- Contributor: Marcelo Moretti
- Contributor: Inga Zasada
- Contributor: Jerry Weiland
- Contributor: Tatiana Benedetti
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I'll share some initial findings from our project, which explores the use of pulse electric fields to eliminate soil pests in hardwood nursery beds, with a particular focus on the impact on weed populations.
Pulse Electric Field as an Alternative to Methyl Bromide
Methyl bromide, a broad-spectrum pesticide for soil disinfection, weed control, and soilborne fungi and nematodes management, is also notorious for its ozone-depleting properties. Consequently, its usage in agriculture has been progressively phased out. Though some essential applications persist, the increasing costs and stringent regulatory standards have made it a less practical choice for pest control.
Pulse Electric Field (PEF) – A New Approach
Pulse electric field (PEF) employs bursts of high-voltage electricity to deactivate microorganisms (see Figure 1). Although primarily utilized in the food industry, there have been encouraging reports of its effectiveness in controlling nematodes and plant diseases (Riga et al., 2020). In our collaboration with Lisi Global, we are adapting this technology for a novel application within the ornamental nursery industry.
The precise mechanism by which PEF eliminates organisms remains a subject of ongoing study. It may involve cell membrane rupture, accompanied by metabolic shutdown, or the absorption of energy by specific proteins leading to the generation of cell-damaging free radicals. Alternatively, protein structures may be altered, rendering them non-functional. The non-thermal nature of PEF is generally accepted, but the results may vary depending on the energy applied to the soil.
Treating Soil with PEF
Treating soil with PEF involves sandwiching soil between two electrodes for the required duration to deliver the desired energy. The goal is to maintain a high voltage current between the electrodes. In the short term, energy is stored briefly in a capacitor, and factors like voltage, pulse number, duration, and frequency can be adjusted to control the energy delivered. The distance between electrodes also impacts PEF performance, as the soil's resistance affects the flow of current.
Impact of PEF on Weeds
Surprisingly little is known about the effects of PEF on weeds, prompting us to initiate pot studies to determine effective rates. Controlled greenhouse experiments help eliminate the variability often encountered in the field and provide a solid starting point for treatment guidelines. For reference, a previous study (Riga et al., 2020) demonstrated that 25 J cm^-3 could control over 90% of nematodes. In our experiments, 480 J cm^-3 produced enough energy to generate heat, water vapor, and even melt the pots (see Figure 2), challenging the notion that PEF cannot be a thermal soil sterilant.
https://youtu.be/SV9zoXpvn84?si=RQh_ctDkIR-jD3ZL
For weeds, electrical rates of 60 J cm^-3 or higher effectively eliminated nearly all yellow nutsedge tubers, although a few crabgrass plants did emerge after treatment with 125 J cm^-3. We are currently expanding our research to other weed species and exploring methods to enhance efficacy. Our ultimate goal is to determine the minimum energy required to consistently control a mixture of weed species.
The Next Step: Field Validation
This autumn, we will commence field studies in collaboration with Oregon nurseries. We are pushing ahead on multiple research fronts as we pioneer this new application for PEF. The development of new technology is invariably challenging and resource-intensive. Adapting existing technology to a new purpose presents multiple hurdles, with one significant challenge being that the energy levels required for soil disinfestation exceed the original equipment design limits. This places substantial strain on the batteries, cooling system, and electronics, all of which have pushed the boundaries of their capabilities.
Acknowledgments
This project is generously funded by the USDA-NIFA Methyl Bromide Transition Program (2022-51102-38259), the Horticulture Research Institute, and the Oregon Association of Nurseries. We extend our sincere gratitude to our collaborators, J. Frank Schmidt & Son Nursery in Boring, OR, and Robinson Nursery in McMinnville, OR, without whose support this work would not have been possible.
Reference
Riga, E., Crisp, J.D., McComb, G.J., Weiland, J.E. and Zasada, I.A., 2020. Directed energy system technology for the control of soilborne fungal pathogens and plant?parasitic nematodes. Pest management science, 76(6), pp.2072-2078.
Original source: Weeders of the West blog ¦ Nov. 9, 2023
- Author: Pamela Kan-Rice
- Author: Jim Downing
2016 is the final year for the soil fumigant to be used in California crop fields.
For many years, California growers relied on methyl bromide to kill a wide range of soil-borne pests, from fungi to insects to weeds, before planting crops. 2016 marks the last year in which the highly effective soil fumigant will be available.
The University of California's peer-reviewed journal California Agriculture examines the impact of the methyl bromide phaseout on strawberries, California's third most valuable crop, behind only almonds and grapes, with annual farmgate sales of $2.5 billion.
First identified as an ozone-depleting compound in 1991, methyl bromide was scheduled for phaseout in the United States by 2005 under the Montreal Protocol, an international agreement to protect the stratospheric ozone layer.
While methyl bromide was used for many crops, California strawberry growers found it irreplaceable, which helped the industry win exemptions that have allowed a significant, though declining, quantity of the chemical to be used through 2016. Despite years of research into alternatives, no equally effective replacement has emerged.
Berry industry grows dramatically
In the first research article, UC Cooperative Extension advisors Laura Tourte and Mark Bolda and Karen Klonsky, emeritus UC Cooperative Extension economics specialist, review economic data on the berry sector — blackberries and raspberries as well as strawberries — in Santa Cruz and Monterey counties. They look ahead to factors, including water, consumer demands, labor, invasive pests, and the full phaseout of methyl bromide, that are likely to shape future growth.
Methyl iodide controversy
In a paper chronicling events leading up to the 2012 withdrawal of methyl iodide, once promoted as a viable methyl bromide substitute, Julie Guthman, UC Santa Cruz professor in the Department of Social Sciences, reports survey findings that point to a variety of reasons why strawberry growers did not move quickly to adopt the chemical after it was approved by state regulators. Concerns about public opposition topped the list, followed by a variety of other factors, including concern about methyl iodide's toxicity, and a lack of strong incentive to switch to the new chemical because of the availability of other fumigants, including methyl bromide.
Managing soilborne pests
Three articles look at new approaches to managing soilborne pests without methyl bromide.
“It now seems likely that no single measure will suffice to meet the challenge of soilborne pathogens,” write Margaret Lloyd, UC Cooperative Extension advisor, and Tom Gordon, UC Davis professor in the Department of Plant Pathology, in this issue's Outlook. “Rather, a multi-faceted approach will be required, one that integrates advances in disease resistance through breeding with closer attention to the factors that influence the survival, activity and spread of pathogen populations in soil.” They make the case for using a suite of strategies to manage soilborne pathogens — including collective action among growers to help limit the spread of pathogens between fields.
A news item on research at the UC ANR Hansen Agricultural Research and Extension Center covers ongoing research on anaerobic soil disinfestation, a chemical-free technique that is being used in a growing number of commercial fields. Project scientist Amanda Hodson and UC Davis professor Edwin Lewis, both in the Department of Entomology and Nematology, review a variety of approaches to managing for soil health — in strawberries and other crops — as a pest suppression strategy.
Other soil fumigants
Fumigants other than methyl bromide, such as chloropicrin, remain widely used in California strawberry production. Rachael Goodhue, UC Davis professor in the Department of Agricultural and Resource Economics at UC Davis, examines how increasingly stringent buffer zone requirements for chloropicrin application have an uneven impact on growers, depending on their proximity to developed land. In another article, a group of UC Cooperative Extension and U.S. Department of Agriculture scientists report on the effectiveness of several fumigants at dosages lower than the maximum label rate.
Food safety and nutrient management on the farm
The issue also includes two research papers focused on general production practices for crops. One report discusses on-farm food safety practices based on a survey of produce growers. The researchers found that practices such as exclusion fencing and vegetation clearing, which may negatively impact wildlife, remain widespread despite a lack of clear evidence that they enhance food safety. Finally, Daniel Geisseler, UC Cooperative Extension specialist in the Department of Land, Air and Water Resources at UC Davis, and Gene Miyao, UC Cooperative Extension advisor, review the use of soil testing to guide the management of soil phosphorus and potassium in California cropping systems.
To read California Agriculture, a peer-reviewed journal of research in agricultural, human and natural resources published by UC Agriculture and Natural Resources, visit http://calag.ucanr.edu. For a free subscription, sign up on the website or write to calag@ucanr.edu.
View this story in Spanish:
¿Qué hará la industria de la fresa sin el bromuro de metilo? http://ucanr.edu/sites/Spanish/noticias/?uid=6887&ds=199. Video on UCANR Spanish YouTube: California Agriculture: el bromuro de metilo en cultivos de fresa https://www.youtube.com/watch?v=5D4FwLqjaLk.
- Author: Mark Bolda
Pretty short notice here, but UCCE's own Steve Fennimore is giving a seminar on the transition from methyl bromide to alternative pre-plant treatments in strawberry. It will be conveniently webcast, see the information on the flier below.
I'm tuning in for sure, I want to hear from a researcher who actually has spent a lot of time with this stuff in the trenches.
- Author: Jeannette E. Warnert
Methyl bromide use has dropped dramatically over the years and is expected to be completely phased out by 2016, but strawberry farmers still don't have an alternative that works as well. Research is continuing.
"We're going to be using fumigants for a long time," said Steven Fennimore, UC Agriculture and Natural Resources Cooperative Extension specialist based at the USDA ag research station in Salinas. "They're relatively cheap and going all organic exposes you to a lot of pests."
Among the possible solutions shared in the Washington Post are:
- Finding and developing genetic resistance in strawberries to soil-borne diseases
- Anaerobic soil disinfestation, where a soil environment is created that is toxic for plant pathogens
- Steam injection
Fennimore suggests that there is unlikely to be a single tactic to replace methyl bromide.
"People talk about a silver bullet to replace it, and that's a mistake," Fennimore said. "We want to put a lot of treatments together and make it all work."
- Author: Aubrey White
Writing on Earth Day, I am reminded of one of the world's major successes in environmental protection, the Montreal Protocol. Originally signed in 1987, it works to phase out ozone-depleting substanc
Twenty-seven years later, the realities of enacting the Montreal Protocol are still taking shape, and strawberry growers are, with each harvest year, a step closer to a complete phase out of the fumigant and increased restrictions on alternative chemical fumigants used for disease suppression.
UC research has focused on how to make an economically viable and effective transition away from the soil fumigant. Initial alternatives include replacement chemical fumigants as well as biological fumigants such as anaerobic soil disinfection (such as putting tarps over fields to decrease oxygen), mustard seed meal amendment, or steam disinfestation.
But what if a practice many growers already use could also serve to suppress soil-borne diseases? What if growers could use a substance that provides multiple on-farm benefits?
Many conventional and organic growers alike use compost to boost soil fertility and organic matter. But compost's potential to serve other purposes, including suppressing disease, remain largely unexplored.
Ph.D. student Margaret Lloyd and Tom Gordon, professor in the Department of Plant Pathology at UC Davis, are hoping to close the gap in that knowledge. With a grant from the National Strawberry Sustainability Initiative, a program administered by University of Arkansas and funded by Walmart Foundation, and funding from UC Sustainable Agriculture Research and Education Program, Lloyd's research seeks to understand whether compost can contribute to disease suppression on a commercial scale, and how growers can best incorporate compost into their farm management to see its benefits.
“Compost is part of the production system that has potential as biological control,” says Lloyd. “Historically, we've only focused on it as a source of organic matter or soil nutrients. I'm trying to characterize its role in root health and soil health.”
The study evaluates the root health of strawberry plants, and compares plant yield and disease suppression across a number of research sites and compost types.
“In general, we talk about compost just as compost,” Lloyd said. “But it has drastically different qualities — soil fertility characteristics, physical properties, and microbial profiles. By focusing on different compost sources, the study will help growers better assess their available compost options to m
Alternatives to methyl bromide have been a long time coming. “The research suggests that it won't be one technology replacing another, but a package of tools to help growers manage disease suppression in the soil,” Lloyd said. If some of those tools are already in a grower's tool kit, the transition away from fumigants will be that much smoother.
The research suggests a powerful Earth Day message for me: use what you have, but seek a deeper understanding of just how to use it.
Lloyd's research findings will be completed in 2014, with results available for growers in 2015. Visit the project's website for more information.