue growth into the water-conducting vascular tissue, the xylem. Once in the xylem, hyphal growth and sporulation can move the fungus into the upper plant tissue. Plant death triggers the fungus to a reproductive stage, prompting microsclerotia formation. When infected crop residue is incorporated into the soil, microsclerotia in the crop residue are incorporated, too. Management is particularly challenging because the pathogen host range is over 300 crops and the inoculum survive upwards of 13 years. To establish control of the pathogen, the key is to reduce inoculum—the number of microsclerotia, below levels damaging to susceptible crops.

    BROCCOLI SUPPRESSES VERTICILLIUM WILT AND DECREASES PATHOGEN PROPAGULES

    Broccoli is one of the few non-host vegetables and member of the Brassicaceae family. Bok choy, broccoli raab, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, and rapini are susceptible to V. dahliae, as are black mustard, Indian mustard, oilseed rape, and turnip. In broccoli, no infection to minor infection from V. dahliae has been observed. In the case of minor infections, the pathogen does not progress beyond the roots and microsclerotia formation in the roots is repressed. Apart from the importance of selecting a non-host as a rotation crop, the glucosinolate profile of broccoli, the secondary compounds responsible for the toxic effect, differs from other brassicaceous crops

    Following broccoli residue incorporation, research out of Japan demonstrated Verticillium wilt incidence of eggplant decreased by 53% compared to eggplant without broccoli rotation. In California Cauliflower production, disease incidence and severity were both reduced approximately 50% following broccoli residue treatments.

    Broccoli did not just decrease disease incidence, but decreased the amount of pathogen inoculum, showing promise for longer term management. In a California study, overall reduction in the number of propagules in V. dahliae-infested plots after two broccoli crops was approximately 94%, in contrast to the five-fold increase in the number of propagules after two cauliflower crops. These findings corroborate earlier studies showing reductions in the numbers of soilborne microsclerotia of V. dahliae and incidence of wilt on cauliflower that were comparable to reductions caused by chloropicrin and metham sodium treatments. Importantly, following broccoli rotations, microsclerotia continue to decline through-out the following cropping season and remain low during the following season. In contrast, propagules in soil fumigated with chloropicrin and metham sodium declined initially but later returned to pre-treatment levels by the end of the cropping season.

    MECHANISM OF SUPPRESSION

    Shetty et al. (2000) reported that the effects of broccoli in reducing microsclerotia and suppressing disease may be associated with the following mechanisms: production of volatile antifungal substances such as allyl-isothiocyanate (ITC) by broccoli residue, increase in antagonistic microorganisms, and degradation of microsclerotia melanin by ligninase/melaninase produced by soil microorganisms in the presence of broccoli lignin. ITCs are chemically similar to methylisothiocyanate, the active agent from the chemical fumigant metam sodium. Likely associated with the ability to generate these conditions, fresh broccoli residue was shown to be more suppressive than dry residue. During tissue decomposition, the glucosinolates in crucifer crops, the characteristic sulfur-containing constituents of the members of Brassicaceae responsible for their inherent pungent odor, break down to produce sulfides, isothiocyanates, thiocyanates, and nitriles that have either fungistatic or fungicidal properties. In addition to release of toxic compounds and microbial activity provided by broccoli residue, the plant may be serving as a ‘decoy’, ‘trap crop’ or ‘dead end host’, further driving population numbers down. As described earlier, some V. dahliae infection is observed in broccoli roots, but it does not result in microsclerotia formation. By stimulating inoculum germination and preventing fungal reproduction, the number of viable microsclerotia decrease in the soil.

    GROWER IMPLEMENTATION OF RESEARCH FINDINGS

    To facilitate greater adaptation of rotations with broccoli in other crops susceptible to V. dahliae, Bhat and Subbarao asked the question whether isolates of V. dahliae originating from different susceptible hosts could cause wilt on broccoli. They evaluated 15 different host isolates against multiple broccoli varieties. This included tomato, eggplant, bell pepper, lettuce, potato, watermelon and strawberry, and found that only isolates from cabbage and cauliflower were weakly pathogenic. Broccoli cultivars Baccus, Greenbelt, Parasol, Patriot, and Symphony showed resistance to Verticillium infection. This provides some evidence for the usefulness of this method in other cropping systems.

    Implementation of broccoli rotations for Verticillium wilt management is optimized when two successive broccoli crops are grown immediately prior to desired Verticillium wilt reduction. Higher amounts of glucosinolates, specifically glucobrassicin, are found in older plants. Research has reported a complete absence of glucobrassicin in broccoli seedlings, 50% of the total in immature heads (5-10 cm diameter) and the highest levels at fully developed Packman broccoli heads (15-20 cm diameter). These results suggest that glucobrassicin synthesis is active during later stages of broccoli development. Plants should be mowed and finely chopped in order to disrupt the plant cells as much as possible. The greatest reductions in microsclerotia occur at soil temperatures above 68°F, and most of this reduction occurs within 15-30 days of incorporation. Variation in efficacy of this method is attributed to multiple factors: fluctuation in climate and cultivation conditions, physical and chemical properties of the soil, soil microbial properties, the type of broccoli cultivar used, differences in pathogen density, and variance in the susceptibility of the following crop host. The types and amounts of glucosinolates vary with the crucifer species and determine the level of plant pathogen growth reduction.

    This practice could also have other potential benefits and drawbacks. Growers in California have observed for many years that where broccoli residues from processing plants are dumped onto a field, weed populations are reduced the following year. Thus, rotations with broccoli may have multiple pest management benefits. However, in recent years in the Sacramento Valley, crop damage from bagrada bug has been significant. Although these outbreaks have largely occurred in fall, outbreaks have occurred in the spring in this region. Members of the Brassicaceae family are the host plants for bagrada and under favorable environmental conditions would support this pest population.

    This management strategy is specific to Verticillium dahliae and is not transferrable to other soilborne pathogens such as Fusarium spp.. Because these two pathogens are common in the Sacramento Valley and above ground symptoms are similar, diagnosis is important. Contact me at any time for disease diagnostic support. All visits and sample analyses are provided free of charge.

    Thousands of microsclerotia, small, black propagules of V. dahliae, formed on susceptible crop residue and remained intact post residue incorporation (Photo by M. Lloyd).

    SUMMARY

    • Two broccoli plantings immediately prior to growing the verticillium-susceptible crop is recommended for best protection
    • Fresh broccoli residue has greater reduction in V. wilt than dry residue
    • Field tarping following fresh residue incorporation did not increase (or decrease) efficacy
    • Suppression of V. dahliae is specific to broccoli and not provided by other Brassicaceae crops.
    • V. dahliae isolates from 15 host crops, including tomato, eggplant, bell pepper, lettuce, potato, watermelon and strawberry, were effectively suppressed by 5 broccoli cultivars
    • The most significant reduction in V. dahliae occurs 15 days post-incorporation, and continues to decline over the season.
    • More mature broccoli plants have higher levels of volatile antifungal substances
    • The mechanisms of action are hypothesized to include: volatile antifungal compounds, changes in the soil microbial communities and serving as a ‘dead-end host’.
    • Broccoli has been shown to reduce pathogens causing Verticillium wilt and lettuce drop, but not other soilborne pathogens such as Fusarium spp. — By Margaret Gullette Lloyd, UCCE Small Farms Advisor

    SUGGESTED READING

    Koike S, Subbarao K. 2000. Broccoli residues can control Verticillium wilt of cauliflower. Calif Agr 54(3):30-33. https://doi.org/10.3733/ca.v054n03p30.

    http://calag.ucanr.edu/archive/?type=pdf&article=ca.v054n03p30

  • Transform (sulfoxaflor) Full Label Could be a Major Benefit for Alfalfa IPM

    The California Department of Pesticide Regulation is currently reviewing the use of Transform (sulfoxaflor) for insect pest management in alfalfa hay production. A decision on whether to register Transform with a label for use in California alfalfa is expected to occur by the end of 2020. The registration of Transform has been so far deferred due to concerns of potential impacts on pollinators. Transform currently has a full EPA label for use in alfalfa hay in all other states, but not in California. 

    This is something California alfalfa growers and PCAs should pay attention to, and consider weighing in.

    Why is this of interest? California, with its mild climate, supports a wide range of sucking insects, including an array of alfalfa pests including blue alfalfa aphid (BAA), pea aphid (PA), spotted alfalfa aphid (SAA), cowpea aphid (CPA), as well as whitefly and leafhoppers.

    Figure 1. Blue Alfalfa Aphid Damage, Nevada, 2020. Growers in other states are able to use Transform to control this damaging pest.

    There have been major insect pest outbreaks in alfalfa in recent years (see article “The Blue Alfalfa Aphid: A continuing problem” ). Growers have struggled to control these devastating pests, unfortunately often spraying multiple times with broad-spectrum insecticides in attempts to control their damage. The BAA especially has become more difficult to control.

    This is a problem for several reasons: 1) These hard-to-control infestations have been economically devastating to California growers, 2) growers often use broad-spectrum insecticides which have the unfortunate effect of damaging beneficial predator populations (which help to control remaining pests) – see ‘Natural Enemies are Important”, and 3) over-use of the same insecticides can lead to insecticide resistance (see blog). These lead to environmental problems (excessive pesticide use), insecticide resistance, as well as high costs and low production.

    Diverse Tools Needed. Targeted and effective, aphid-specific tools for alfalfa are critically needed by this industry, which is losing insecticides (e.g. see ‘The End of Chlorpyrifos’) and has seen pests become increasingly difficult to control. Transform would be a useful tool to address this need.

    Figure 2. Blue alfalfa aphid (left) and Cowpea aphid (right) are commonly seen in alfalfa fields. The blue aphid is particularly difficult to control.

    Our data suggest that Transform works well for managing serious sucking insects like aphids, whiteflies, and leafhoppers that cause significant yield and quality losses in alfalfa. BAA continues to be challenging to control with significant yield and quality losses occurring statewide (See Blog ‘I’ll be Back’ from April, 2020). Stubble fields that are just breaking dormancy late winter are the most at risk of stand and yield losses. Small, growing plants are vulnerable to the toxins that BAA inject during feeding.

    Statewide Label Needed. Transform currently has a Section 24c Special Local Needs (SLN) in California for Siskiyou, Lassen, Modoc, and Shasta Counties for helping to manage BAA and other aphid pests, with restrictions (applications must occur between 7pm and 7am OR when the temperature is below 50 F at the site of application).

    Alfalfa growers would greatly benefit from a statewide label for Transform in alfalfa, similar to what is in place in other states, especially for southern regions which have seen devastating aphid infestations. Transform would be a good tool to have in alfalfa because UC Cooperative Extension (UCCE) research has shown that:

    1)      In UCCE low desert trials, Transform can have better efficacy controlling BAA than Sivanto (flupyradifurone), another aphicide registered for use in alfalfa.

    2)      Transform is softer on beneficial insects than currently registered pyrethroids, organophosphates, and carbamate insecticides, helping to prevent secondary pest outbreaks and resurgence of pests.

    3)      Transform provides growers with a much-needed tool to control multiple pests during a single growing season, including whiteflies, aphids, and leafhoppers, which unfortunately may take multiple insecticide applications otherwise.

    Restrictions.  CA-DPR also needs to address the restrictions in the current 24c SLN because they are problematic for several reasons:

    1)      UCCE research shows that night time or early morning dew on the alfalfa foliage may interfere with the efficacy of Transform, resulting in a 30% reduction in efficacy. This is important since yield damage can occur from blue alfalfa in just a few days.

    2)      For warmer regions of the Central Valley and the Low Desert regions (Palo Verde and Imperial Valley), restricting applications to < 50oF is nearly impossible to meet because BAA is most problematic in March when temperatures are often above this.

    3)      Keep in mind that forage alfalfa harvested in spring (when aphids are most damaging) is largely harvested in the bud stage, not flowering, lessening the risk to pollinators, especially given a 7-day pre-harvest interval, which is typically well before flowering.

    4)      Night-time applications are more dangerous for applicators. Worker health and safety is improved for daytime applications.

    Summary

    A full label for Transform would be of benefit to farmers and would help reduce the over-use of broad spectrum insecticides that we have observed taking place in attempts to control large aphid infestations. We have observed farmers unfortunately spraying multiple times (e.g. a pesticide treadmill), when a more focused aphid control measure would be more effective, and protect beneficial insects. UCCE research has shown that Transform provides excellent control of piercing-sucking insects like aphids, whiteflies, and leafhoppers, and would contribute to a diversity of tools to manage insect pests in an integrated way. Transform (sulfoxaflor) is a selective insecticide that is relatively safe for important aphid predators such as lady beetles and lacewings and thus contributes to goals of IPM. — By Dan Putnam, Rachael Long, Michael Rethwisch & Ian Grettenberger, UC Cooperative Extension

  • UCCE Vegetable Crop Guru Burt Hoyle Passes

    Burton John Hoyle passed away in McKinleyville on Nov. 9, 2020, just weeks from reaching his 101st birthday.

    Burton (Burt) was born in Saranac Lake, NY, in 1919. He grew up in the Jamestown, New York, area. He graduated from high school in 1938 and spent several years pursuing odd jobs before starting college in 1941. He did not serve in WWII because of a childhood injury. In 1944, he graduated from the University of New Hampshire with a degree in horticulture.

    There was a war going on and jobs were scarce, so Burt applied to graduate schools. The University of California, Davis, wrote that classes were closed, but they did have a job opening in vegetable crops. After Burt got to Davis, classes soon resumed with the end of the war, and he graduated in 1946 with an M.S. in vegetable crops. That same year he also married True Dolson.

    As 1946 drew to a close, Burt took a job with the University of California Cooperative Extension system to pioneer the Agricultural Experimental Field Station in Tulelake, now known as the Intermountain Research and Extension Center (IREC). From 1947-1965 Burt’s research and work shaped many of the crops still grown in the Tulelake Basin today including potatoes, barley, peppermint and strawberries, according to a letter Rob Wilson, current Intermountain REC director, wrote to Burt for his 100th birthday.

    However, Burt’s big winner was the introduction of horseradish as a cash crop. In 1983, he was featured in an NBC nationally broadcast news show as the “Godfather of Horseradish.”

    Hoyle and wife True at Intermountain REC in 1947.

    In 1965, Burt relocated to Fresno where he worked as a vegetable crops specialist at the University of California’s West Side Station in Five Points. Two major publications from his many projects were A Guide to Commercial Vegetable Production (1970), Curley Top Identification Handbook (1977) [Curly top is a plant disease]. His work on “aggresizing” [a process for making the soil optimum for successful seed growth], for which he received a patent, led to widespread recognition in the agricultural research community.

    Burt and True were active in the First Presbyterian Church in Fresno. One of the ways they lived out their faith was by opening their home to many foreign students. Over a period of more than 10 years, they hosted a number of Chinese, African and Middle Eastern students. Their involvement with these students was a ministry as they helped them with practical matters, and also spent hours counseling them about their lives.

    Burt retired from UC ANR in 1983 and he and True relocated to Humboldt County. During the 1980s Burt enjoyed Rotary, his friends and taking pictures of beautiful Humboldt scenery. He traveled up and down the coast shooting pictures; then with his scanner and Adobe Photoshop, Burt explored the creative expressions of the visual, displaying some of his photos at local art shows. He and True were very involved with the Arcata Presbyterian Church and participated in many community activities. Burt and True also engaged in developing housing on land in Arcata, which True had inherited from her family.

    True Dolson Hoyle passed away in 2005, and Burt married MaryAlice Comstock in 2006. MaryAlice preceded Burt in death on Sept. 16, 2020. She was 91 years old.

    Burt was blessed by health, mental clarity and mobility throughout his life. He was known for his brilliant thinking and ever-present curiosity. During his final years, he was working on a book on statistical thinking and re-analyzing data from his field crop experiments he had collected more than 50 years ago. Even in his last days, his caretakers commented on his intellectual curiosity, his smile and sense of humor.

    He is survived by his three children, Joe and Glenn Hoyle and Pamela Lund, three grandchildren, Julie McGuffey, Karin Ballstadt and Dennis Hoyle, and 10 great-grandchildren.

    His three children remember the significant impact Burt had on their lives, but more importantly his love and concern for them, their families, and for the large number of people whom Burt influenced. — By Glenn C. Hoyle

    To read more about Hoyle’s work at IREC, see this 1964 California Agriculture article //ucanr.edu/sites/anrstaff/files/340045.pdf.

  • Walnut Replanting Considerations in a Lean Price Year

    When prices are lean walnut farming is tough business. Farm advisors are not economists or financial advisors. However, farm advisors can be useful in providing best practices for economically sustainable production. Two key economic decisions growers face are when to replant individual trees and when to remove and replant entire orchards.

    Learn from Dying Trees to Improve Management of the Whole Orchard:

    Former Advisor Carolyn DeBuse, and Emeritus Advisor Bill Krueger wrote about the need to pause before replanting, by asking why the tree died in the first place. Saturated soils and soil borne pathogens are common culprits for tree loss. It is important to carefully evaluate recently declining trees, particularly evaluating their root systems for a possible cause. Your pest control advisor or local farm advisor can help with this diagnosis. Can changes be made to reduce the chance of additional trees declining and increase the chance of success for replanted trees? For Phytophthora and nematodes, these changes are often genetic (i.e. replant rootstock selection) but may also include a chemical approach. However, the needed action is just as often cultural, whether it is adjusting irrigation set time to prevent ponding or installing stream-splitters to keep water off trunks.

    Water logging is a common cause of walnut tree decline: sacvalleyorchards.com/blog/walnuts- blog/yellowing-collapsing-walnut-trees-pt-1-water-logging. The Howard variety appears particularly sensitive to saturated soils: sacvalleyorchards.com/blog/walnuts-blog/yellowing-collapsing-walnut-trees- pt-2-yellowing-howard-problem. In addition to tracking saturated conditions with soil moisture monitoring, a key practice to not over-watering is irrigating only when demanded by the trees, as indicated through regular pressure chamber use. Learn more at: sacvalleyorchards.com/manuals/stem-water- potential.

    Tree Replanting Decisions:

    When a tree dies and is removed, there is always a question of whether to replant in that spot. The decision of whether to replant an individual tree is a gamble that the replant will become established and produce enough to offset its associated costs by the end of the orchard’s life. A decision that is an automatic “yes” early in the orchard’s life becomes more complicated as the orchard ages.

    The shading from surrounding trees, and the ensuing low probability of successful vigorous growth weighs against the desire to replant and establish lost production. DeBuse and Krueger noted that if the orchard floor has over 75% shade at midday, the chance of a successful replant is slim. However, UC Davis Walnut Specialist Bruce Lampinen believes that a successful replant is dubious in orchards with over 60% shading. If the decision to replant has been automatic for you, pause to consider the cost of an unsuccessful replant and first evaluate how much light is available to the new tree.

    After weighing the success of the replant and evaluating why the original tree died, if you do replant, follow the best practices to help nurture this investment. Root removal, possible spot fumigation, nursery product selection, and correct planting are the key steps. Of these, nursery product selection is a particularly critical step, if possible, tailor the choice of rootstock to the main source of tree loss (see rootstock table below). As part of nursery selection, choosing a bareroot over a potted tree is typically ideal because you are starting with a tree that is larger and easier to manage. Once the replant is in place, the tree stands little success without paying extra attention to the need to modify irrigation and fertilization. You can learn more in the excellent guide by DeBuse and Krueger at: sacvalleyorchards.com/walnuts/orchard-development/replanting-individual-trees.

    Orchard Replanting Decisions:

    In addition to a lack of available light, general orchard decline is a second major reason to rethink replanting individual trees. General orchard decline in old age, frequently the result of weak trees facing an onslaught of multiple pests and diseases (figure 1), means replants make little sense because of the short window remaining in the orchard’s life. Instead, the orchard should continue to be farmed without replants until it is no longer economically feasible to do so.

    Figure 1. An orchard facing general decline, with a high rate of tree loss. Extensive crown gall, trunk cankers, and high nematode counts all present in this orchard.

    Amidst lean prices, if this is the year that you slate an orchard for removal, there are several steps you should consider before removal. A critical initial step, just as with replanting individual missing trees, is to ask why the orchard is in decline, and if those problems may follow you into the next planting. In addition to assessing the risk of the replant problem, and the persistence of crown gall, a nematode sample taken while the current trees are still in the ground is a great start. You can learn more about nematode sampling at: growingthevalleypodcast.com/podcastfeed/2019/10/22/nem-sampling and result interpretation and the next steps for replanting amidst high lesion nematode counts at: sacvalleyorchards.com/walnuts/orchard- development/replanting-into-nematode-infested-soils.

    Building upon this initial diagnosis step, consider the following steps:

    1. Assess potential carry-over problems before harvest.

    2. Kill the roots of the old orchard. The established best practice for this is cutting down trees above ground during October and within 5 minutes painting the stump with Garlon3A, or a mixture of 1:3 mixture of Garlon3A and MorAct.

    3. Wait a full growing season before replanting walnuts. This is the step where there are a range of management choices, such as the decision to fumigate, the use of a spring-summer crop to dry down deep soil moisture, or even exploration of a new technique like anaerobic soil disinfestation.

      This is also the step, where you could consider whole orchard recycling (WOR), whereby the previous trees are chipped and incorporated back into the soil. In almonds, this has been successful both for the performance of the subsequent planting and for soil health. Problems and success with WOR in walnut have yet to be demonstrated, with only a single pilot demonstration of young second generation WOR trees to- date. Until we have data on the persistence of crown gall and lesion nematode in roots of a recycled orchard, this practice is not advised for orchards with heavy cases of these afflictions. You can learn more about WOR at orchardrecycling.ucdavis.edu. WOR is an expensive practice, however the practice is now recognized for potential financial support through the CDFA’s Healthy Soils Program: cdfa.ca.gov/oefi/healthysoils.

      1. Fumigate, if necessary. The choice of whether to fumigate is centered around the concerns of root lesion nematodes, the replant problem, and to a lesser extent crown gall when replanting walnut orchards. Specifically, if lesion nematode is present in the old orchard, nematicide (e.g. Telone) fumigation, in addition to all the other steps may be necessary to have a successful replant to walnut. Fumigation is expensive, however the carryover problems from the previous orchard can prove far more costly. Cost savings with fumigation can be achieved by opting for strip fumigation specifically mapped for the tree rows, instead of broadcast fumigation. Adequate fumigant distribution can be problematic especially on clay-type soils. To ensure a successful fumigation, it is critical to dry down the soil to 12% moisture for optimal fumigant efficacy.

      2. Replant on an appropriate rootstock. Consider the potential benefits of clonal Paradox rootstocks, particularly against nematodes (VX211) and Phytophthora (RX1). See detailed rootstock traits in the table below.

      Find more about orchard removal and replant steps at: sacvalleyorchards.com/walnuts/diseases/considerations-for-replanting-walnut-orchards. Finally, if you are removing and planting a new walnut orchard, a key document to have on hand when financially planning is the Sacramento Valley UC Walnut Cost Study, which can be found at: coststudies.ucdavis.edu/en/current/commodity/walnuts.

      Article By:

      -Luke Milliron, UCCE Orchards Advisor Butte, Glenn & Tehama Counties

      -Katherine Jarvis-Shean, Orchards Advisor Yolo, Solano & Sacramento Counties

  • California Must Become a Fire-Adapted Civilization, UCCE Expert Says

    The vast California acreage burned in 2020 and the protracted smoky skies should signal state residents and officials to adapt to a new reality, reported Ezra David Romero on Capital Public Radio. The 4 million acres of wildland burned this year isn’t unprecedented.

    Before 1800, 4.5 million or more burned every year in California, according to a UC Berkeley study.

    Tragic as they are, parts of the 2020 fires will bring some areas back to natural equilibrium. “Some areas are going to be hit really hard . . . and will have trouble recovering,” said Michael Jones, UCCE forestry advisor in Lake County. “But other areas will look phenomenal. They’ll look fantastic and they’ll do exactly what we want these systems to do.”

    However, the burns are unprecedented in California’s modern, highly populated times.

    “I don’t think that we can have another season like this without something fundamentally shifting,” he said “This is another indication of how we need to think differently about how we approach managing fire, and how we need to become more of a fire-adapted civilization.”

    It may be “a tough pill to swallow,” but Jones told Romero that smoky skies could become a year-long reality because of prescribed burns in cooler months and a prolonged wildfire season in the warmer months.

    “People are exhausted,” Jones said, “they’re scared and don’t understand this fundamental shift and change.”

    Jones says the current fire season should also force people to rethink where communities should be built. — By Jeannette Warnert, UC Cooperative Extension Communications Specialist

    UCCE forestry advisor Michael Jones.

  • Managing Root-Knot Nematodes in Crop Rotations

    A question came up about managing root-knot nematodes in processing tomato and lima bean rotations.  Root-knot nematodes are tiny worm-like soil dwelling pests that cause root galling on plant roots, resulting in significant yield and quality losses. Symptoms of severe root-knot infestations include patches of chlorotic, stunted, necrotic, or wilted plants. These nematodes also predispose plants to other soilborne pathogens that cause root rot and wilt diseases. For example, a bean variety resistant to infection by the Fusarium wilt pathogen will become susceptible to this disease if infected with root-knot nematodes.

    What is the link between nematodes in tomatoes and limas? Dr. Phil Roberts, Nematologist at UC Riverside shared the following response:

    There are several root-knot nematode species and they differ in their response to resistance in tomato and various bean crops. Most common in our Sacramento Valley area are Meloidogyne incognita and M. javanica. These nematodes are normally controlled by Mi-1 gene based resistant tomatoes, but there are resistance-breaking populations so that could be the reason for the infection on tomato (unless the tomatoes grown were not actually resistant). A further possibility is that the species is M. hapla, which is not controlled by the tomato resistance. M. hapla tends to induce smaller pearl-like galls on tomato roots and is not common in the Sacramento and northern San Joaquin Valleys.

    Root-knot Nematodes Causing Galling on Tomato Roots

    As to rotating with lima beans, limas are susceptible to these root-knot species but there are resistant varieties available. Beja Flor baby lima has strong root-knot resistance. It was bred to contain three resistance genes that do a good job of blocking M. incognita and M. javanica. It yields well with the caveat that Steve Temple (former UCCE legume specialist) used to remark that it is more Lygus bug susceptible than some varieties, so if a grower went with UC Beja Flor they would need to keep up on the Lygus management. UC Luna baby lima has no root knot resistance. Other lines carrying M. incognita (but not M. javanica) resistance are the large limas White Ventura N and UC92.

    If root-knot nematodes are present in a field with a history of Fusarium wilt, choose varieties that are resistant to root-knot nematodes as well as to the particular Fusarium wilt race present when possible. Another option is to rotate with root-knot nematode resistant cowpeas (blackeyes) instead of limas.  Based on host-range tests, some varieties of cowpea have more root-knot nematode resistance than tomato. For example, some root-knot nematode races are virulent and highly pathogenic to Mi-1 gene based resistant tomatoes but not to nematode resistant cowpeas. — By Rachael Freeman Long & Amber Vinchensi-Vahl, UC Cooperative Extension

  • Selecting the ‘Right’ Walnut Rootstock

    Walnut rootstock options were historically seedlings, either Northern California Black (Juglans nigra), or Paradox (a cross between English Walnut, Juglans regia, and Northern California Black). Those two options still exist, but as research and technology advances in walnut cloning, clonal rootstocks are becoming more available. With this new advancement, growers have questions. Hopefully, I can  provide some answers.

    What is the difference?

    There is a large difference between clonal rootstocks and Paradox seedlings. This is due in part to the genetic variability, or genetic differences, in Paradox seeds. UC/UCCE/USDA Walnut researchers, specialists, and farm advisors studied the genetic background of Paradox seedlings and found high variability from one seed to the next. This means that each seed is different from the next one. One seed might be more vigorous, one seed might be  more susceptible to phytophthora , one seed might encourage more seed production, while another encourages more leaf and branch growth. This leads to a highly variable stand of trees in an orchard. Clonal rootstocks, on the other hand, are cuttings of the same plant. Walnut varieties are a good example of this process, as every Chandler tree in California came from one single mother tree which was originally produced by a seed. Much like how every Chandler tree tends to produce the same nut (some differences do develop depending on the growing conditions), every RX1 clonal rootstock will develop similar characteristics in the tree. Therefore, a Chandler orchard on a clonal rootstock tends to be more uniform in growth than an orchard on Paradox seedlings.

    What is the RIGHT choice?

    I honestly cannot think of a single “right choice” in agriculture, there’s just options. Options are nice, but they can also be confusing. Here is some background information that might help the decision in the future. RX1 and VX211 are both UC selections,  chosen from acres of single seedling crosses based on their potential benefits. These were developed as a part of the Paradox diversity study done by UC/UCCE/USDA researchers, specialists and farm advisors. RX1 appears to show some tolerance to Phytophtora, a root infecting fungus like organism, but if disease pressure is high, the rootstock may still succumb to Phytophthora. VX211 was selected based on its potential tolerance to some nematode populations, but again, much like RX1 and Phytophthora, if nematode pressure is high, VX211 may still succumb. Both RX1 and VX211 were field tested against a handful of other selections as well as Paradox and Vlach. Vlach was developed by a private party which originated from a Paradox seedling tree in our very own county of Stanislaus. The tree was selected based on its high level of vigor.

    Are any commercially available walnut rootstocks resistant to crown gall?

    Short answer: no. Long answer: Paradox seedlings, RX1, VX211, and Vlach can all be infected with the causal agent of crown gall (Agrobacterium tumefaciens) and develop galls. YET the production of clonal  material AVOIDS many opportunities for infection. Paradox seedlings are collected from the field as walnut seeds. Previous UC/UCCE/USDA research (funded in large part by nurseries) demonstrated that Agrobacterium  tumefaciens is picked up from the ground in seed orchards. Nurseries funded this research to find ways to make their production better and have since developed ways to reduce crown gall in new Paradox  seedling  rootstocks  by  incorporating the use of tarps or catch frames. That said, Paradox seedlings are highly susceptible to Agrobacterium tumefaciens and clonal material skips this field collection step. Please be advised that orchards on RX1, VX211, and Vlach still require proper sanitation, ie,  cleaning pruners/loppers with 10% bleach solution or 70% ethanol and avoid wounding  the crown, trunk, and roots during planting and other practices.

    Are these our only options?

    When excluding Blackline (please see my summer 2019 issue for further information http://cestanislaus.ucanr.edu/newsletters/ Walnut_News_-_Fruit_For_Thought80737.pdf), for now, yes, but not forever. The California Walnut Board in combination with the US Specialty Crop Research Initiative is currently funding ongoing research in the breeding and development of future rootstocks. We are looking at three to four selections for various reasons, one of  which being resistance to crown gall. These rootstocks are being field tested now and will  be made available in the future provided they prove themselves worthy, in other words capable of producing a good crop.— By Kari Arnold Ph.D. UCCE Area Orchard and Vineyard Systems Advisor, Stanislaus County

  • Potassium Nutrition in SJV Vineyards

    With summer season upon us, an understanding of the seasonal uptake of potassium (K) is essential to time fertilizer applications. Potassium is required by grapevines in large amounts and is essential for vine and fruit growth. In the spring from budbreak to bloom there is a high demand for K as new growth develops at a high rate. The most critical need for K comes later in the year during berry development and ripening. It is during this time that berries become the strongest sink for available K especially between veraison and harvest. This may be due to the berry’s high demand for K during rapid cell expansion.

    Potassium plays a key role in cell expansion and has a major role in many plant metabolic processes. Movement of K into and out of guard cells regulates the opening and closing of stomata. As such inadequate K affects stomatal regulation and can lead to excess water loss from leaves. Potassium is a key factor in the plants ability to transport and translocate assimilates which helps to promote root growth and fruit size. Potassium also plays a role in the osmotic potential regulation, which is one of the important mechanisms in the control of plant water relations and turgor maintenance. Since K can affect both the roots ability to uptake water and the leaves ability to stop water loss, deficiencies can contribute to water stress and leaf desiccation. This may be apparent as a “scorch” of the tissue. The affected leaves acquire a scorched appearance, with leaf necrosis and reddening (on red varieties) developing from the leaf margins towards the center of the leaf.

    As an essential nutrient it is recommended to use a trifold approach to assessing potassium status in the vineyard. Looking at K concentrations with soil analysis, plant tissue analysis, and visual assessment of foliage for symptoms of deficiency. Soil analysis is done pre-plant, and then every 2 to 3 years thereafter. Plant tissue analysis should be done at least every other year to monitor vine nutrition, or as needed to diagnose potential nutrient deficiency symptoms. Visual assessment is ongoing. Soil testing, however, has limitations in accurately predicting the need for additional potassium fertilizer since there are so many factors that affect uptake and utilization including soil type, texture and depth, amount of soil compaction, root pest damage, varietal, rootstock, irrigation practice and crop size. In fact, the actual K available for plant uptake represents a very small fraction of the total K in soils. This is why soil K levels have generally not ben reliable criteria for indicating the actual K status of grapevines. Petiole analysis has been the main tool for assessing K status and the need for K applications to vines. Petioles are usually collected at bloom from leaves opposite clusters on the shoot. Vines are generally sufficient at 1.5% to 2.0%, and deficiency may occur at 1.0% or less. While petiole analysis is not completely reliable tool for making K management decisions, it is the most consistent guideline currently available.

    Deficiency symptoms can appear in early spring in cool wet years, but mild deficiencies may be seen just before harvest. Visual symptoms tend to show when the grapevines are heavily cropped and maintenance applications of K have not been made in the vineyard. Deficiency is often observed in areas with sandy soils with low native K fertility, or where topsoil was removed for leveling. Compacted soils, poorly drained soils, water stress and vines with weak root systems due to presence of soil pests may also contribute to K deficiency due to poor uptake. By mid- summer symptoms of K deficiency will exhibit chlorosis of the leaf margin and between the main veins and marginal burning and curling of the leaves will develop as symptoms progress (Image 1). When deficiency is severe shoot growth is significantly reduced and vines may defoliate prematurely, especially if the crop is large.

    Fertilization programs should focus on replacing potassium loses to harvest, as well as to correct for any deficiencies found through monitoring. Wine and table grape harvests remove approximately 5 pounds of K per ton of fresh fruit. For raisins grapes this will translate into approximately 17 pounds of K removed from the vineyard per ton of dried raisins.

    In general foliar fertilization has been an economic and practical method to provide mineral nutrients, particularly micronutrients, however foliar nutrient programs of macronutrients have not been effective and economical on grapevines due to phytotoxicity tolerances, leaf barriers and limited mobility of certain elements. On the other hand, fertigation with drip irrigation both micro and macronutrients has been an effective way to manage grapevine nutrition.

    A variety of potassium products can be used in dry or liquid forms. In general, different forms of K fertilizer do not offer an advantage from each other, except to consider the use of potassium chloride, which can cause salt injury or potassium–magnesium sulfate in which magnesium can interfere with potassium uptake.

    Potassium fertilization should be applied during early spring (a few weeks after budbreak) up to veraison and is most effective when applied under drip irrigation. In the San Joaquin Valley, many soils have high K fixing capacity and can tie up to 50% or more of added K fertilizer. This K is not lost, but rather stored between layers of clay and slowly released in soil solution as exchangeable K. However, most will not be available fast enough during times of high demand, especially following veraison. Therefore, it is more practical to apply little amounts of K on weekly basis than a large amount all at once. An effective strategy for K maintenance in the San Joaquin Valley is weekly applications over the course of 10 to 15 weeks at a rate of 10 to 15 kg/ha up to veraison. Potassium fertigation is discontinued at veraison as the maturing fruit becomes a strong sink for K.

    The method of application and formulation of K will be determined by how fast the response is needed, how long it has been since any K was applied, and whether the aim is to fix a deficiency or for maintenance. Generally, there is no hard or fast rule on K application, amount, or timing. Keep in mind that the interaction of available nutrients, soil type, crop load, irrigation management, rootstock, varietal make difficult to establish a general rule that fulfills a wide range of potassium needs in the vineyard. – By Carmen Gispert, UCCE Riverside & San Diego Counties 

  • UCCE Advisor Glenn McGourty Retires, Leaves Legacy

    When Glenn McGourty arrived in Lake County in the 1970s, he was immediately smitten. “I was blown away at how special it is,” he recalled recently. “It’s just a beautiful place—unusual geology and native plants in this striking mountainous landscape.”

    More than three decades later, Glenn’s love for Lake County is as strong as ever. The region is part of him, and he is an important part of it – both its past and its future.

    Glenn is retiring as the Winegrowing and Plant Science Farm Advisor for Lake and Mendocino Counties for the University of California Cooperative Extension. He has held the position since September 1987.

    “I’ve really enjoyed working with people in Lake County,” Glenn says. “You know exactly what they’re thinking. They’re upfront and honest. They are farmers at heart.”

    A Long, Distinguished Career in Agricultural Science

    Glenn has been involved in science and agriculture his entire life. His family owned a walnut farm in Paso Robles. And when Glenn left for college, he focused on plant science, earning a bachelor’s degree in botany at Humboldt State and a master’s degree in plant, soil, and water science at the University of Nevada Reno.

    Out of college, he worked as an urban horticulturist in Las Vegas, applying the principles of science to help city dwellers with urban landscapes and gardens. It’s a theme that continued throughout his life. Today, he describes his career as being a “go-between,” linking farmers with science to help them become better agriculturalists and stewards of their land.

    Glenn credits the University of California for its vision in this area. Since its founding in 1868, UC has generated valuable agricultural research and used that knowledge to revolutionize the state of California as an agricultural leader in the world.

    Nevertheless, over a century ago, a gap remained between the research and those most in need of its benefits: farmers.

    “Someone came up with a brilliant scheme, which is that we needed a connection,” Glenn says. “We should have UC people that are really familiar with research-based scientific information, and they should work directly with farmers and the community. They should move into the community, become part of it, and work with the farmers to help them become better agriculturalists. And that’s how Cooperative Extension was formed.”

    Glenn is part of a third generation of farm advisors who started their careers in UC Cooperative Extension in the 1970s and 1980s. Now, he is readying to make way for a fourth.

    “I’ve been at it for 32 years,” Glenn said, “My job has been to bring information to the local community from other places where research has been done and to advise the growers with appropriate research-based information.”

    Focus on Sustainability and Organic Farming

    “What makes a UC farm advisor so special,” Glenn explains, “is that our work is based on scientific knowledge, not conjecture or opinions. We are also very focused on local conditions and farming challenges.”

    That approach has earned him a welcome place in the Lake County farming community. His combination of knowledge, geniality, and empathy with farmers – he is a grower himself – has made him an asset whose contributions are appreciated and will be missed.

    Glenn’s accomplishments are wide-ranging, including groundbreaking research on the effects of smoke on grapes, work on an erosion prevention education committee, spearheading an annual seminar on the latest integrated pest management research, speaking on topics such as irrigation, powdery mildew, vine hardening, and countless other efforts that have aided winegrape growers and helped protect the land.

    He is known for his support of organic and sustainable farming, particularly in winegrowing. In fact, he applies those principles to his own 10-acre winegrape and walnut farm on the Russian River. There he farms with the sustainable practices he has taught growers in Lake County and Mendocino for many years.

    He also is a champion of Lake County wines, especially Sauvignon Blanc and Cabernet Sauvignon, for which Lake County is developing worldwide acclaim. He also loves Mediterranean cultivars such as Sangiovese, Grenache, and Tempranillo, which grow very well in the high-elevation vineyards of Lake County.

    Parting Advice

    Through his career, the core of Glenn’s mission – bringing the principles of science to the practice of agriculture – has never wavered. Nor has his commitment to the farmers, especially the winegrape growers in Lake County, as evidenced by his parting advice for them.

    “Believe in yourselves,” Glenn says. “It’s awesome what Lake County has created. It hasn’t always been easy. The work takes time, and you have to prove you can be successful and consistent, year after year, particularly in the wine world. But the growers in Lake County are doing that.”

    The Lake County Winegrape Commission thanks Glenn for the many years of service and dedication he has provided to the growers of Lake County. We wish him the very best in his retirement and the adventures that await. — By the Lake County Winegrape Commission