California Fruit and Vegetable

Category: Pest/Disease Management

  • Oak Tree Mulch Study to Help Suppress Citrus Disease

    University of Florida Institute of Food & Agricultural Sciences – Florida citrus growers who face the most severe citrus disease in history notice how citrus trees under oak tree hammocks appear to tolerate the disease. Lukas Hallman believes oak trees may hold a compound that boosts the citrus trees’ ability to tolerate the disease.

    Hallman is a graduate student at the University of Florida Institute of Food and Agricultural Sciences Indian River Research and Education Center (UF/IFAS IRREC) in Fort Pierce, in the heart of the world’s premier grapefruit production region. The disease, Huanglongbing, or HLB, is caused by a bacterium and vectored by the invasive insect, the Asian citrus psyllid. Once infected, trees have a reduced fine root mass, yellowing of leaves, and smaller and bitter tasting fruit. In the U.S., the disease’s common name is citrus greening, said Hallman.

    “Anecdotal reports from Florida growers claim that citrus trees growing within the drip line of large oak trees have minimal HLB symptoms, while trees nearby, but not under the oak drip line, show severe symptoms,” said Hallman.

    Oak Extract was Medicinal During American Civil War 

    In his literature review of scientific journal articles, Hallman found that compounds from white oak tree bark were used as antimicrobials during the American Civil War. Marco Pitino, a former UF postdoctoral researcher, published the first research study for oak tree extract used in the greenhouse against the bacterium. The work took place at IRREC. Pitino found oak extract would improve citrus trees’ ability to tolerate HLB in the greenhouse.

    “The literature review and Pitino’s greenhouse study were enough to form a viable hypothesis for a field study with oak mulch beds under citrus trees,” Hallman said. “Pitino’s work took place in a greenhouse. His findings need field tests, and we need an answer to help the local industry, which has seen their crops drop by 90% in the last 15 years,” said Hallman.

    Lorenzo Rossi, assistant professor of plant root biology at IRREC, is Hallman’s graduate research advisor. Rossi persuaded Hallman to apply for a Southern Sustainable Agriculture Research and Education (SSARE) graduate student grant to fund research of his hypothesis.

    Southern Sustainable Agriculture Research & Education Grant

    When Hallman began to write the SSARE grant, a large oak tree fell on the IRREC property in a 2019 hurricane. With funds from a UF/IFAS Horticultural Sciences Department A.H. Krezdorn Memorial Fund, and collaboration with Robert Shatters, a research molecular biologist with the U.S. Department of Agriculture, Rossi and Hallman prepared the tree for mulch. The researchers used it for a bed under citrus trees in a research grove. With the research infrastructure in place, Hallman began to take monthly data from the root rhizosphere under the oak-mulched citrus tree beds.

    Rossi said Hallman’s grant application was successful, and in the fall of 2020, he began work to fulfill the project’s objectives. The SSARE grant provides more than $12,000 for the 2-year study to determine if oak mulch will suppress citrus greening in the open field.

    “The oak mulch is easier to apply to trees than the oak extract,” said Rossi. “Through the research, we may find oak mulch soil amendments improve the soil and that the compounds in the mulch help citrus trees tolerate HLB.”

    The project, “Deploying oak mulch to contain and suppress HLB disease in citrus,” has three objectives: to determine the capability of oak mulch to contain and suppress citrus greening, to measure the effect of oak mulch on HLB-affected citrus physiology, root growth and development, and to study the effect of oak mulch on microbial life biodiversity within the rhizosphere. Hallman carries out daily data collection for the project. Those tasks include soil samples, soil respiration, photosynthesis measurement, and nutrition studies.

    Graduate student Lukas Hallman distributes oak mulch on citrus tree beds.

    “With the SSARE project, we are able to expand the research,” said Rossi. “In the future, we will need to identify which compounds are beneficial, where those compounds are in the trees, which oak species hold the specific compounds, and how much of the right compounds will control the disease.”

    One year into the project, Hallman said he found more nutrients in the root rhizosphere. Also, preliminary findings show that as the mulch breaks down, soil biodiversity increases.

    “More nutrients are available to the trees as a result of the mulch breaking down into the soil,” said Hallman. “The nutrients are potassium and phosphorus. We have also found that mulch improves soil texture. Improved soil holds more moisture and requires less irrigation.” Soil that holds more moisture enhances plant root health and the trees’ nutrient uptake, resulting in more fruit and a longer life for the trees, Rossi said.

    “The research is a collaboration with the USDA,” said Rossi. “It confirms that UF/IFAS and the USDA are committed to the development of ‘an out-of-the-box’ cure for HLB.”

    Longterm outcomes for the research are to improve economic profitability for growers, to improve environmental health by reducing chemical inputs, and to support the surrounding community. In the years from 2006 until 2011, HLB took more than 6,500 jobs from Floridians. Oak mulch could help restore some of those positions, said Hallman.

  • Stay Vigilant with Asian Citrus Psyllid Finds on the Rise

    In the past few months, we have seen sporadic Asian citrus psyllid (ACP) detections popping up across California. While the citrus industry’s efforts have thus far kept Huanglongbing (HLB) out of commercial groves, these recent ACP detections are a reminder that we cannot let our guard down. The most effective way to prevent the spread of HLB is to keep psyllids out of our orchards.

    After ACP detections in multiple counties (Kern, Madera, San Luis Obispo, Santa Barbara, Santa Clara, Tulare, Contra Costa and others) were confirmed earlier this fall — including areas with historically low ACP activity — the Citrus Pest & Disease Prevention Committee is encouraging all growers to stay informed, scout for ACP and treat when advised.

    The recommendations outlined in the Voluntary Grower Response Plan, developed collaboratively by growers and scientists, represent the most effective tools known to the citrus industry at this time and are meant to supplement the California Department of Food and Agriculture’s required regulatory response. You can help prevent the spread of ACP by following these best practices, participating in recommended winter treatments and ensuring haulers and transporters are tarping loads.

    While we should expect to see this type of “flare up” occasionally, we need to remain vigilant – even when things are quiet – to ensure we continue to stay on top of this elusive pest and the dangerous disease it spreads. The upfront cost to manage ACP is much less than the potential hit to our industry if HLB spreads throughout the state. To date, HLB has only been identified in backyard citrus trees in Los Angeles, Orange, Riverside and San Bernardino counties, and hasn’t made its way into a commercial citrus grove yet. To keep HLB out of commercial citrus, psyllid control is especially critical this season with warmer weather encouraging more pests.

    Here is what you can do:

    • Follow the best practices outlined in the Voluntary Grower Response Plan for Huanglongbing
    • Participate in treatment strategies recommended by the University of California (UC)
    • Adhere to tarping regulations that help keep pests from hitching a ride to new areas of the state

    Visit citrusinsider.org for more information and resources on the voluntary grower best practices, tarping regulations and UC treatment recommendations.

    Questions?
    Contact your regional grower liaison for the latest information on detections near you and coordinated or area-wide treatment schedules. Find your grower liaison here.

    Let’s work together to protect California citrus for your businesses, neighbors and generations to come.

    Sincerely,
    Jim Gorden
    Chair, Citrus Pest & Disease Prevention Committee

  • Root Bacteria Could Help Defeat Fatal Citrus Disease

    A UC Riverside-led team is looking at tiny underground microorganisms for a way to prevent a huge problem — Huanglongbing, a disease with no cure that has decimated citrus orchards worldwide.

    The disease, also known as HLB or citrus greening, has multiple names but the same ultimate result: bitter and worthless citrus fruits. By some estimates, the end of citrus orchards in California and Florida could amount to $14 billion in lost commercial revenue.

    Fruit affected by Huanglongbing. (UCR)

    “Often times, it is thought of as an above-ground disease of the fruits, leaves, and stems,” said Caroline Roper, plant pathology professor and director of the new research effort. “However, we have seen the roots of trees decline with infection, and we want to understand why.”

    The National Institute of Food and Agriculture has awarded the UCR-led team $10 million over the next five years to investigate the role of soil and root microbes in the disease.

    Roper said data from previous studies shows the microbiome of the infected tree — which includes bacteria and fungi as well as protozoa and viruses — plays a role in the disease.

    “We have seen a shift in the root microbiome as trees get sicker,” she said.

    The microbiomes shift to contain more potentially parasitic organisms that may act as secondary invaders to a tree that is suffering from HLB, according to Roper. The invasion of these root pathogens may be causing trees to die faster when they have HLB.

    Part of this new research effort will test whether soil amendments like manure and compost might suppress parasitic microorganisms in the roots as well as the soil, and give the trees more strength to combat diseases including HLB.

    In addition, the research team will try to determine the molecular basis of HLB resistance shown by citrus root stocks developed in Florida. They’ll then see how those rootstocks perform in California, which has different soil and climate conditions.

    The research team will examine both younger trees, because a lot of citrus growers have had to re-plant their orchards after infection, as well as older trees to see if mature groves can recover.

    It will also be important to note how well root stocks from Florida, where there has been a heavy infestation of HLB, perform in California, where much less of the disease has been detected.

    “One of the great things about this grant is that we’re able to leverage existing field trials being done by our collaborators in Florida and at the UC’s Lindcove Research and Extension Center in central California,” Roper said. “This may lead to faster results than we’d otherwise have had.”

    Collaborators on the project include UC Davis; California State University, Sacramento; the University of Florida; and the U.S. Department of Agriculture’s Agricultural Research Service in Ft. Pierce, Florida. — By Jules Bernstein, UC Riverside

  • 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

  • $12 Million to Eradicate an Invasive Rodent of Unusual Size

    You may have heard of them in the comedy film Princess Bride as “Rodents of Unusual Size”, but this is the real thing — only not so large and formidable.  Nutria were originally introduced into the United States as part of the fur trade in the late 1800s, but were eradicated from California in the 1970s.  They made a sudden reappearance a few years ago, and are a great threat to our water infrastructure, indigenous wildlife, and even certain crops. Watch this brief interview with Brian Popper from USDA-APHIS Wildlife Services, who spoke about a number of wildlife pests at Malcolm Media’s annual Tree & Vine Expo recently.
     
    Please thank this video’s sponsor Suterra for their industry support.

  • $12 Million to Eradicate an Invasive Rodent of Unusual Size

    You may have heard of them in the comedy film Princess Bride as “Rodents of Unusual Size”, but this is the real thing — only not so large and formidable.  Nutria were originally introduced into the United States as part of the fur trade in the late 1800s, but were eradicated from California in the 1970s.  They made a sudden reappearance a few years ago, and are a great threat to our water infrastructure, indigenous wildlife, and even certain crops. Watch this brief interview with Brian Popper from USDA-APHIS Wildlife Services, who spoke about a number of wildlife pests at Malcolm Media’s annual Tree & Vine Expo recently.
     
    Please thank this video’s sponsor Suterra for their industry support.

  • University of Florida Awarded Grants to Continue Fight Against Citrus Greening

    University of Florida researchers hope to discover new methods to help citrus growers fight the deadly citrus greening (or Huanglongbing) disease with cost effective, long-term sustainable treatments with the support of recently awarded federal grants.  Three teams of scientists from UF’s Institute of Food and Agricultural Sciences received nearly $4.5 million in U.S. Department of Agriculture funds to study new ways to manage the invasive insect causing millions of damage to Florida’s citrus crops.

    “These grants build on an existing portfolio of success in finding solutions to combat citrus greening throughout Florida’s citrus groves,” said Michael Rogers, director of UF/IFAS Citrus Research and Education Center and coordinator of the UF/IFAS statewide citrus program. “They will contribute to the solutions we are providing that support citrus growers in sustainably and profitably growing citrus throughout the state.”

    Managing the Asian citrus psyllid with the environment in mind

    Bryony Bonning, eminent scholar and professor in entomology and nematology, leads a team from Gainesville and the UF/IFAS Citrus Research and Education Center in Lake Alfred, Florida in a project that uses a bacteria-derived pesticidal protein combined with gene silencing to manage the invasive Asian citrus psyllid (ACP) population. The long-term goal of the proposed work is to create an environmentally benign approach for citrus growers to control ACP that works within an integrated pest management (IPM) strategy. The project intends to identify the optimal components for an ACP control product for grower use.

    The grant project aims to: 1) optimize ACP-active proteins derived from the bacterium Bacillus thuringiensis (Bt) that suppress psyllid populations, 2) further develop genetic solutions that would disrupt ACP, and 3) screen for the best combination of these methods for use against ACP. On completion of this project, researchers will be well positioned to produce transgenic citrus and/or trap plants that will suppress ACP populations for use by citrus growers.

    This method of effective vector control, combined with other measures will help the citrus industry in Florida rebound, and protect the industries in California and Texas. The results of this research are anticipated to reduce the need for tree removal and replanting as well as reduce insecticide applications, and increase yields and fruit quality, contributing to the long-term profitability and sustainability of U.S. citrus production.

    Attacking citrus greening from the inside out

    Amit Levy, assistant professor of plant pathology, received a NIFA grant to examine how the Candidatus Liberibacter asiaticus (CLas) bacteria interacts with a narrow tissue – known as the phloem – which is buried inside the stem of the citrus tree. CLas resides in and plugs the phloem in the stem of the citrus tree, leading to inhibition of sugar and nutrient transport into the tree’s sink tissues, including the fruit. Eliminating these plugs can presumably result in renewed sugar transport and increased fruit yields.

    However, there is a significant gap in understanding CLas-phloem interactions in citrus, which has been a major limiting factor for controlling the disease. Levy and a team of UF/IFAS researchers and Sainsbury lab and Cornell University scientists plan to address these challenges with a novel seed coat-based system that supports in-depth analyses of phloem dynamics and CLas-phloem interactions in HLB-affected citrus. The project will identify key players required for phloem plugging, host immune response and CLas colonization inside the phloem. These key players can later become novel targets for manipulation with gene editing techniques that can be translated into usable products, such as transgene-free CRISPR/Cas9 edited plants to block the disease propagation and movement, and increase sugar and nutrient translocation into fruit thus increasing tolerance or resistance to HLB.

    A Novel Therapeutic Strategy For HLB-Infected Trees

    Huanglongbing (HLB)-resistant or tolerant citrus trees are the long-term solution for citrus greening disease.  Existing research has generated transgenic citrus lines that provide robust tolerance to HLB. These transgenic lines are already in field tests as a potential management possibility for HLB. However, these trees will have to go through an extensive approval process before being made available to growers.

    A research team lead by UF/IFAS microbiology and cell science professor Zhonglin Mou and faculty from the UF/IFAS Citrus Research and Education Center and UF/IFAS Southwest Research and Education Center are working to speed up this process by reproducing the greening resistant or tolerant genetic makeup in non-transgenetically modified plants by gene editing using CRISPR/Cas9. This is a better long-term approach but will take time.

    The primary goal of this project is to develop an interim treatment for HLB. The project hopes to turn off the genes that negatively control the citrus immune system and result in disease symptoms in citrus when exposed to disease-causing pathogens. Coupled with other work to target the HLB-causing bacterium itself, the overall goal is to develop new management strategies making citrus varieties highly tolerant to this disease. The project will use a vector derived from citrus tristeza virus (CTV) to remove negative regulation of the citrus immune system, leading to improved immune response and HLB tolerance. The same CTV vector will also deliver antimicrobial peptides to reduce HLB pathogens.

    The synergism between the immune system-provided tolerance and the antimicrobial peptide-mediated pathogen reduction is expected to provide effective control of the HLB disease. Importantly, CTV naturally occurs in the field and does not make genetic changes to the citrus genome, and thus the employed strategy is a non-transgenic approach. — By Ruth Borger, University of Florida

    The mission of the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is to develop knowledge relevant to agricultural, human and natural resources and to make that knowledge available to sustain and enhance the quality of human life. With more than a dozen research facilities, 67 county Extension offices, and award-winning students and faculty in the UF College of Agricultural and Life Sciences, UF/IFAS brings science-based solutions to the state’s agricultural and natural resources industries, and all Florida residents.

  • UC Cooperative Extension Investigates the Reality of Steam-Weeding Lettuce Fields

    Despite the tremendous need, there are currently no preemergence herbicides that are organic-compliant. Steam injected into the soil such that the soil temperatures reach >140°F for 15-20 minutes will kill weed seed in the soil. The effect of this reduction in the seedbank viability results weed control in the treated area that persists for several weeks or months, similar to the effects of a preemergence herbicide.

    Two studies were conducted at the USDA Hartnell Farm at Salinas, CA during July to September 2020. Steam was applied to raised beds using a custom-built steam injector. Prior to seeding lettuce, steam was applied in a 4-inch wide band to a depth of 3 inches deep. The steam was supplied by a SF-20 Sioux steam generator at approximately 6 to 9 PSI. Soil temperatures in the treated zone were monitored overnight with Hobo temperature monitors. Treatments tested were steam, steam plus 1% w/w peroxide, and nontreated. Treatments were replicated 4 times and arranged in a randomized complete block design. Peroxide was included as it releases heat when injected into soil, i.e., an exothermic reaction, based on the premise that it supplements the heat released by steam. Data collected were soil temperatures following steaming, weed control, hand weeding times, diseased plant counts, and lettuce yields. Trial 1 was initiated July 1 and harvested August 31, 2020. Trial 2 was initiated July 21 and harvested September 25, 2020. Soil temperature intervals >140°F in the top 4 inches of soil for steam were 88 and 67 minutes for trials 1 and 2, respectively. Similarly, soil temperatures >140°F in the steam + peroxide treatment were 76 and 80 minutes for trials 1 and 2, respectively. In trial 1 steam and steam + peroxide resulted in 90% and 92% weed control relative to the nontreated. In trial 2 steam and steam + peroxide resulted in 66% and 84% weed control, respectively. Steam alone reduced hand weeding times 22% to 35% compared to the nontreated, and steam + peroxide reduced hand weeding times 36% to 40% compared to the nontreated. There were no differences in numbers of plants with lettuce drop (Sclerotinia minor) in trial 1. Compared to the nontreated, lettuce drop incidence in trial 2 was 66% and 59% lower in steam and steam + peroxide treatments, respectively. Lettuce plant diameters in trial 1 found that lettuce grown on steamed soil was 16% larger, but there were no differences in trial 2. Lettuce plants grown on steam + peroxide treated soil were 12% and 23% larger in trials 1 and 2, respectively. There were no treatment effects on yields in either trial 1 or 2.

    We are not aware of any commercial scale applicators for lettuce that apply steam in a band to the lettuce bed. However, we are working with Dr. Mark Siemens, an agricultural engineer with the University of Arizona to design a commercial scale applicator. Mark has a prototype applicator built and will be demonstrating it during the winter season in the Yuma Valley. It appears that the design for a steam applicator is not complicated and is well within the capabilities of machine shops in California to build. — By Nelly Guerra & Steven Fennimore, UC Cooperative Extension

  • CDFA Accepting Proposals for Riverside County Grower Liaison

    The California Department of Food and Agriculture (CDFA) is currently accepting proposals for its Request for Proposal for a contractor to serve as the Riverside County grower liaison. Proposals must be received by Nov. 18. Responsibilities may include conducting outreach directly to growers in Riverside County, providing them up-to-date information on the latest industry news or updates, staying engaged in CDFA activities, communicating voluntary or mandatory treatments Riverside County and more.

    The battle to save California citrus from the Asian citrus psyllid (ACP) and Huanglongbing (HLB) is a collaborative effort that involves local, county, state and federal officials, researchers, scientists and commercial citrus growers. To help facilitate pest management and disease eradication, grower liaisons are key pieces to that puzzle and are dedicated to serving a specific region in the fight against HLB.

    This position requires a fundamental knowledge of citrus production, a working knowledge of grove operations, and the relationship between growers, shippers and allied businesses that work in the area of pest and disease control. A Pest Control Advisor’s license is desirable, but not required. The contractor should be familiar with California agriculture and specifically its citrus industry. Knowledge of the ACP and HLB is desirable.

    To submit a bid for the contract, you must follow these steps:

    • Visit ca.gov, if you do not have a profile you must register for one in order to view the Request for Proposal (RFP).
    • Once logged in, visit the Get Public Procurement Information page and select “See current bids.”
    • Under “Search Events,” type in “Asian Citrus Psyllid Outreach and Education.”
    • Once on the Events Details page, click “View Event Package,” then under the “View Attachments” area, click “view” to download the official Request for Proposal. Once there, you should be able to view the full RFP and Start a Bid if you meet the qualifications. Please note, you must have a profile and be logged in to view the RFP.

    Proposals are due to CDFA by Nov. 18 at 2 p.m. The term of this contract is Dec. 1, 2020 or upon final signature, whichever is later, through Nov. 30, 2022.

    For additional questions, contact Contracts Analyst Donna Weber at donna.weber@cdfa.ca.gov.

  • USDA Study Reveals Airborne Fungus Can Trigger Plant Growth

    The U.S. Department of Agriculture’s (USDA) Agricultural Research Service (ARS) recently announced that a harmless airborne fungus, Cladosporium sphaerospermum strain TC09 (TC09), can dramatically accelerate plant growth if a germinating plant is near the fungus as it emits volatiles or gases.

    Scientists used tobacco and pepper plants as models to study the conditions for accelerated plant growth once exposed to TC09. Following a relatively short duration of exposure at the seedling stage, the plants began to sense the fungi’s volatiles and gases. USDA scientists were then able to stimulate extremely rapid plant growth, earlier flowering and fruit yield increases.

    “This is a game-changer for agriculture and for research that seeks innovative ways to accelerate plant growth,” said USDA Scientist Dr. Chris Dardick. “Its implications are far-reaching and will help ARS’ commitment to deliver cutting-edge scientific advances for American farmers and producers.”

    The effects of TC09 were largely correlated with the duration of exposure. Visual observation indicated that plants with TC09 exposure for 10 days exhibited substantially more vigorous growth, thicker stems, larger leaves, and a more robust root system relative to plants without fungal exposure. Results also showed that treated plants flowered 20 days sooner and pepper plants yielded up to 213 percent more fruit that was ready for harvest three weeks earlier than untreated controls. More recent studies have shown similar research results for numerous other crops such as lettuce, arugula, kale, basil, and other leafy greens.

    This species of fungus is commonly found in indoor environments and is not known to cause disease in plants or any ailments in humans or animals. Also, unlike other microbial species that have been tested, the researchers showed that TC09 does not induce defense or stress responses in exposed plants. Scientists hope to identify the specific volatiles and gases that stimulate plant growth in future research.

    Research on microbial biostimulants that enhance plant growth has recently intensified because they provide an eco-friendly, cost-effective and sustainable strategy to benefit agriculture. USDA scientists will continue to study TC09 and seek practical strategies to apply it during commercial crop production, particularly for urban and indoor agricultural systems. They are awaiting approval of a patent and commercial evaluation license and partnered with NASA to apply this research technology to spaceflight conditions. This research was supported in part by grants from USDA-ARS, ARS’ Appalachian Fruit Research Lab, and the Oak Ridge Institute for Science and Education.

    The Agricultural Research Service is the U.S. Department of Agriculture’s chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in agricultural research results in $20 of economic impact.