Posts Tagged: fumigant

Alternatives to fumigation and improving fumigant efficacy

Synthetic soil fumigants such as chloropicrin and 1,3-D are used by some commercial growers to control soilborne pathogens, weeds and nematodes prior to planting strawberries, onions, tomatoes, eggplant, peppers and spinach. These fumigants and all other biocidal products with the potential to harm the environment and human health are highly-regulated by the federal Environmental Protection Agency, the state Department of Pesticide Regulation, and county agricultural commissioner's offices.

UC Cooperative Extension farm advisor Oleg Daugovish and his collaborators work hard to find effective, environmentally-safe and economically-viable ways to improve efficacy of fumigants and to investigate alternatives to soil fumigation. The Ventura County Cooperative Extension website has archived audio and visual presentations, which includes the following topics:

• Assessment of permeability of commercial tarps under a variety of cultural practices and in various soil and environmental conditions is expected to lead to better understanding of maximizing fumigant effectiveness while reducing emissions.

• Growing in substrate (soil-less culture) allows growers to produce crops with minimal plant disease and weeds without using fumigants.

• Heating soil using steam is a successful way to disinfest it. However, the process to generate steam in a field can be slow and very expensive. Researchers are working to find ways to improve speed while reducing cost.

• Most organisms, including plant pathogens, cannot survive without oxygen. Researchers are investigating an organic method to create anaerobic (oxygen-free) conditions to treat soil before planting.

• Planting mustard as a cover crop can provide many positive benefits, one of which is allelochemical compounds. These compounds found in mustard are similar to those found in fumigants. Current research shows it is possible to use this green biomass to prepare fields for production.

More environmentally-responsible research from Dr. Daugovish can be found here.

Injecting steam may be one way to disinfest soil without chemical fumigants.

Strawberry fields forever

Methyl iodide – yes, that volatile chemical that could find use as a soil fumigant – has been in the news lately, and mostly in a negative light. In April, California’s Department of Pesticide Regulation made a preliminary decision to approve the use of methyl iodide as a fumigant under strict conditions, and soon after received more than 50,000 public comments.

Methyl iodide, it turns out, is not only toxic, like all fumigants, it “can cause cancer, brain damage and miscarriages.” Its potential use in California’s strawberry fields in place of its ozone-depleting and toxic cousin, methyl bromide, is what shot the compound into news orbit.

Why phase out methyl bromide as a soil fumigant? Answer: Ozone loss up in the stratosphere, leading to more ultraviolet light penetrating the Earth’s atmosphere, leading, in turn, to increases in skin cancer. When methyl bromide is released in the lower atmosphere, a fraction gets transported into the stratosphere where it undergoes a series of chemical reactions leading to stratospheric ozone depletion.

Cousin methyl iodide, on the other hand, is photolyzed quickly in the lower atmosphere, leaving none of it to escape into the stratosphere.

While public opinion currently leans heavily against the use of methyl iodide as a soil fumigant replacement, James Sims, a professor emeritus of plant pathology at UC Riverside, supports its use.  For one thing, it delivers results similar to methyl bromide, he says, and, second, it can be used safely. He explains that it is not applied directly to plants; it is injected into the soil two weeks before any plants are planted.

Methyl iodide is a liquid boiling at 42.5 degrees C or 108.5 degrees F. Sims says it is therefore safer for workers to handle than a gas like methyl bromide. Moreover, it can be applied using the same equipment with few or no modifications, and it is effective in reducing pest, weed and plant disease problems. Other alternatives — solarization, anaerobic soil disinfestations, crop rotation, steaming, etc. — are not effective, Sims says.

Critics are not convinced of methyl iodide’s relative safety and growers, meanwhile, continue to insist that their fields need a fumigant that poses no harm to our precious ozone layer.

How then might the controversy play out? We will have to wait and see – for several weeks at least. After processing the public comments received, state officials plan to weigh in on the “controversial effort to register the fumigant methyl iodide.”

UC specialist looks into steam cleaning soil

UC researchers are considering the use of hot steam fumigation on coastal central California farms to prepare soil for planting strawberries and new orchards and vineyards. Farmers there have for years relied on methyl bromide, but the phase-out of the powerful soil fumigant is closing in, according to an article in The Packer.

To study the steam method, UC weed specialist Steve Fennimore outfitted a tractor with a boiler that heats steam to more than 300 degrees F. Ten-inch spikes inject steam into the ground.

The article, written by Elizabeth Ashby, said sandy or light soils are the easiest to treat, but Fennimore has had success in clay loam in Watsonville, Calif.

“This machine…there is something special about it,” Fennimore was quoted in the story. “It is surprising how fast it heats the soil. Within two minutes, it will take 60-degree soil and heat it to 200 degrees. It is like a microwave.”

The quick-acting treatment allows growers to steam in the morning and plant that afternoon when the ground has cooled. That stands in contrast to soil solarization, another possible methyl bromide alternative. Under the solarization system, the field is covered with plastic and the sun heats the soil and kills pathogens. Solarization takes six weeks.

One drawback of the steam system, however, is cost. Fennimore calculated that operating the steam machine, labor and fuel run $4,200 per acre. Methyl bromide in California costs $2,700 to $3,000 per acre. Applying steam to raised beds rather than entire fields could cut expenses to about $3,000 per acre.

Future studies will examine less expensive fuels like propane, ways to speed up the steam injection process and spot treatments.

UC specialist Steve Fennimore is studying steam soil treatment.

Scientific panel suggests state ban methyl iodide

The Fresno Bee ran a story on the front page this morning reporting that a scientific panel recommended that the California State Department of Pesticide Regulation reject a request by Tokyo-based Arysta LifeScience Corp. to approve the use of methyl iodide for pest control on California farms and in structures.

The eight-member Scientific Review Committee, chaired by UCLA environmental health sciencies professor John Froines, includes UC San Francisco medicine professor Paul Blanc, UC Berkeley public health professor Katharine Hammond and UC Berkeley environmental health sciences professor Tom McKone.

Methyl iodide was approved by the U.S. Environmental Protection Agency and many other states, but if California rejects the use of the pesticide, the U.S. EPA "may choose to initiate reevaluation of the methyl iodide registration," according to the panel's report to DPR.

"Based on the data available, we know that methyl iodide is a highly toxic chemical and we expect that any anticipated scenario for the agricultural or structural fumigation use of this agent would result in exposures to a large number of the public and thus would have a significant adverse impact on the public health," the panel wrote.

Farmers, however, believe methyl iodide would be an important tool in their arsenal for controlling soil pests in nursery containers and in the field before planting strawberries or establishing new orchards. The chemical could replace methyl bromide, which has been phased out because it damages the Earth's ozone layer.

"The products that we have just don't do the job," Bee reporter Robert Rodriguez quoted Barry Bedwell, president of the California Grape and Tree Fruit League.

According to the Bee article, DPR director Mary-Ann Warmerdam will review the panel's findings and DPR research as she decides if farmers can use the chemical and if so, under what restrictions. The decision is expected "soon."

The UC Integrated Pest Management Program has reported that soil solarization may be an alternative to chemical soil pest control under the right weather conditions. More information is available on the UC ANR Methyl Bromide Alternatives Web site.

Soil solarization is a possible alternative to methyl bromide fumigation.

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