Pacific Nut Producer Magazine

Tag: UC Davis

  • Assessing the Costs & Benefits of Winter Cover Cropping in CA

    Winter cover cropping is a promising agricultural management practice that boosts soil health. This article discusses a benefit-cost analysis of winter cover crop adoption and introduces a web-based interactive calculator for farmers to assess changes to baseline farm profits.

    Winter cover cropping is an agricultural management practice that can enhance soil health while protecting fields from soil erosion and compaction. Cover crops are typically grown on farmland that would otherwise be left fallow in the wintertime, such as fields used for annual spring-summer crops, or in between rows of trees or vines, and thus do not replace a cash crop. Despite its well-known soil health and ecological benefits, and popularity in other parts of the U.S., winter cover crop adoption rates are low across California’s specialty crops. To better understand drivers and incentives for adoption, we created a benefit-cost calculator that estimates how baseline profits change as a farmer integrates winter cover cropping.

    This tool was designed for specialty-crop farmers who are interested in growing winter cover crops and want to understand how long it will take for that investment to break even. However, the tool is useful for anyone interested in better understanding the financial implications of cover cropping. In this article, we explain the methodology behind the tool and how to use it.

    Methodology

    We developed a calculator that estimates the expected changes in expenses and revenues associated with the introduction of winter cover cropping for a given farming operation. We started by modeling the implications of winter cover crops to average farms that grow processing tomatoes and almonds, two of California’s most important agricultural commodities. The model estimates a benefit-cost ratio in present value terms, i.e., the ratio of the sum of benefits over the sum of costs accumulated over time and discounted to the present.

    In our baseline analysis, we considered cover crop seed mixes that are commonly used for winter cover cropping in California’s Central Valley. For tomato operations, this was assumed to be a small grain forage mix (e.g., bell beans, winter peas, common vetch) and for almonds, this was assumed to be a more expensive clover mix.

    Table 1 lists potential benefits and costs of winter cover cropping. Benefits and costs are not the same every year. The monetary values for each of these components are incorporated into the model at the specific time when that benefit or cost is likely to be experienced.

    Benefits include increased income from greater yields, which results from improvements in soil quality, fertility, and soil-water relations due to cover cropping. Benefits also include reductions in expenses associated with soil erosion control, nutrient cycling, weed control, mycorrhizal fungi colonization, and reduced tillage operations. Almond growers may also benefit from lower beehive prices.

    The potential for cover crops to affect the irrigation requirements of cash crops is debated in the scientific literature. Cover crops may lead to higher water infiltration (resulting from improved porosity of the top soil), which can lead to increased capture of winter and spring rainfall, increased soil-water storage, which in turn can delay irrigation start and eventually reduce spring/summer irrigation requirements slightly; however, these effects are soil-specific and difficult to quantify and generalize and, thus, are not included in the baseline model. Other potentially valuable aspects of cover cropping that were not explicitly accounted for in the analysis include reduced soil sealing and compaction, better soil oxygen concentration and diffusion rates, as well as increased effectiveness of salt-leaching practices.

    Furthermore, while cover cropping has been shown to improve ecosystem services and downstream user benefits, these are not included in the baseline benefit-cost calculations. These societal benefits, which include increased soil organic matter, the protection of downstream surface water quality via reduced runoff, and carbon sequestration through enhanced soil-carbon storage, were not included because they would not accrue as a revenue flow to the farmer choosing to adopt.

    Costs include the initial expenses associated with cover crop seeds, planting, and termination, depreciation of machinery used for this management practice, and time spent learning how to incorporate cover crops into an operation, as well as disseminating new instructions to crewmembers. The model accounts for financial losses due to potential harvest complications with cash crops. For example, a heavy rain at the end of March could delay termination of cover crops, and thus delay the planting of tomato seedlings, which can postpone the timing of tomato harvest. This poses a potential complication for farmers who contract with tomato canneries, resulting in penalties.

    To quantify these benefits and costs, we collected data from UC Ag Issues Center’s Cost and Return Studies, scientific publications, semi-structured farmer interviews, and field experiments to establish an average value of each benefit and cost component. We then aggregated these components to estimate benefit-cost ratios for tomato and almond production systems, where a value of the ratio greater than 1 indicates a net positive change in profits. The interactive calculator is seeded with the average value for each benefit and cost component, but can be adjusted by the user to reflect a specific farming operation. While our model attempts to be as comprehensive as possible, some potential benefits or costs are not included, such as interactions with pruning or other practices.

    Results

    When using average values for all the benefit and cost components, we find that almond systems have a benefit-cost ratio greater than 1 when considering a 30-year time horizon, meaning that benefits are likely to exceed costs on average. When using average values for the tomato system, we find the benefit-cost ratio to be less than 1, given their assumed 10-year time horizon. The time horizons of 10 and 30 years were chosen for tomato and almond operations, respectively, to reflect typical rotation patterns and crop life cycles. Figure 1 displays these results year-over-year. At the 10-year mark for tomatoes and the 30-year mark for almonds, the average benefit-cost ratios are 0.5 and 1.3, respectively, indicating that total benefits eventually outweigh total costs for almond operations, but not tomatoes.

    Winter cover cropping is an investment in the long-term viability of agricultural operations. The benefits and costs accrue differently over time and may vary from year to year. Harvest complications with a cash crop reduce profitability but can be avoided with flexible contractual obligations or by growing a cover crop with predictable senescence. Overall, our results show the value of this soil management practice is greatest for California farmers with a longer time horizon and willingness to manage a cover crop as carefully as their cash crop.

    Interactive Web-based Calculator

    The web-based cover crop calculator, partially shown in Figure 2 and available here, is an interactive decision-support tool that calculates the benefits and costs of winter cover cropping in almond and processing tomato operations. The tool estimates how much farmers can expect their profits to change after growing winter cover crops for a certain number of years. All values used in the calculator are flexible and can be adjusted to match the reality on any commercial farm. The calculator is seeded with the average values for each cost and benefit component that we considered, but the user can easily adjust or remove any component.

    The calculator assumes continuous cover cropping after the year of adoption (first year), and that all benefits of cover crops begin accruing within the first five years. Importantly, the tool may not capture every potential benefit and cost from introducing cover crops into a farming operation. It simply serves as a guide to when a farm can expect to experience economic returns, based on the monetized benefits and costs.

    As mentioned previously, cover crops could either increase or decrease spring-summer irrigation requirements. Although this component is not included in the baseline net present value model, the calculator is flexible in this variable. The user can specify the extent to which cover crops increase or decrease irrigation requirements in the growing season and can add irrigation costs to germinate the crop if needed, and then observe how their baseline profits shift accordingly. Users can also explore how a financial incentive, in the form of an annual subsidy payment per acre of cover-cropped farmland, will affect their outcomes. The calculator allows one to value the social benefits of cover cropping (ecosystem services, carbon sequestration, and downstream water quality) via this subsidy component. – By Ellen Bruno, Alyssa DeVincentis, Samuel Sandoval Solis, and Daniele Zaccaria, UC Giannini Foundation of Agricultural Economics, University of California

    Authors’ Bios

    Ellen Bruno is an assistant Cooperative Extension specialist in the ARE department at UC Berkeley. Alyssa DeVincentis is a Ph.D graduate from UC Davis in Hydrologic Sciences. Samuel Sandoval Solis is an associate professor and Cooperative Extension specialist and Daniele Zaccaria is an associate Cooperative Extension specialist, both in the Department of Land, Air and Water Resources at UC Davis. They can be reached at ebruno@berkeley.edu, ajdevincentis@ucdavis.edu, samsandoval@ucdavis.edu, and dzaccaria@ucdavis.edu, respectively. 

  • Grower Survey to Address Future Innovations in Weed Management

    Weeds can be a significant problem in berries, tree fruits, tree nuts, and vine crops (e.g. grapes, hops, etc.) especially after transplanting and during flowering and fruit and nut set. Herbicides are a primary tool for managing weeds, even though the evolution of herbicide resistance has limited the utility of many products and off-target movement can sometimes result in damage to trunks, shoots, leaves and flowers. Many growers are transitioning to organic systems to address changes in consumer preferences or satisfy the requirements set in place to enter export markets.

    Perennial cropping systems are exploring technologies such as automated harvesters and pruners, to reduce labor demands, and canopy sensing sprayers, to minimize the amounts of crop protection chemicals applied to shrubs, trees, and vines. Novel weed control tools that eliminate or reduce the need for herbicides are actively being developed for and marketed in the agriculture and horticulture industries. These new technologies could begin to play and increasingly large role in future crop production, particularly in high-value specialty crops that 1) have limited herbicide options, 2) are sensitive to herbicide injury, and 3) are heavily reliant on a labor market that is simultaneously growing more scarce and more expensive.

    A team of weed scientists from UC Davis, Oregon State University, and Cornell are asking berry, tree fruit, tree nut, and vine crop growers to take 5 to 10 minutes and answer this short and anonymous survey (link below) about your current weed management practices and your interest in novel technologies, like vision-guided sprayers and cultivators, and electric, steam, and pressurized water weeders. This will help us plan research and extension projects that will address stakeholder concerns regarding the future of weed management.

    There’s always a chance that we forgot to include some amazing tools that are emerging on the horizon; please feel free to e-mail Lynn Sosnoskie at lms438@cornell.edu and let her know what you think the future of weed control will look like.

    Thanks for your time. We appreciate your support of weed science research.

    Survey link: https://cornell.ca1.qualtrics.com/jfe/form/SV_bEpfAijoP7puQDP

  • Main Fungal Canker Diseases Affecting California Almonds

    In California, fungal canker diseases have long been known to affect almond trees. However, they have become an increasing concern to growers in recent years as they are affecting a greater extent of young trees, eventually resulting in significant tree losses. Canker diseases can also become prevalent in mature orchards, impacting yield, the lifespan of trees, production costs and overall profitability of almond orchards. Ultimately, trunk and scaffold canker diseases constitute a major cause of tree death and branch dieback in California almond orchards.

    As the University of California (UC) Assistant Cooperative Extension Specialist in Plant Pathology for fruit and nut crops when I receive calls from farm advisors, almond growers and Pest Control Advisers (PCAs) the questions they most frequently have are in relation to canker diseases, asking how can it be diagnosed, and how can it be treated.

    Symptoms on affected trees are very conspicuous and often alarming to growers. Moreover, field diagnosis of canker diseases is difficult as symptom delineation among the various canker diseases is not clear. Hence, laboratory tests are usually required to obtain accurate disease diagnosis, which is essential to the implementation of appropriate management strategies.

    With support from the Almond Board of California (ABC) and with the help of farm advisors, my laboratory conducted statewide surveys to characterize canker diseases in almond orchards and to get a thorough understanding of the main diseases and pathogens present. This work has provided molecular tools and a database for the accurate identification of fungi commonly isolated from almond cankers.

    This article will provide an overview of the main canker diseases that impact almond trees and how they can be recognized. But first, let’s review some general concepts about canker diseases.

    What is a canker?

    A canker in woody plants generally refers to a lesion produced in the bark of a plant’s stem, twig, or branch, often resulting in a dead area that can block water and nutrient transport to portions of the tree, thus causing parts of the plant to die back. Most cankers are caused by fungi, which invade bark tissue and the current season’s wood. However, some fungi colonize in both bark and internal wood tissue, causing canker rot or wood cankers that persist for years.

    Wood cankers typically consist of brown-to-dark brown discoloration of xylem tissues and may vary in shape from wedge-shaped to round, or irregular. 

    What are the main infection pathways and disease cycles of canker diseases?

    In orchard systems, cankers usually originate around wounds such as pruning wounds, mechanical injuries, sunscald and sunburn lesions, as well as wounds caused by insect borers. In almonds, canker pathogens infect trees mainly through pruning wounds made for primary and secondary scaffold selection to provide the general structure of trees. Cracks in the tree crotch or on the trunk as well as shaker injuries provide other entry points for canker-causing pathogens in almonds. Canker diseases may go unnoticed during the early stages of infection, though symptoms become more visible as the trees age.

    Most fungal canker pathogens produce fruiting bodies on dead wood of infected host plants. The spores produced by these fruiting bodies serve as inoculum for new infections, mostly during wet weather. The vegetation present in the vicinity of orchards, particularly trees in riparian areas or neighboring orchards of susceptible crops, may serve as inoculum sources for fungal canker pathogens affecting almonds. Once a canker disease has been established in an orchard, infected almond trees can provide additional inoculum for further infection. 

    Does stress play a role in the exacerbation of canker disease?

    Recent outbreaks of canker diseases in perennial crops have been attributed in part to drastic changes in production practices, climate change and increased plant stress, the continuing adaptation of pathogens to new environments, and, most importantly, the global movement of plant material. Ultimately, though, trees suffering environmental stresses are more susceptible to canker diseases.

    Microorganisms that usually do not cause disease in non-stressed hosts may become opportunistic pathogens of stressed plants. Increases in canker diseases are common during extended periods of drought or following sudden temperature fluctuations. Drought stress can also impair the plant’s ability to defend against fungal invasion. Conversely, excessive watering can kill roots and predispose plants to canker pathogens.

    What are the main canker diseases in California almonds, and what are their symptoms?

    Ceratocystis canker

    Ceratocystis canker, caused by the fungal pathogen Ceratocystis destructans (formerly known as Ceratocystis fimbriata), is one of the most prevalent canker diseases in California almonds – it occurs statewide in all almond producing counties. While this disease is generally associated with shaker damage and bark injuries on trunks during harvest, C. destructans is also capable of infecting branches from fresh pruning wounds and if left untreated can kill branches, scaffolds and entire trees. Ceratocystis is spread by several species of sap-feeding beetles and fruit flies.

    Ceratocystis canker starts as water-soaked injuries that are darker than the surrounding healthy tissue. Symptoms of established infections include amber-colored gumballs that are produced around the margin of the canker, where the fungus is most active. The cankers are perennial, persist over several years, and are most active during the growing season. Young trees infected with Ceratocystis canker may die rapidly while infections in older trees usually progress slowly. 

    Band canker and other Botryosphaeriaceae cankers

    Although band canker was first reported years ago as a disease in almonds, it’s appearance had been very sporadic up until the last decade, when this disease was suddenly being reported in large numbers of commercial orchards and causing severe damage.

    Band canker

    Band canker produces unique symptoms that include oozing amber sap that forms in a ring around the circumference of the tree. Young, vigorous varieties that grow quickly from aggressive nitrogen and water inputs are especially prone to band canker. Solid sprinkler irrigation or micro-sprinklers that wet the tree trunk can create conditions favorable for infection.

    Band canker is often an annual disease that occurs when trees are in their second-to-fifth leaf and usually does not necessarily reappear the following year. However, an increasing number of cases have been reported lately where cankers are being re-activated in following year. Tree death due to band canker has become more common as multiple bands can develop as the canker continues to grow from one growing season to the next.

    Botryosphaeriaceae cankers are characterized also by gumming around pruning wounds made near the trunk or in main scaffold branches. Band canker and Botryosphaeriaceae cankers are particularly common in young almond orchards in the northern San Joaquin Valley and well as in the Sacramento Valley.

    Infections by Botryosphaeriaceae fungi are usually associated with growth cracks or pruning wounds on the trunk and main scaffold branches. Studies have revealed there are at least 12 different Botryosphaeriaceae species in almonds, each with various levels of virulence. Among them, Neofusicoccum species, including N. parvum and N. mediterraneum, are the most common in California. Neoscytalidium dimidiatum also occurs frequently in cankers developing around pruning wounds on the trunk. This pathogen also can cause shoot blight and fruit rot in almonds.

    Eutypa dieback

    Eutypa dieback in almonds occurs sporadically in the Sacramento Valley and in the northern San Joachim Valley. Eutypa dieback is caused by the fungus Eutypa lata and is a common disease in apricots, sweet cherries and grapevines. Eutypa dieback in almonds is usually found in young trees.

    Cankers mostly originate from pruning wounds on limbs or trunks as well as from cracks formed at the junction of scaffold branches and the trunk, extending downward toward the graft union or upwards into one or more scaffold branches. Amber-colored gum turning dark brown to reddish brown normally exudes around the cracks. Irregular-shaped to wedge-shaped, brown-colored cankers are observed from cross sections of limbs and trunks.

    Limb dieback may occur several months or years after infection. The fungal fruiting bodies, i.e. the perithecia of E. lata. are rare in almond orchards, suggesting sources of inoculum for this disease most likely originate from surrounding susceptible hosts including apricot and grapevine as well as natural host plants in riparian areas such as willows. 

    Cytospora cankers

    Cytospora species have been isolated sporadically in almond orchards in California, Cytospora canker is generally associated with pruning wounds in the branches of third-leaf trees or older. At least five species of Cytospora have been associated with cankers in California almonds. Symptoms of Cytospora canker include longitudinal cankers in branches and scaffolds often associated with pruning wounds, vascular discoloration of the wood and moderate gumming.

    Florent Trouillas, UC Davis Plant Pathologist

    Cytospora species have been traditionally thought to be secondary to sunburn and other stresses or injury in stone fruits. However, their prevalence in cankers together with pathogenicity studies suggest that this group of fungi constitutes virulent pathogens. Overall, Cytospora pathogens are of increasing concern in recent years in many fruit and nut crops in California.— By Florent P. Trouillas (Through the Almond Board of California), Assistant Cooperative Extension Specialist in the Department of Plant Pathology at the University of California, Davis

    Stay tuned for a follow-up article from Trouillas on how growers can manage different types of canker diseases in their orchards. Growers are also encouraged to check out the Univeristy of California IPM website for more information on various types of canker diseases.

  • COVID-19 Impacts on Food Supply Chain (May 12 Zoom Call)

    Why is milk being dumped and produce left to rot in fields while grocery store shelves go empty during the COVID-19 pandemic? Why are grocery stores running out of meat, and eggs becoming so expensive?

    The head of California’s Department of Food and Agriculture, researchers from the University of California, Davis, and food purveyors will tackle these and other questions in an online panel discussion at 5 p.m. Tuesday, May 12.

    UC Davis invites the public to attend “Food Shortages in a Pandemic” over the web through Zoom conferencing. To do so, register online at least 48 hours in advance.

    The 90-minute event, which will include a question-and-answer period with the Zoom audience, will feature:

    • Karen Ross, secretary of the California Department of Food and Agriculture since 2011
    • Dan Sumner, director of the UC Agricultural Issues Center, professor of agricultural and resource economics at UC Davis, and former assistant secretary for economics at the U.S. Department of Agriculture
    • Bu Nygrens, co-owner and director of purchasing at Veritable Vegetable of San Francisco, which distributes organic produce from more than 200 small and mid-size growers to restaurants, markets and co-ops across five states
    • Chelsea Minor, corporate director of public affairs for Raley’s Supermarkets of West Sacramento, a regional grocery chain in Northern California and Nevada

    Moderating the event will be Catherine Brinkley, who, as an assistant professor in the Department of Human Ecology at UC Davis, studies the architecture of food supply networks. 

    The panel will discuss how the food supply chain works, why the COVID-19 pandemic has been so disruptive, how distributors and supply chains are adapting to serve restaurants and grocery stores, and whether changes can or should be made to make food systems more resilient.

    The lecture is the third in the Savor series, which explores some of the biggest food and beverage topics being studied today at UC Davis — a world leader in the study of agriculture. The series is presented by the Robert Mondavi Institute for Wine and Food Science and the UC Davis Library.

    – By Jessica Nusbaum and Julia Ann Easley, UC Davis

  • Almond Orchard Recycling a Climate-Smart Strategy

    Recycling trees onsite can sequester carbon, save water and increase crop yields, making it a climate-smart practice for California’s irrigated almond orchards, finds a study from the University of California, Davis.

    Whole orchard recycling is when old orchard trees are ground, chipped and turned back into the soil before new almond trees are planted.

    The study, published in the journal PLOS ONE, suggests that whole orchard recycling can help almond orchards be more sustainable and resilient to drought while also increasing carbon storage in the soil.

    “To me what was really impressive was the water piece,” said corresponding author Amélie Gaudin, an associate professor of agroecology in the UC Davis Department of Plant Sciences. “Water is central to how we think about agriculture in California. This is a clear example of capitalizing on soil health. Here we see some real benefits for water conservation and for growers.”

     Burn vs. turn

    Drought and high almond prices have encouraged higher rates of orchard turnover in recent years. The previous practice of burning trees that are no longer productive is now restricted under air quality regulations, so whole orchard recycling presents an alternative. But how sustainable and effective is it for the environment and for farmers?

    For the study, scientists measured soil health and tree productivity of an almond orchard that turned previous Prunus woody biomass back into the soil through whole orchard recycling and compared it with an orchard that burned its old trees nine years prior. 

    They also experimentally reduced an orchard’s irrigation by 20 percent to quantify its water resilience.

    Their results found that, compared with burn treatments, whole orchard recycling can:

    • Sequester 5 tons of carbon per hectare
    • Increase water-use efficiency by 20 percent 
    • Increase crop yields by 19 percent


    “This seems to be a practice that can mitigate climate change by building the soil’s potential to be a carbon sink, while also building nutrients and water retention,” said Gaudin. “That can be especially important as water becomes more limited.”

    Study co-authors included Emad Jahanzad and Kelsey Brewer of UC Davis; Brent Holtz, Sean Hogan and Cameron Zuber of UC Agriculture and Natural Resources’ Cooperative Extension; and David Doll, who was formerly with UC Cooperative Extension.

    The study was funded by a Specialty Crop Block Grant Program of the California Department of Food and Agriculture and the Almond Board of California. — By Kat Kerlin, News and Media Relations, 530-752-7704, kekerlin@ucdavis.edu

  • Deciphering the Walnut Genome

    California produces 99 percent of the walnuts grown in the United States. New research could provide a major boost to the state’s growing $1.6 billion walnut industry by making it easier to breed walnut trees better equipped to combat the soil-borne pathogens that now plague many of California’s 4,800 growers.

    In a new study, a team of scientists at the University of California, Davis, and USDA’s Agricultural Research Service (ARS)used a unique approach to sequence the genomes of the English walnut and its wild North American relative by tapping into the capabilities of two state-of-the-art technologies: long-read DNA sequencing and optical genome mapping. The resulting genome sequences are believed to be of the highest quality ever assembled of any woody perennial.

    “By sequencing the genome of a walnut hybrid, we produced complete genome sequences for both parents in the time normally required to produce the sequence of one genome,” said Ming-Cheng Luo, leading genomics investigator on the project and a research geneticist in the Department of Plant Sciences at UC Davis.

    This approach could be applied to genome sequencing of trees and many other woody perennials, opening the door to a better understanding of the genetic blueprints of almonds, pecans, pistachios and grapes.

    “Like walnut, these other crops naturally cross-pollinate and are therefore highly variable,” said Jan Dvorak, co-principle investigator and genetics professor at the Department of Plant Sciences at UC Davis. “Variability has always greatly complicated our ability to produce a high-quality genome sequence for such crops, but these new technologies now make it possible,” Dvorak added.

    In California, walnuts are grown commercially using rootstocks chosen specifically for their ability to tolerate various soil-borne diseases.  “We chose to cross the widely used English walnut specifically with the wild Texas Black walnut because of its native resistance to several soil-borne diseases and root nematodes, which are serious pests of walnut in California” said Dan Kluepfel, a USDA-ARS scientist and principal investigator of the walnut-rootstock development project.

    The assembled genome sequences of the two walnut species also will now help researchers identify genetic markers that breeders can use to develop new varieties with improved pathogen and pest resistance.

    Major contributors to the project included UC Davis scientists Tingting Zhu, Le Wang, and Agriculture and Agri-Food Canada scientistFrank You.

    The study was published online today in Horticulture Research. The research was funded by the California Walnut Board and the USDA’s National Institute of Food and Agriculture Specialty Crop Research Initiative. The study can be found here.

    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.

  • Using the Sun & Agricultural Waste to Control Pests

    Biosolarization Shows Promise for Conventional & Organic Farmers

    By Diane Nelson

    Farmers spend a lot of time and money controlling weeds and other pests, and often have to turn to chemical fumigants to keep the most destructive pests at bay. Farmers also wrestle with what to do with low-value byproducts of crop production, such as skin, seeds and hulls from fruit, vegetable and nut processing.

    What if those agricultural waste streams could generate alternatives to chemical fumigants and make farming more productive, profitable and environmentally friendly?

    Maybe they can. Researchers at the University of California, Davis, are encouraged by early results from collaborative experiments with “biosolarization,” a process that combines the sun’s heat with soil amendments to manage weeds and other soil-borne pests.

    “It looks promising,” said food science and technology professor Christopher Simmons, who is testing biosolarization with various crops and working with farmers throughout the state. “We still have a lot of work to do, but biosolarization is showing real potential as a safe, sustainable way to control pests while improving crop quality and yield.”

    Strengthening solar power   

    Many backyard gardeners know the power of solarization. When you lay a clear plastic tarp over moist soil, you can trap solar radiation and heat the soil enough to kill weeds and other soil-borne pests. It’s effective, but can take four to six weeks, which is often too long for commercial fields to lay fallow.

    Biosolarization can accelerate and improve the process. Simmons and his team are adding organic amendments such as grape and tomato skins or ground nut hulls to the soil before they tarp it, which promotes growth of beneficial bacteria. The helpful microorganisms compete with pests and temporarily make the soil more acidic and therefore less hospitable to weeds and other pests.

    Together, the soil-heating and microbial activity can reduce the treatment time to days, not weeks.

    “And by activating beneficial microbes in the soil, biosolarization has the potential to improve soil health over the long term,” Simmons explained.

    Testing under commercial conditions

    Chemical fumigants are expensive, and many have been identified as carcinogenic by state and federal regulatory agencies. But when it comes to killing soil-borne pests, they are very effective.

    “Fumigants are broadly biocidal, meaning they affect beneficial microorganisms along with the pests,” Simmons said. “Biosolarization allows more innocuous and beneficial microorganisms to persist in the soil.”

    But for farmers to adopt biosolarization as an alternative to chemical fumigants, the treatment must be effective, predictable and economical. So the team is testing biosolarization with a wide variety of crops, amendments and soils against different pests in various locations at commercial scale throughout the state.

    “We have field trials underway with lettuce, tomatoes, melons and various cover crops,” Simmons said. “And we have a long-term, 10-acre trial with almonds at a conventional orchard in Chico.”

    In Chico, Simmons and his team are collaborating with almond grower Rory Crowley at Nicolaus Nut Company with funding support from the Almond Board of California and the Western Center for Agricultural Health and Safety. They are one year into a 25-year experiment to see if almond-processing residues and the sun can boost soil health and reduce weeds and other soil-borne pests. So far, Crowley is impressed.

    “It’s been great for the soil,” Crowley said. “Using biosolarization and a mustard cover crop, we’ve increased organic matter by 1.25 to 1.75 percent, which is a huge jump. That’s good for carbon sequestration and the overall health of the soil.”

    It’s too soon to tell if the soil improvements will translate to greater crop yield, but Crowley thinks biosolarization could become a good pest-management tool and a valuable use for what would otherwise be agricultural waste.

    “We need to find a home for the co-products of almond processing, so why not see if we can use them to improve soil health while controlling pests?” Crowley asks.

    Field tests continue

    Simmons and his team are testing biosolarization on several annual and cover crops in plots on the UC Davis campus using agricultural waste streams from tomato and wine processing. Soon they will begin tests with strawberries, which are commonly treated with fumigants each season as farmers plant berries anew.

    Simmons’ hope is to demonstrate to farmers that biosolarization can be effective and economical under a wide range of conditions against a broad number of pests.

    “We’re making significant ground,” he said. “We’re hopeful biosolarization can help farmers return food and agricultural waste back into the system to control pests and improve crop production.”