California Ag Network

Category: Food Safety

  • Protein Discovery Could Help Enable Eco-Friendly Fungicides

    New research reveals an essential step in scientists’ quest to create targeted, more eco-friendly fungicides that protect food crops.

    Scientists have known for decades that biological cells manufacture tiny, round structures called extracellular vesicles. However, their pivotal roles in communication between invading microorganisms and their hosts were recognized only recently.

    UC Riverside geneticist Hailing Jin and her team found plants use these vesicles to launch RNA molecules at fungal invaders, suppressing the genes that make the fungi dangerous.  

    ​Infection of an Arabidopsis plant by the fungus that causes white mold disease. (Anna Schroll/Max Planck Institute for Chemical Ecology)

    “These vesicles shuttle small RNAs between cells, like tiny Trojan horses with weapons hidden inside,” said Jin, a professor of genetics and the Cy Mouradick Chair in the Department of Plant Pathology and Microbiology. “They can silence pathogenic fungal gene expression.”

    Using extracellular vesicles and small RNAs has several advantages over conventional fungicides. They’re more eco-friendly because they are similar to naturally occurring products. Eventually, they degrade and do not leave toxic residues in the soil. Also, Jin explained, this method of fighting fungi is less likely to breed drug-resistant pathogens.

    A sticking point for scientists in creating these fungicides has been figuring out how to load their desired small RNAs into the vesicles.

    “We’ve wondered how these weaponized small RNAs get into the bubbles,” Jin said. “Now, we think we have an answer.”

    Her laboratory has identified several proteins that serve as binding agents, helping to select and load small RNAs into the vesicles. The lab’s research is detailed in a new Nature Plants journal article.

    The Jin laboratory has been working for several years on the development of gene-silencing RNA fungicides. Work toward this goal led to the team’s landmark discovery in 2013 that gene-silencing RNA messages can be sent from the fungal pathogen to the plant host to suppress host immunity. Later, the team learned small RNAs can move both ways — from plants into pathogenic invader cells as well. In 2018, the team worked out that extracellular vesicles were the major delivery system for these small RNAs. They observed that Arabidopsis plants secrete extracellular vesicles into Botrytis cinerea, a fungus that causes grey mold disease and destroys millions of crops every year.

    “This was the first example of a host using these vesicles to deliver small RNAs to another organism,” Jin said. “Previously we saw movement of RNA, but didn’t know how the small RNA are selected and transported.”

    Now, she and her colleagues have identified several RNA-binding proteins in Arabidopsis that bind to specific small RNA molecules and load them into extracellular vesicles. This suggests the proteins play an important role in loading and stabilizing small RNAs in the vesicles. The finding can help increase the payload of gene-silencing RNAs that make it into vesicles and enhance the efficiency of disease control.

    Some scientists have taken inspiration from the RNA communication in plant vesicles to design human therapies. For example, some are attempting to load anti-cancer RNAs and drugs into extracellular vesicles in fruits or vegetables, so people can eat or drink them. Jin is hopeful that her lab’s discovery can aid these efforts. — By Jules Bernstein, UC Riverside

  • UC Davis Wants Samples of Your Fermented Foods for Science

    It’s not always easy to find silver linings during the COVID-19 pandemic, but here’s one that food scientists at the University of California, Davis, have discovered: More people are exploring the ancient art of fermented foods.

    “My mom made her first batch of sauerkraut this summer,” said Maria Marco, a microbiologist and food science professor with the UC Davis College of Agricultural and Environmental Sciences. “With so many of us sheltering-in-place, fermented foods are more popular than ever.”

    Marco takes more than a culinary interest in America’s latest food trend. Marco and Erin DiCaprio, a food safety expert and Cooperative Extension specialist at UC Davis, are investigating the microbial mysteries of fermented fruits and vegetables to better understand the role fermentation can play in healthy diets.

    And you can help.

    “We’re calling on people from across the state to send us samples of their home ferments so we can characterize their microbial composition,” Marco said. “Citizen scientists can help us expand the body of knowledge about the nutritional content and beneficial bacteria in fermented fruits and vegetables.”

    Marco, DiCaprio and their team of mostly undergraduate student scientists are looking for “fresh” ferments that are composed mainly of fruits and vegetables. By fresh, they mean samples taken right after fermentation, before refrigeration. They will be collecting samples for the next year. If you live in the Davis or Sacramento area, they can arrange to pick up your sample. If you live outside the area, or want to learn more, contact the team at EAT LAC (as in, lactic acid).

    Managing microbes

    Fermented foods and beverages are produced by nurturing conditions that discourage the growth of harmful bacteria and encourage the growth of beneficial microorganisms. Take sauerkraut, for example. When you combine cabbage, salt, time and the right temperatures, you can help friendly microbes flourish. As they do, they convert sugars in the cabbage into lactic acid and other compounds with tangy flavor that keep harmful bacteria at bay.

    Similar chemistry is at work when producing a long list of fermented foods, such as yogurt, cheese, bread, alcohol, chocolate, coffee, salami, vinegar, kimchi, miso, tempeh and pozol.

    Besides adding new flavors and textures, fermentation can extend the shelf life of food, improve our ability to absorb some nutrients and — perhaps — provide an environment for beneficial bacteria to thrive in our digestive systems and help prevent chronic disease.

    “It’s quite possible that consuming fermented foods as part of a regular diet supports a healthy digestive tract and the microorganisms living in our intestine,” Marco said. “Our health may be helped by what those microbes eat, as well as by the nutrients they produce. Our goal is to provide solid evidence that can show whether fermented foods can, indeed, help fight disease. And if so, how.”

    Tips for fermenting safely at home 

    What’s the best way to ferment fruits and vegetables at home? DiCaprio is working with the UC Master Food Preserver Program to provide online fermentation classes.

    In the meantime, here are DiCaprio’s top tips:

    • Follow a research-based recipe, like the ones you can find at UC Food Safety, the USDA Complete Guide to Canning and the National Center for Home Food Preservation. “Some of the resources available online and in print haven’t been vetted for safety,” DiCaprio said. “They might not have you add enough salt in the beginning, for example, which is important for keeping your product from spoiling.”
    • Sanitation matters: Keep hands, equipment and the preparation area clean and sterile throughout the fermentation process.
    • Control temperature: Don’t let your ingredients get too hot or too cold.
    • Monitor the process to make sure it’s fermenting properly — that little bubbles are slowly rising to the surface, for example, and that mold isn’t growing throughout the container. “You can’t just set something on a counter and forget about it,” DiCaprio noted.
    • Skim the scum. It’s common for a layer of yeast and mold to form atop your vegetable brine after a few days. DiCaprio recommends skimming it off each day.

    “And be sure to start with good, fresh ingredients,” DiCaprio said. “We look forward to seeing the samples!” — By Diane Nelson, UC Davis, Food & Agriculture

    Purple cabbage used to make sauerkraut changes to a light pink color as it starts to ferment. (Hector Amezcua/UC Davis)

  • Insect-Deterring Sorghum Compounds May be Eco-Friendly Pesticide

    Compounds produced by sorghum plants to defend against insect feeding could be isolated, synthesized and used as a targeted, nontoxic insect deterrent, according to researchers who studied plant-insect interactions that included field, greenhouse and laboratory components.

    For this study, at the University’s Russell E. Larson Agricultural Research Center, researchers grew two nearly identical lines of sorghum — alike except that one, a mutant, did not possess the functional gene responsible for producing the flavonoids that essentially poison corn leaf aphids. Then researchers compared how the lines were faring.

    The researchers examined the role of sorghum chemicals called flavonoids —specifically 3-deoxyflavonoid and 3-deoxyanthocyanidins — in providing resistance against the corn leaf aphid, a tiny blue-green insect that sucks sap from plants. To defend against pests like the aphids, sorghum has evolved defenses that includes biosynthesis of secondary metabolites, including flavonoids to poison the pests.

    A previous Penn State study showed that in sorghum, accumulation of these flavonoids is regulated by a gene called yellow seed1 that controls responses to stresses such as fungal pathogens, noted Surinder Chopra, professor of maize genetics, Penn State. His research group in the College of Agricultural Sciences led both studies.

    In the current research carried out at the University’s Russell E. Larson Agricultural Research Center, researchers grew two nearly identical lines of sorghum — one with a functional y1 gene that produced flavonoids, and the other a mutant called null y1, which did not possess the functional yellow seed1 gene responsible for producing the flavonoids.

    The flavonoids are not present in the phloem — vascular tissue in plants that conducts the sugars aphids seek — but are in the epidermal cells that form the outermost layer of defense. When aphids repeatedly probe and puncture the epidermal cells with their stylets, or beaks, they take up the flavonoids that lead to their demise.

    When they compared the two lines of plants, researchers found that a significantly higher number of adult corn-leaf aphids colonized null y1 plants compared to the plants with functional y1 gene that produced flavonoids. The aphids actively fed on the null y1 plants to where some of them showed signs of stress with yellowed leaves. The functional sorghum plants that produced the flavonoids had much lower aphid numbers and showed no ill effects from aphid feeding.

    Greenhouse experiments with similar potted sorghum plants demonstrated that the aphids clearly preferred to feed and reproduce on null y1 plants, and the adults produced many more nymphs.

    In a companion laboratory experiment, researchers fed two groups of adult aphids diets of sorghum leaf tissues — but to one they added an extract containing the flavonoids. After a few days, most of the aphids that fed on the flavonoid-enriched leaf tissue died and reproduction was curtailed — none of those aphids had nymphs before they succumbed.

    On sorghum that didn’t have the functional gene to produce the flavonoids, researchers found that a significantly higher number of adult corn leaf aphids colonized on them and fed actively to the point that some of the plants showed signs of stress with yellowed leaves.

    Perhaps surprisingly, Chopra explained, the flavonoids are not present in the phloem — vascular tissue in plants that conducts the sugars aphids seek — but are in the epidermal cells that form the outermost layer of defense. When aphids repeatedly probe and puncture the epidermal cells with their stylets, or beaks, they take up the flavonoids that lead to their demise.

    The findings, published online in the Journal of Chemical Ecology, indicate flavonoids can potentially be deployed as potent insect deterrents to protect crops, Chopra suggested.

    “Sorghum plants have evolved to precisely emit compounds offering defenses against harmful predatory insects that threaten them, and yet these chemicals in their defenses don’t hurt beneficial insects,” said Chopra. “If we could develop nontoxic insecticides, it would be a game changer — given that the toxicity of synthetic pesticides is of great concern, and they are considered to be dangerous to human health.”

    Chopra, supported by Penn State, has applied for a patent on using flavonoids as insect deterrents. He pointed out that while much more research needs to be done, the most important consideration is that flavonoids are natural plant products that do not cause any pollution and are not harmful to human or animal health.

    several varieties of Sorghum

    This research may be an early step toward developing new phytochemicals for crop defenses, Chopra believes. “How well the flavonoids work against other herbivores is being researched, but we know with corn leaf aphids they are very, very potent,” he said.

    Also involved in the research at Penn State were postdoctoral fellows Iffa Gaffoor and Sampurna Sattar, and Cullen Dixon, an undergraduate student, all in the Department of Plant Science; Nadia Frock and Juliet Moen, students in the Department of Entomology; and Associate Dean of Research Gary Thompson, professor of plant science. The team included Consuelo De Moraes and Mark Mescher, Department of Environmental System Science, ETH Zurich; and Rupesh Kariyat, Department of Biology, University of Texas Rio Grande Valley.

    The research was supported by the U.S. Department of Agriculture’s National Institute of Food and Agriculture. — By Jeff Muhollem, Penn State University

  • Improved Method to Test for Mycotoxin in Feed

    California Department of Food and Agriculture (CDFA) Center for Analytical Chemistry (CAC) scientists Bahar Nakhjavan, Nighat Sami Ahmed, and Maryam Khosravifard were recently published in an academic journal after developing an improved method to test for mycotoxin in feed. Their article, “Development of an Improved Method of Sample Extraction and Quantitation of Multi-Mycotoxin in Feed by LC-MS/MS,” details their research of evaluating the three most popular sample preparation techniques for determination of mycotoxins, then selecting the best method and optimizing it.

    Mycotoxins are the most common contaminants in agricultural crops produced by several species of mold and fungi. During growth, maturity, harvest, storage and processing of food and animal feed products, the fungus produces mycotoxins and other secondary metabolites. Mycotoxin-contaminated food and feed threaten human and animal health even at very low concentration.

    Nakhjavan, Ahmed and Khosravifard work in CDFA’s CAC Environmental Safety Laboratory. Testing for mycotoxin in food and animal feed in the Regulatory Analysis Laboratory is part of their job of preventing contaminated food and feed from being consumed by humans, livestock and poultry in California. CAC uses state-of-the-art equipment and processes to test fruits, vegetables, nuts, animal feed, milk, water and air to ensure that pesticide and chemical levels are within the safety range established by national and international standards. Additional CAC staff who contributed to the work discussed in this published paper include Sally Henandez, Jose Salazar and Sarva Balachandra.

    Click here to read “Development of an Improved Method of Sample Extraction and Quantitation of Multi-Mycotoxin in Feed by LC-MS/MS,” by CAC scientists Nakhjavan, Ahmed and Khosravifard.

    (L-R) CDFA scientists Bahar Nakhjavan, Nighat Sami Ahmed and Maryam Khosravifard.

  • Organic Ag Takes on Climate Change

    The threat that climate change poses to our world, our ecosystem and our health demands bold policy solutions, and, as the devastating impacts of a warming Earth mount, the push for the development of robust and comprehensive federal climate policy is gaining traction. Organic agriculture can be a part of the solution and help tackle climate change through its ability to reduce greenhouse gas emissions, store away huge amounts of carbon, and enable farmers to be resilient in an evolving climate.

    The Organic Trade Association on Thursday released a major report on organic and its ability to mitigate climate change, identifying policy opportunities to elevate the role of organic in the climate change discussion, support organic farmers and encourage transition to organic farming. Reflecting close dialogue with organic stakeholders and the association’s membership, the white paper, “Advancing Organic to Mitigate Climate Change,”  incorporates the key principles identified by the Organic Trade Association Board of Directors to achieve meaningful climate policy solutions.

    The trade association also recently announced the launch of a Climate Task Force, open to all Organic Trade Association members. The task force will amplify the Organic Trade Association’s voice in climate policy discussions by advocating for policies that address the association’s core principles and sharing recommendations with lawmakers and key stakeholders.

    “Our climate crisis is real, is immediate, and affects us all. It is clear that urgent action is needed to help us mitigate and adapt to this crisis,” said Avi Garbow, Organic Trade Association Board member and Environmental Advocate for Patagonia Works. “While the nation’s conventional agricultural sector’s emissions and practices contribute to our worsening climate, there is a time-tested climate solution that regenerates our soils, nourishes our communities, and safeguards our environment from harmful synthetic chemicals: organic agriculture.”

    Garbow, a nationally recognized environmental leader who served as the General Counsel at the Environmental Protection Agency from 2013-2017, added, ”The Organic Trade Association, through the work of its members, the Climate Task Force and its research and analysis, will ensure that organic is well-positioned to play a leading and cost-effective role in stemming and ultimately reversing the effects of our changing climate.”

    Organic Priorities in the Climate Change Fight
    Organic agriculture provides a critical opportunity to mitigate climate change and at the same time create economic, environmental and health benefits for all those involved in our food system–from the grower and the processor, to the distributor and the consumer. But although public and private initiatives to support organic as a climate mitigation tool exist, stronger federal support is needed for organic to reach its full potential to fight against climate change.

    The Organic Trade Association’s Board of Directors early this year determined that organic had to be elevated in the climate change policy discussions that are increasingly taking place in the halls of Congress, in government offices, in corporate boardrooms. The Board also agreed that the Organic Trade Association, as the leading voice in the nation for the organic sector, should spearhead the effort to advance organic as a solution to climate change and to protect organic from the risk of climate change. A climate task force consisting of seven Board members was formed with the goal of developing principles for good climate policy to guide organic’s engagement in climate policy discussions.

    In June at the association’s annual meeting, the Board unanimously endorsed ten principles for climate policy. 

    The Organic Trade Association will engage in smart climate policy solutions that:

    1. Advance organic agriculture. Any policy that addresses the role of climate change in food and agriculture should advance the opportunity for organic to be a climate change solution, allow organic to be successful, and not undermine organic.

    2. Are science-based, data-driven and verifiable. Policy solutions should be based on and supported by science and data, with strong verification measures to meaningfully reduce agriculture’s impact on climate change.

    3. Focus on outcomes and continuous improvement. Policies should reward the outcomes of good agricultural practices and enable a system of continuous improvement that achieves specific positive outcomes over time.

    4. Promote soil health and carbon sequestration.  Improving soil health is an important and central component in addressing agriculture’s role in climate change. Policies should include provisions for advancing soil health and carbon sequestration. .

    5. Lower the use of fossil-fuel based chemicals. Chemical fertilizers and pesticides are a key source of greenhouse gas emissions in agriculture. Climate policies should minimize the use of and eliminate the dependency on fossil-fuel based inputs, especially synthetic nitrogen fertilizers.

    6. Provide solutions for mitigation and adaptation. Policies should provide the resources to not only mitigate the impacts of climate change but also help the agricultural sector adapt to a changing climate. 

    7. Incentivize farmers and businesses. Farmers should not have to bear the brunt when making transformational changes. Public and private sector programs should provide tools and resources to achieve outcomes through market-based incentives or financial payments that encourage conservation practices or ecosystem services.

    8. Decarbonize the economy. Policies that increase greenhouse gas emissions or rollback progress in decarbonizing the economy and reducing emissions should be opposed.

    9. Foster agricultural diversity and innovation. Climate policies should foster diversity and innovation in farming systems, and provide incentives for increasing diversity in cropping systems.

    10. Address equity and inclusion. Policies should address the environmental and economic inequities caused by climate change, and include ways to support disadvantaged communities in adapting to climate change.

    “Among the many threats posed by the climate crisis, perhaps the greatest is the potential it has to impact food production.  The good news is that organic farmers are already focused on building soil health and eliminating the use of synthetic fertilizers, two steps that can help agriculture shift from being a source of greenhouse gas emissions to being a net sink,” said Britt Lundgren, Director of Organic and Sustainable Agriculture at Stonyfield Farm and member of the association’s Board. “At Stonyfield we are excited to be working with the Organic Trade Association’s Climate Change Task Force on advancing organic agriculture as a climate change solution. The climate change principles adopted by the association provide a roadmap for how federal policy can support climate mitigation and adaptation in agriculture.”

    Recommendations to Support Organic’s Battle on Climate Change
    Incorporating the Organic Trade Association’s guiding principles to fight climate change, the new white paper offers specific recommendations for policymakers to support organic farmers and encourage transition to organic farming as a key strategy for climate change mitigation.

    “As a company that has made organic food for over 30 years, Amy’s has witnessed firsthand the inherent benefits of organic agriculture on the health of the planet. The Organic Trade Association’s Climate Change White Paper, through scientific research, provides a practical set of policy recommendations to make organic agriculture a bigger and more meaningful part of the climate change solution. We look forward to seeing the positive impact of this important work,” said Paul Schiefer, Senior Director of Sustainability at Amy’s Kitchen and member of the association’s Board of Directors.

    Specific policy recommendations in the white paper include:

    •Elevating organic as a key voice in climate-smart agricultural policy;

    •Establishing a national program to support transitioning organic farmers by reducing financial risks, improving market infrastructure development and increasing access to land;

    •Developing a competitive grant program to provide technical services to organic and transitioning farmers to create better access to information about organic production methods that sequester greenhouse gases and improve crop yields;

    •Creating a federal Healthy Soils pilot program, based on existing programs at USDA’s Natural Resources Conservation Service and the California Healthy Soils Initiative.

    “Extreme weather variability, caused by climate change, is the greatest challenge facing farmers,” said Doug Crabtree, Montana organic farmer and member of the Organic Trade Association Board of Directors. “The (over)use of synthetic nitrogen fertilizers is agriculture’s most egregious contribution to climate change. Organic farmers demonstrate that farming systems can be productive, profitable and a significant part of the solution to climate change by avoiding synthetic nitrogen, building soil organic matter and sequestering carbon in the soil. I am proud that our trade association is taking the lead on illustrating the key role of organic food and farming in managing climate change.”

    “U.S. communities, economies and ecosystems are under threat from climate change,” said Laura Batcha, CEO and Executive Director of the Organic Trade Association. “Federal policies can help advance organic as a key solution by encouraging the adoption of organic practices and maximizing benefits for mitigating climate change. The Organic Trade Association and our members stand ready to engage and support federal lawmakers in advancing these recommendations.”

    To download the white paper and for more information on the association’s new Climate Task Force see OTA.com/climate.

    The Organic Trade Association (OTA) is the membership-based business association for organic agriculture and products in North America. OTA is the leading voice for the organic trade in the United States, representing over 9,500 organic businesses across 50 states. Its members include growers, shippers, processors, certifiers, farmers’ associations, distributors, importers, exporters, consultants, retailers and others. OTA’s Board of Directors is democratically elected by its members. OTA’s mission is to promote and protect ORGANIC with a unifying voice that serves and engages its diverse members from farm to marketplace.

  • Irrigation Strategies to Avoid Heat Damage to Cool Season Vegetables

    Currently, we are experiencing a prolonged heatwave on the central coast.  Heatwaves have become a recurring phenomenon in recent years, especially in late summer. With thousands of acres of cool season vegetables in the ground, irrigation will be critical for keeping crops cool and for supplying enough moisture to meet their water needs.

    Crops can be kept cool by maximizing evapotranspiration (ET).  As liquid water vaporizes heat is lost from the surfaces of leaves and soil and from the surrounding air, which cools the temperature of the crop.  Under water stress leaf stomates close during the hottest period of the day (11 am to 4 pm) and the temperature of the plant tissue can rise above the temperature of the surrounding air.  If the temperature becomes too great leaves and other plant parts may become scorched.

    Since most ranches have a limited number of wells and personnel to irrigate, it is challenging to assure that each field has adequate soil moisture to prevent plants from overheating.   A good strategy is to irrigate just enough to refill the soil profile to the rooting depth of the crop.

    To prioritize which fields to irrigate one should consider the water holding capacity and existing level of moisture of the soil, as well as rooting depth and developmental stage of the crop.  For example, a lettuce crop near maturity with a high ET demand, growing on a sandy textured soil that feels dry, should probably be irrigated soon.  A young lettuce crop with a low ET demand, growing on silt loam soil that still feels moist, likely can be irrigated later without suffering heat damage.

    Another consideration for prioritizing which fields to irrigate are recent field operations.  A recently transplanted vegetable field may need to be irrigated first but may not need a long irrigation to re-saturate the soil around the roots.  A crop that was recently cultivated may have pruned roots, and therefore may need water soon to prevent wilting under these hot conditions.

    Table 1 estimates how much moisture is available to a vegetable crop between saturation and moderately dry or dry conditions for different soil textures.  This table can be a guide for how much water should be applied to re-saturate the soil.  For example, applying 0.42 inches per foot of rooting depth will bring a moderately dry silty clay soil back to saturation.  Applying more than this amount of water will likely over-saturate the root zone.

    Table 1. Estimated plant-available moisture for different textured soils.

    Also, estimating the cumulative crop ET since the last irrigation can guide how long to irrigate. Reference ET values between south Salinas and Soledad during this hot spell have been as high as 0.27 inches per day.  If the crop has a full canopy, 0.25 to 0.3 inches for each day since the last irrigation would be a good rule of thumb for how much water to apply as long as the total does not exceed the water holding capacity of the soil.

    Lastly, one needs to convert the amount of water to apply to an irrigation run-time.  To make this calculation one needs to know the application rate of the irrigation system. For impact sprinklers, the application rate can be estimated using Tables 2-4.  Note that pressure and nozzle size have a significant effect on application rate.  For drip, the irrigation time will depend on the tape discharge rate and pressure, as well as the spacing of drip lines.  Assuming that the drip system is operated at the pressure recommended by the manufacturer (usually 8 to 10 psi) one can use Table 5 to approximate the application rate.  For example, for one drip line of medium flow tape (0.45 gpm/100 ft) on 40- inch wide beds the application rate of the drip system is 0.13 inches per hour. If there are several drip lines per bed then multiply the application rate in the table by the number of drip lines.

    The appropriate run-time can be estimated by dividing the amount of water to apply by the application rate of the irrigation system.  For example, to apply 0.6 inches of water to a field with drip using medium flow tape the water would need to run for 4.6 hours:

    Hours to operate the irrigation system = 0.6 inches of water/0.13 inches per hour = 4.6 hours

    Summary

    Irrigating the right amount of time to bring the soil back to saturation will maximize crop ET during these hot days, and hopefully prevent any heat damage to crops.  Also, consider visiting the CropManage website (cropmanage.ucanr.edu) for further guidance on scheduling irrigations. This online tool can assist growers in quickly estimating how much water to apply to meet crop water needs.

    Table 2.  Sprinkler application rate for varying pressures and nozzle diameters for a solid set spacing of 30 × 30 feet (Rainbird 20JH).
    Table 3.  Sprinkler application rate for varying pressures and nozzle diameters for a solid set spacing of 30 × 33.3 feet (Rainbird 20JH).
    Table 4.  Sprinkler application rate for varying pressures and nozzle diameters for a solid set spacing of 30 × 40 feet (Rainbird 20JH).
    Table 5.  Drip application rates for varying bed widths and tape flow rates estimated for 1 drip line per bed.  Multiply the rate in the table by the number of drip lines per bed to determine the actual application rate.  (For 3 drip lines on an 80-inch bed multiply by 3)
    “— By Michael Cahn, UCCE Farm Advisor, Monterey County”

  • New Targets for Huanglongbing Treatments

    Scientists are closer to gaining the upper hand on a disease that has wiped out citrus orchards across the globe. New models of the bacterium linked to the disease reveal control methods that were previously unavailable.

    Metabolic models of organisms are like road maps of cities. “They show you all the biological processes, and how they work together,” said UC Riverside microbiology professor James Borneman. “They also show you which molecular pathways, if blocked, will kill the organism.” 

    Simplified metabolic model and its striking similarity to a road map. (Metallo&Vander Heiden)

    In this case, researchers created the first models of the bacterium associated with Huanglongbing or HLB, also known as citrus greening disease. The team’s work is described in a new paper published in Nature’s npj Systems Biology and Applications.

    The research team made models for six different strains of the bacterium known as CLas and doing so enabled them to identify as many as 94 enzymes essential for the bacterium’s survival. These enzymes can now be considered targets for the creation of new antibacterial treatments.

    In addition, the team identified metabolites required for the bacteria to grow.

    “Just like when humans break down the food they eat into small components called metabolites, which feed our cells, bacterial cells also require metabolites for their growth,” Borneman said.

    Knowing the metabolites needed for CLas’ growth could enable scientists to cultivate it in a laboratory setting. It is not currently possible to grow CLas on its own, hindering scientists’ ability to study it and ultimately to manage it.

    This research project involved a collaboration between UC Riverside, UC San Diego, Texas A&M University, and the U.S. Department of Agriculture. In addition to Borneman, members of the modeling team included UCR plant pathologist Georgios Vidalakis and UCSD systems biologist Karsten Zengler.

    UC Riverside is at the forefront of efforts to combat Huanglongbing. Other important areas of research include antibacterial development and delivery, immune system fortification in citrus, engineering resistant citrus via a detailed understanding of host-microbe interactions, breeding resistant citrus, and insect management, among others.

    Because microbes tend to mutate and acquire resistance mechanisms in response to drugs and other efforts to thwart them, Borneman cautions that any one solution to the problem may be short-lived.

    Transmission electron microscope image of CLas bacterium. (J.M. Bové/INRA)

    “Microbes almost always adapt to control measures, perpetuating the ‘arms race’ between pathogens and hosts,” Borneman said. “There won’t be one thing that will fix this disease. We likely will need to address all three components associated with the disease — the bacterium, the insect that transmits it, and the citrus plants — to find a long-lasting solution.”

    To that end, the research team is constructing metabolic models of citrus and the insect, the Asian citrus psyllid.

    “We expect that this multiorganism modeling endeavor will provide new insights into the mechanisms underlying this disease, which will lead to effective and sustainable Huanglongbing management strategies,” Borneman said. — By Jules Bernstein, UC Riverside

  • Barking Up the Right Tree: Canines Detect HLB

    In September 2019, huanglongbing—also known as HLB or citrus greening—was detected in residential citrus trees located in Ventura County, in southern California (and just recently, the first HLB carrying Asian Citrus Psyllid was detected in a commercial CA citrus grove).

    During an orchard review in California, expert detector dog, Szaboles alerts his trainer by sitting next to a citrus tree infected with Huanglongbing (HLB).

    The disease, which has no known cure, is caused by a bacterium that devastates citrus plants and is transmitted by psyllids (small plant-eating insects resembling lice) that carry the bacteria from tree to tree or by the grafting of infected plant material. Common symptoms of infection include blotchy mottling of entire leaves, premature defoliation of the tree, and fruits that are usually small, with green peel at the bottom and a bitter taste. Unfortunately, these visible signs of HLB do not manifest until months or even years after the initial infection. By then, it is too late for citrus growers to save their crop from a mass infestation.

    However, the Farm Bureau of Ventura County found a rather unconventional way around this problem.

    To contain the infected trees and prevent a citrus epidemic, the Farm Bureau decided to hire a team of detector dogs specially trained to find HLB bacteria. The dogs are a result of a unique program funded by USDA and run by Agricultural Research Service (ARS) Research Leader and Plant Pathologist Timothy Gottwald (now retired) at the U.S. Horticultural Research Laboratoryin Fort Pierce, FL.

    First, the clever canines patrolled the perimeter because the edges of a grove are where the disease would first accumulate. Then, they trotted through the grove of trees to ultimately identify over 200 infected trees from a grove of 3,500.

    According to Gottwald’s research, the canine-detection method has an accuracy rate of 99 percent. While humans need several minutes to visually examine each tree and collect samples for laboratory testing (which requires considerable lab time and supplies), the dogs can travel through groves of trees in mere minutes, sensing HLB-infected trees by smell faster and far more easily. The time saved in finding the disease earlier gives citrus growers the opportunity to remove and destroy or quarantine HLB-infected trees, controlling what could’ve been a severe outbreak and loss of crop.
     

    However, there are still some considerations to keep in mind when deploying the canines as an early detection technology. Each dog team can only work 30 minutes at a time before they must rest, and a new team takes over. Teams can work for about 6 hours a day. In addition, much like any lab equipment, dogs are periodically calibrated to the HLB “scent signature” to remain finely honed optimized detectors.

    Still, the dogs are more sensitive and accurate than any other available technology in the field. The employment of detector dogs is still a voluntary program, which means fruit growers and farmers have the choice to either use dogs to find HLB early or continue using a USDA-approved DNA test called polymerase chain reaction (PCR).

    “While PCR is an effective way to detect infections, it isn’t efficient,” Gottwald explained. “It’s difficult to pinpoint incomplete infections—or infections that are only on one part of a plant (for example, a single leaf out of an entire tree with possibly thousands of leaves)—using PCR because it requires numerous samples from all over the suspect specimen.”

    “On the other hand,” Gottwald continued, “detector dogs identify pathogens ‘holistically,’ easily locating minute infections regardless of what small part of the tree they are infecting.” With this increased scope and accuracy rate, Gottwald and his colleagues believe that the canines’ abilities will revolutionize how growers protect their crops.

    “These specially trained canines may also be used to detect diseases and infections in other fruits and vegetables, such as grapes, peaches, plums, and tomatoes,” he said. “Our research has shown that they can sense pathogens like plum pox virus or squash vein yellowing virus, which both can cause severe economic losses to agriculture industries.”

    The canine-detection method was validated in blind tests by USDA ARS in collaboration with the California Department of Food and Agriculture, with results published in 2020.— By Georgia Jiang, USDA-ARS

  • Dairy Methane Reduction Programs: Providing Great Bang for the Buck

    California dairy methane reduction programs are providing a valuable mitigation strategy in the state’s efforts to fight climate change. A growing body of evidence shows that the Dairy Digester Research and Development Program (DDRDP) and Alternative Manure Management Program (AMMP)have proven to be among the state’s most cost-effective approaches for reducing greenhouse gas emissions.

    The California Department of Food and Agriculture (CDFA) recently released its 2020 report of dairy digester projectsfunded through the DDRDP. Anaerobic digesters, like the one pictured here, capture biogas from decomposing manure, which can be used to create renewable fuel or electricity. The 108 dairy digesters funded to date are already reducing 6 percent of the total greenhouse gas (GHG) emissions from all California agriculture. That’s a reduction of 19.9 million metric tons of carbon dioxide equivalents (MMTCO2e) over ten years. Alternative manure management projects avoid the creation of methane emissions by promoting drier handling and storage practices. The AMMP has funded a total of 105 of these projects, which are estimated to reduce about 1.1 MMTCO2e over 5 years.

    These programs stand out as top performers in California’s climate investment portfolio. The 2020 annual climate investment report shows that the DDRDP provides more GHG reductions than any other program (more than double the reduction of the next-ranking program). At a cost of $9 per ton of GHG reduction, the DDRDP is also the second most cost-effective of the 68 programs. This is in due in no small part to the matching private funds being invested at a 2 to 1 rate, helping the state leverage its investment and greatly expand the benefits. At a cost of $49 per ton of GHG reduction, the AMMP is the seventh most cost-effective of the 68 climate programs funded by the state.

    There’s another reason why California’s climate-smart dairy programs stand out: they reduce methane. Unlike carbon dioxide (CO2) and other long-lived GHG’s, methane is short-lived in the atmosphere, which means a reduction can have a cooling effect within a shorter amount of time. Leading climate scientists are now recognizing that reducing methane emissions can quickly stabilize the climate pollutant’s powerful impact and actually help offset the damaging impact of CO2—the state’s most significant GHG—which accumulates and persists in the atmosphere for hundreds of years.

    In a recent preliminary analysis of progress, the California Air Resources Control Board (CARB) documented that significant ongoing state incentive funding will be needed to achieve the state’s dairy and livestock methane emission reduction target created by Senate Bill 1383 (Lara, 2016). The analysis verifies that the DDRDP and AMMP have been highly effective. CARB also estimates that an additional $85 million in incentive funding will be needed each year between now and 2030 to make the additional reductions needed. This shows that CARB understands incentive funding remains very important, as the state seeks to reduce methane from smaller dairies. Early incentive funding led to the development of digesters on some of the larger dairies in the state, as these projects were able to demonstrate greater economies of scale. While the total costs of digester projects is less for smaller dairies, the cost per cow is higher. As a result, to be economically viable and successful, adequate incentive funding will be even more essential moving forward.

    California’s significant progress on dairy methane emissions reduction has not happened by accident. It has occurred because California had the foresight to structure a voluntary incentive-based approach to prevent the emission leakage that would occur from command and control regulation. The voluntary incentive-based approach—carried out through the DDRDP and AMMP—has worked well, helping take dairy farms more than halfway toward the state’s dairy methane reduction goal. Additional investments will help to not only meet the state’s methane-reduction goals, but also its overarching, ambitious climate targets.

    California’s dairy methane reduction programs are the state’s most effective climate mitigation tools.

  • NEW NITROGEN MANAGEMENT RESOURCE AVAILABLE FOR CITRUS & AVOCADO

    To address nitrate pollution of groundwater, the Central Valley Regional Water Quality Control Board has initiated a regulatory program requiring growers to utilize nitrogen management practices that mitigate nitrate loading. Because nitrogen plays such a critical role in in the growth and development of avocado trees — and because it can be difficult to ensure trees are receiving the optimal amount of nitrogen — the University of California Department of Agriculture and Natural Resources has created the Nitrogen Management in Citrus and Avocado publication.

    This document is designed to optimize growers’ application of nitrogen while reducing nitrogen leaching by focusing on applying nitrogen at the right rate, at the right time with the right placement and from the right source (otherwise known as the four R’s of nutrient management). The guide provides specific examples for the rate of application based on the age, alternate bearing status and vegetative state of the tree and discusses the optimal spring/fall application periods. In addition, the document provides guidance on how to conduct leaf analysis and what optimal concentration percentages to look for.