- Posted by: Gale Perez
Congratulations to UC Davis weed science graduate student Erika Escalona (Fennimore Lab) for winning 1st place in the student poster presentation category at the 2024 California Plant and Soil Conference on Feb. 6-7, 2024 in Fresno, CA.
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Evaluating Bacterial Diversity in Steam Fumigation Treatments in the Salinas Valley's Lettuce Fields
Erika Escalona, University of California, Davis; Steve Fennimore, UC Cooperative Extension, Weed Specialist, Salinas; Department of Plant Sciences, University of California, Davis; J.S. Rachuy, Department of Plant Sciences, UC Davis; Cristina Lazcano, Department of Land, Air and Water Resources, UC Davis
As the specter of climate change looms larger, sustainable and environmentally friendly alternatives for pest and pathogen control in agriculture are becoming increasingly imperative. Steam fumigation, once an antiquated method overshadowed by chemical pesticides, is experiencing a resurgence due to heightened environmental concerns. Despite its historical use, there has been limited exploration of scaling up steam fumigation for field applications in vegetable crops. Although existing studies have highlighted the efficacy of steam fumigation, a critical knowledge gap persists regarding its impact on the soil microbiome, a fundamental determinant of agricultural productivity. This study seeks to advance the validation of steam fumigation as a practical alternative to chemical fumigation by conducting a comprehensive assessment of vegetable productivity in lettuce and spinach grown in steamed soils versus non-steamed soils. The experiment utilized a custom-built steam applicator equipped with a low-pressure 1,000 kg/hour steam generator in Salinas, CA. All research and trials were conducted at the Salinas Extension and USDA Center. Soil samples were collected before and after steam application, and crops were meticulously monitored for disease and weed control, alongside yields at harvest. Preliminary results indicate effective weed control and increased yields in the presence of disease pressure. In addition to evaluating the efficiency of steam fumigation in weed and pathogen control, this study delves into a thorough investigation of the bacterial diversity of soils. The trials, conducted from July 2023 to August 2023, involved verifying the performance of the steam applicator, assessing beneficial soil organisms using 16S sequencing, and evaluating treatment impact on bacterial diversity. By examining the results obtained from these multifaceted trials, we aim to provide comprehensive insights into the overall effectiveness of steam fumigation and its potential application in sustainable agriculture practices, with a specific focus on its influence on the soil microbiome.
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To view the full story, visit UC Davis Plant Sciences Dept. News, Feb. 22, 2024.
Contacts
- Erika Escalona: eescalona@ucdavis.edu
- Steve Fennimore: safennimore@ucdavis.edu
Escalona-Erika24'UCANRconference
- Author: Trina Kleist
- Posted by: Gale Perez
AI-trained machines slash labor costs
Experimental robots are reducing the costs of hand-weeding by learning the difference between weeds and lettuce. In addition, steam can clear the soil of fungi and spores that cause lettuce and spinach to wilt, reducing the need for chemical herbicides in the bargain, according to the latest research by Steve Fennimore and his lab at the UC Davis Department of Plant Sciences.
Fennimore, a professor of Cooperative Extension, presented his findings at a recent meeting of the California Leafy Greens Research Board, a body of the state Department of Food and Agriculture, which is helping to fund the work. It was attended by growers, association representatives and educators. This research would help them solve three big problems:
“What everyone is facing is higher costs, fewer personnel and greater difficulty using pesticides due to regulations,” said Fennimore, who also is a specialist with UC Cooperative Extension.
He and team members Richard Smith (UCCE Farm Advisor) and Nelly Guerra (UC Davis Fennimore Lab graduate student) evaluated automated weeders that were trained using artificial intelligence for use in lettuce fields. In tests last year near Salinas, Calif., smart weeders built by FarmWise Labs Inc. and Stout Industrial Technology, Inc., removed between 32 percent and nearly 100 percent of purslane and other weeds, Fennimore said. That reduced the need for hand-weeding between 13 and 62 percent. The weeders proved more cost-effective in fields where there were more weeds, Fennimore added.
The team also tested steam to clear soil of diseases that cause leafy greens to wilt and turn brown at the edges. During trials last summer in the Salinas Valley and in Yuma, Ariz., team members measured soil pathogens before and after steaming the rows where seed is planted. They found significant reduction in the fungus fusarium; in the tiny balls, or microsclerotia, that allow fungus to survive in the soil; and in pythium, a water-born mold. Steam treatments also boosted lettuce yield and reduced weeds. The team collaborated with Mark Siemens, of the University of Arizona.
Building on those successes, Fennimore and team this year are combining steam with standard cultivation to see if they can control weeds 100 percent and reduce hand-weeding to zero.
Media resource: TrinaKleist, tkleist@ucdavis.edu, (530) 754-6148 or (530) 601-6846
Original source: UC Davis Plant Sciences Dept. website
- Author: Bob Johnson
- Posted by: Gale Perez
From the weekly newspaper for California Agriculture, Ag Alert • Dec. 2, 2020 • California Farm Bureau Federation
Advisors seek practical use of steam in weed control
By Bob Johnson
Steam-treating a shallow band of soil within the seed line before planting may offer, when combined with advanced cultivators, an economical weed control option for organic farmers and conventional growers looking to reduce herbicide use.
University of California specialists said their research in Salinas Valley vegetable fields this year showed the technique can significantly reduce weed pressure and hand-weeding time, and even produce larger and more vigorous lettuce plants.
"We're reducing the hand-weeding time," UC Cooperative Extension weed specialist Steve Fennimore said. "The plants were larger, significantly larger."
Fennimore, who has been studying steam as a way to control weeds and soil diseases since strawberry growers first faced the loss of the fumigant methyl bromide, presented his latest research during the UC Online 2020 Pest Management Series in early November.
Steam works as well as fumigation in reducing weeds and soil-borne disease pressure, he said, but previous efforts have shown that treating the entire bed can be too expensive and time-consuming to be practical in most situations.
"With banded steam, you treat less of the bed," Fennimore said. "Our target would be to heat the soil to about 150 degrees Fahrenheit; but you would only need to steam 2 or 3 inches deep. Then you could seed lettuce in the seed line and cultivate outside of it."
Fennimore and UC graduate research fellow Nelly Guerra tested steam this year in three Salinas Valley trials—two on lettuce and the third on spinach—as they compared weed pressure after steam-treating the seed line with and without hydrogen peroxide, an organically approved compound that helps spread the heat.
The researchers said banded steam showed similar efficacy in the second lettuce trial, reducing nightshade and shepherd's purse by 75% to 90%, and significantly reducing little mallow when the hydrogen peroxide was added to the steam.
The steam treatment reduced hand-weeding time by 20% to 40%, and reduced lettuce-drop damage by 54% to 67%, they said.
Another set of Salinas Valley vegetable trials showed the promise of GPS-controlled, autonomous weeders that cultivate without a driver, outside and within the seed line.
"This project comes down to labor," said Elizabeth Mosqueda, weed science professor at California State University, Monterey Bay. "It takes a lot of manpower to remove weeds from one lettuce field. How can we decrease labor costs in leafy green production? The other part of this is the number of herbicides available; the last formulation for lettuce was introduced in 2014."
Mosqueda tested two autonomous weeders in Salinas-area commercial lettuce fields: the relatively small DINO weeder from France and the larger Farmwise Titan robotic weeder.
"Both of these companies want to get to the point that one operator can be in the field with multiple machines," Mosqueda said. "But autonomous weeders can already weed between and within rows at the same time."
The time saved by using the autonomous weeders that cultivate within the rows varied with the amount of weed pressure in the three fields where they were tested, she said: Field one had exceptionally light weed pressure, and the autonomous cultivators did not save hand-weeding time. But in field two, with higher weed pressure, hand-weeding time was reduced from 11.1 hours per acre to 9.4 hours. The greatest reduction in hand-weeding time, from 16.9 hours to 9.9 hours, came in the most heavily infested third field.
"Our autonomous weeders controlled about 85% of the weeds, compared to 40% with a standard cultivator," Mosqueda said. "The uncultivated seed line is the area of concern. Weeds between the plants are typically removed by hand."
Although advanced cultivators may be the answer to more effective control of weeds after they emerge, Fennimore said steam could become a more economical method of preventing emergence.
"How do you get pre-emergent weed control that is compliant with organic regulations?" he asked. "Steam is the oldest method of soil disinfestation. The guys in Denmark have shown it can be an economical method of weed control."
Treating just a shallow, narrow band of soil within the seed line makes steam more affordable, but Fennimore said he hopes to go even further in reducing the time, fuel and money needed to use steam.
"Spot steaming is something I would like to try," he said. "You could do a 4-inch square and plant a vegetable in the spot. You would need precision equipment. We want it to be the cheapest; we want to go faster and use less fuel."
The steady growth of organics in strawberries has taken Fennimore back to the question of how to treat the soil before planting the crop.
"The hand-weeding costs in organic strawberries have gone up a lot; it's up to $3,700 an acre," he said.
Fennimore did a series of steam trials at a strawberry nursery in the mountain region near the Oregon border, and in commercial fields in the Watsonville-Salinas area.
He said steam with or without mustard meal was as effective as fumigation with chloropicrin in ridding soil of Verticillium wilt pathogens, and yields were comparable to fumigated plots.
One promising insight coming from the trials, he said, is it looks as though steam and mustard meal have a synergistic effect when used together.
"The steam looks like it releases biofumigant compounds from the mustard meal," Fennimore said.
(Bob Johnson is a reporter in Sacramento. He may be contacted at bjohn11135@gmail.com.)
Original source: California Farm Bureau Federation's Ag Alert newsletter
/h2>- Author: Nelly Guerra
- Author: Steven Fennimore
Despite the tremendous need, there are currently no preemergence herbicides that are organic-compliant. Steam injected into the soil such that the soil temperatures reach >140°F for 15-20 minutes will kill weed seed in the soil. The effect of this reduction in the seedbank viability results weed control in the treated area that persists for several weeks or months, similar to the effects of a preemergence herbicide.
We are not aware of any commercial scale applicators for lettuce that apply steam in a band to the lettuce bed. However, we are working with Dr. Mark Siemens, an agricultural engineer with the University of Arizona to design a commercial scale applicator. Mark has a prototype applicator built and will be demonstrating it during the winter season in the Yuma Valley. It appears that the design for a steam applicator is not complicated and is well within the capabilities of machine shops in California to build.
- Author: Mark Bolda
Uh... no I don't think so. Not by a long shot.
Consider the loosely written article from WaPo concerning the phase-out of methyl bromide and the effect it will have on the strawberry industry:
http://www.washingtonpost.com/news/speaking-of-science/wp/2015/08/04/scientists-race-to-find-solution-for-imperiled-strawberry-industry/
Yes, beyond the breeding, steam and ASD, actual methyl bromide fumigation alternatives do exist and will play a big role in the future of the industry. Matter of fact, I've a got a meeting going on this afternoon at my office of top industry scientists and growers to coordinate our efforts in just that.
Money line of the article by UCCE scientist Steve Fennimore - "People talk about a silver bullet to replace it, and that's a mistake. We want to put a lot of treatments together and make it all work."