- Author: Marcelo Moretti
- Posted by: Gale Perez
From the Weeders of the West (WoW) blog ∴ March 11, 2021
Marcelo Moretti is a Professor in the Dept. of Horticulture at Oregon State University and an alumnus of UC Davis and California State University, Fresno.
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Managing Herbicide Resistance with Electric Weed Control
Herbicide resistance has also been a problem in tree nut crops for quite some time. In hazelnuts in Oregon, the most problematic herbicide-resistant weed is Italian ryegrass. Resistance is now confirmed to herbicides in groups 1, 2, 9, 10, 15, and 22. Resistance to more than one mode-of-action is often found in the populations. Non-chemical alternatives are needed. We recently started a project to evaluate electric weed control (EWC) funded by USDA – Crop Protection and Pest Management program.
Electric weed control (EWC) has been investigated for almost 40 years. However, it remains an emerging technology in the USA and elsewhere in the world. A few companies, mostly in Europe and Latin America, offer commercial EWC units. In Oregon, we initiated our work on EWC only this morning! Assembly details and small changes required a couple of weeks to resolve, but now we are ready to start EWC trials in Oregon for 2021. We are collaborating with Zasso (Indaiatuba, Brazil), working with an EH30 Thor unit (Figure 1).
How it works
The system generates a high voltage current that is applied directly to the plant via foliage contact with a metal bar. The voltage is conducted through the plant towards the roots. As high voltage passes through the plant, electrical resistance generates heat, leading to cell membrane rupture and plant death. Watch a short YouTube video of the process.
Power requirement
A PTO-driven generator produces electricity. A transformer increases the generator's voltage to 5,000-12,000 V. Tractor horsepower, and EWC unit configuration controls the voltage. The unit requires at least 75 hp power at the PTO, but I am inclined to say that you may want a bit more in wet soils with high clay content soil.
Acknowledgments
The USDA Crop Protection and Pest Management Program funds this work (award no. 2020-70006-32982). I would also like to acknowledge the Oregon Hazelnut Commission's support and the local growers who will participate in this project.
Original source: Weeders of the West (WoW) blog ∴ March 11, 2021
- 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: Margaret Gullette Lloyd
- Re-posted by: Gale Perez
From the Small and Organic Farm Advisor Blog
Johnsongrass in organics: Mow it?
Yes, mow it! Mowing works to at least prevent seed spread and regular mowing will weaken rhizomes.
Seed establishment has the greatest potential for the establishment and spread of johnsongrass and must be prevented. Therefore, mowing works to at least prevent seed spread. An individual plant can produce 28,000-30,000 seeds and a single inflorescence can measure 1,240 seeds (Keeley and Thullen, 1979). Viable seed may be produced as early as 2 weeks after flowering begins, so timely control measures throughout the season are needed to prevent seed production. Even though the viability of johnsongrass seed in soil remains high for as long as five years, seed can remain viable in soil up to 10 years.
Regular mowing can be effective in both orchard and non-crop situations. Due to its capacity to regenerate from rhizome fragments, complete control of S. halepense by mowing alone is difficult. Nonetheless, intensive grazing and mowing can be used to reduce a stand of johnsongrass. If grazed or mowed closely for at least two years, the plants become weak and stunted and the rhizomes become concentrated near the soil surface.
Consider mowing johnsongrass stands before seeds set to weaken current stands and avoid the spread through seed dispersal.
REFERENCE
P. E. Keeley, & R. J. Thullen. (1979). Influence of Planting Date on the Growth of Johnsongrass (Sorghum halepense) from Seed. Weed Science, 27(5), 554-558. Retrieved June 30, 2020, from www.jstor.org/stable/4043118.
Original source: Small and Organic Farm Advisor Blog
- Author: Pratap Devkota
As we are in the mid-summer, many fields in the low desert region are preparing for soil solarization. Soil solarization is a widely adopted pest control method by organic growers in the low desert region. With the increase in organic production acreage in recent years, we are seeing more fields implementing soil solarization during summer.
Soil solarization is a method for controlling soilborne pathogens, insects, nematodes, and weed seeds & seedlings by disinfesting soil by the solar heat. Solarization is implemented during summer months, where soil is heated by covering with transparent polyethylene mulch/tarp. The plastic covering permits solar radiation/energy to penetrate and trap in the soil; thereby, building heat in the soil (Fig 1). The higher temperature disinfects soil and provides pest control. Moisture is also important component for soil solarization because wet soil is better conductor of heat than dry soil.
There are four important considerations for soil solarization.
- Field preparation/cultivation and removal of clods and plant debris that might hinder soil solarization
- Listing soil beds (north to south bed orientation is desired)
- Irrigation of soil beds (soil moisture 75% or greater of field capacity)
- Laying out the plastic sheet on the beds (beds are covered with plastic sheets for about 4 to 6 weeks)
Clear or transparent plastic sheet is most effective for solarization, because it allows the entry of solar radiations to the soil bed (Fig 2). Colored-plastic sheet is less effective because they reflect light and solar radiation does not penetrate through as effectively as in the clear plastic sheet. Plastic sheets are found in various thickness and selection has to be made appropriately. Thin plastic sheet (1 mil) provides greater heating but is also more susceptible to tearing during lay out or later from wind pressure. Slightly thicker plastic sheets (1.5 to 2 mils) is advantageous for windy conditions (FYI, 1 mil = 0.001 inch or 0.025 mm).
Weed control
Soil solarization is found to be effective in controlling various annual weeds. Some weed species are highly sensitive to solarization while other species are moderately sensitive to less sensitive. In general, winter annual weeds are more sensitive to soil solarization compared to summer annuals. Likewise, weeds with hard seed coat are less sensitive to soil solarization. Some of the weed species found in low desert region, such as common purslane, nettleleaf goosefoot, little mallow, littleseed canarygrass are less sensitive to soil solarization (Fig 3). For the perennial weed species such as nutsedge spp., johnsongrass, and bermudagrass soil solarization controls their seeds but has less effect on perennial structures such as tuber, rhizome, and stolon. Solarization is less effective on perennial structures buried deep into the soil (> 6 inches deep).
For more information on soil solarization, here is a good publication from UC Vegetable Research and Information Center.
- Elmore, CL, JJ Sapleton, CE Bell, and JE Devay (1997) Soil Solarization: A Nonpesticidal Method for Controlling Diseases, Nematodes, and Weeds. UC Vegetable Research and Information Center. Available at: http://vric.ucdavis.edu/pdf/soil_solarization.pdf
- Author: Cheryl A. Wilen
A few months ago I wrote about starting some tests looking at various postemergence herbicides for non-crop use, (see Just started new tests of contact herbicides). This project was initiated due to new ordinances some cities in southern California were considering or adopted that limited the use products containing glyphosate on city owned property. I changed up some of the products from the original test I did and repeated some others.
Some are listed as organic and some are organic but not be organically approved by a certifying agency e.g. OMRI. One is listed as a biopesticide (Fiesta). One is a synthetic pesticide (Finale) that may be a good replacement in certain situations.
The treated areas (4x10') were divided into 3 parts. The front 4x5' section was treated with the herbicide two times. The back 4x5' section was split into two 2x5' sections. The left section was treated with the herbicide + 0.5% Liberate surfactant and the right side was left as an untreated check. This was done to account for any differences in weed species in each plot.
I used 90GPA spray volume at 40PSI using a flat fan nozzle. Most weeds were under 5” when the treatments were first applied but escapes were larger by the second application. Most plots had hairy fleabane, horseweed, annual sowthistle, Jerusalem oak, and common purslane.
While I'm still evaluating the data, I can say that some products look pretty good and while the costs are high (see Table 1), at least the cities can narrow down what products would work for them.
Just considering overall weed control, my observations are that FinalSan+Liberate; WeedPharm (or any 20% acetic acid) with or without surfactant; Suppress; and Finale have the best potential. While 3 of the 4 products are organic, note that all are more hazardous than Roundup per the signal word. Fiesta provided excellent control of hairy fleabane, horseweed, and annual sowthistle, especially when the surfactant was included. Because seedlings emerged after treatments, they contributed to the overall weed pressure. In the best scenario, these materials would be applied with a preemergent herbicide to suppress weed germination. This would likely reduce cost of the postemergent treatments as well as labor costs.