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Life after methyl bromide: methyl bromide is one of the top five most widely used pesticides in the world.

Eighty seven percent of methyl bromide is used by farmers prior to planting to eradicate fungus, weeds, and microorganisms from the soil to avoid destruction to the crop. In the United States, it is used primarily for tomato, strawberry, and bell pepper crops. The problem is--and according to a recent United Nations report--methyl bromide depletes the ozone. The phase out of using this soil fumigant can be seen as going too slow for some, but others want to wait for the right alternatives.

Exemptions for 2005 were granted to the United States and ten other countries last year through the international conference in Prague, called the Montreal Protocol. Final 2006 exemption amounts for the United States will be decided at a special meeting of international technical experts in late 2005.

The chemical is used to kill nematodes, pathogens and weeds in soil before planting and as a post-harvest insecticide on stored grain, nuts and fruits. Critical use exemptions (CUEs) are allowed when no technically or economically feasible alternative exists, or when the ban would cause economic disruption. The 9,445 metric ton U.S. exemption for 2005--mostly for tomato, strawberry, cucurbit and pepper growers--is seven percent more than that used in the United States in 2003.

The issue of methyl bromide

While environmentalists are concerned that methyl bromide use in the United States is on the rise, farm-based organizations are disturbed that exemption requests for 2006 have been cut. But despite delays in a full transition to methyl bromide replacements, largely connected with safety and economic concerns, many growers are already working with a combination of alternatives. Last fall, farmers, regulators, food processors, and researchers shared their results at the Fifth International Conference on Methyl Bromide Alternatives in Lisbon and at the Annual International Research Conference on Methyl Bromide Alternatives and Emission Reductions in Florida.

"We have worked out some very good alternative control tactics using EPA registered products, which provide efficacy and harvestable yields statistically comparable to methyl bromide in almost all trials," says Jack Norton, manager of the Interregional Research Project No. 4 on methyl bromide alternatives. "However there are some issues associated with the use of those products which impose some additional risk on our growers, especially in Florida."

Treatments that have shown promise as alternative soil fumigants are Telone C-35 or InLine, an emulsified version that can be drip applied. The active ingredients in both products are 1, 3-dichloropropene (1, 3-D) which kills nematodes and chloropicrin, which prevents disease. When applications are followed with metam sodium or metam potassium they provide pest control and harvestable yields comparable to methyl bromide according to Norton and other researchers. But a significant potential drawback to commercial application is a shortened planting "window" since the combined applications require growers to wait almost four weeks before planting, compared to seven days for methyl bromide.

Problems with not having methyl bromide

Another problem is restricted use due to labeled safety issues. Telone or 1, 3-D cannot be used in Florida's karst terrains, where it could cause groundwater contamination. The requirement for personal protective equipment when applying 1, 3-D significantly limits worker time in Florida, because of the heat and OSHA requirements. Buffer zone requirements, although reduced by the U.S. Environmental Protection Agency (EPA) from 300 to 100 feet, still restrict the chemical's use. In California, Telone is also limited by township caps and chloropicrin is being reevaluated by the California Department of Pesticide Regulation.

Methyl bromide is a toxic chemical and in a study of 55,000 farm workers exposure to high doses was linked to elevated prostate cancer risk. In an effort to avoid jumping from the frying pan into the fire, the EPA is conducting a soil fumigant cluster risk assessment for methyl bromide, chloropicrin, 1,3-D, metam sodium, dazomet, and iodomethane. The results are due to be published this year.

Another problem potentially slowing the phase-out of methyl bromide is the cost of registering new chemicals. Pesticide companies may not be willing to risk going through the process for a relatively small payback. "Methyl bromide is used on low acreage crops--50,000 acres of tomatoes might seem like a lot, but compared to millions of acres of cotton and corn and soybeans that's a very low acre crop--so there has not been a strong move by pesticide companies to register new pesticides to fill this niche," says Ken Vick, senior national program leader on methyl bromide alternatives at U.S. Department of Agriculture's Agricultural Research Service (USDA-ARS).

Alternatives to methyl bromide

However several promising chemicals are in the registration process or pending registration. Iodomethane, registered by Arysta LifeScience Corporation in Japan for use on timber is waiting registration in the United States. The product evolved out of research by the Methyl Bromide Alternative Urgent Development Program and shows promise for controlling broad spectrum post harvest insects, as well as soil borne diseases, nematodes, weeds, and fungi. One concern though is that since iodine is extremely expensive, the product may turn out to be uneconomical.

Furfural-based Multiguard Protect, distilled from sugarcane with a Generally Recognized as Safe (GRAS) status, works against nematodes and fungal pathogens and is pending registration for greenhouse use. "It's got a lot of things going for it from the standpoint of safety." says Norton. Also pending registration is SEP 100, with active ingredient sodium azide, which controls nematodes, weeds and fungal pathogens and breaks down to ammonia and nitrates, which can be used by plants. Propylene oxide, currently registered only for post harvest uses, also shows potential as a soil applied fumigant. At high rates, propylene oxide could control nutsedge, one of the worst problems Florida tomato growers face. Propylene oxide also controls a broad spectrum of soil borne diseases and nematodes at rates lower than needed for nutsedge control. According to Norton, it leads in terms of harvestable strawberry yields over several years in California's Driscoll strawberry trials.

Despite all the difficulties, methyl bromide use was down by 70 percent of its 1991 amount in 2003 as required by the Montreal Protocol. The reduction was due not only to new materials, but to new methods of delivery and the increasing use of plastic mulches, known as virtually impermeable films (VIP) which keep fumigants in and weeds out.

About one third of strawberry production acreage in California is no longer fumigated with methyl bromide according to the California Strawberry Commission. The most preferred alternative is drip-applied InLine. Also contributing to the trend are strawberry plugs, which are grown in sterile potting media before being transplanted into non-fumigated soil. Currently strawberry plugs are widely planted throughout southern California. "It's definitely taken off," says Frank Sances of the Pacific Ag Group in San Luis Obispo, who developed the technique in California after it was pioneered by researchers at North Carolina State University.

To compare, Europe has six countries with three percent of the European Union strawberry production using soil-less culture.

In developing countries, a mix of non-chemical and chemical alternatives in an integrated pest management approach is successful in replacing methyl bromide in tomato production, reported Mohamed Besri at the Lisbon conference. Besri is a member of the Methyl Bromide Technical Options Committee. The alternative methods used include solarization, steam, grafting, resistant varieties, soil-less culture, biofumigation, and biological control. Denmark, Spain, Holland, and Germany no longer use methyl bromide for tomato production according to Besri.

ARS Researcher Joseph Noling questions whether non-chemical alternatives, even if successful in developing countries, can be transferred to the United States. "I've made this comment repeatedly," says Noling. "Mediterranean desert regimes of the northern coast of Africa, or the Mediterranean area, are just not the same as the U.S." The point is important because critical use exemptions are not allowed if viable economically feasible alternatives to methyl bromide exist.

The right environmental conditions are certainly essential to the success of solarization which works well, killing weed seeds, pathogens, nematodes, and insects, in places where sunlight is guaranteed and the soil can be heated dependably to the necessary temperatures. But Florida is subject to tropical storms and hurricanes. "The very time they would have to be solarizing is the time of maximum storm activity," says Vick. "It's not just that you would get a rain that would cool the surface of the soil, the soil will flood, and when the soil floods your solarization is over."

Other alternative practices such as crop rotation to discourage nematodes, growing resistant varieties, and leaving orchards or vineyards fallow to decrease replant disease, have shown mixed results in U.S. field trials.

Swanton Berry Farm, the first organic strawberry farm in California founded in 1983, uses a combination of crop rotation, predator mites, and a special kind of vacuuming to combat a variety of strawberry pests. "The reality is that those chemicals are quite expensive," says Sandy Brown, vice president of the farm. "So we save all that money and while it does mean increased labor costs we're not spending money on chemical fertilizers and pesticides, and methyl bromide is capital intensive."

The outcome of a lawsuit between the Natural Resources Defense Council (NRDC) and EPA, may decide how much methyl bromide, in the form of exemptions, will be granted to the United States in the future. NRDC is challenging the legality of the first critical use exemptions for 2005. NRDC discovered that at least 10,000 metric tons of methyl bromide--more than the total critical use needs for 2005--have been stockpiled in the United States. The treaty specifically notes that all existing stocks of methyl bromide must be used before new production is permitted.

"How this all turns out, is going to be very important for the growers, for the environment, and for everyone," says ARS'Vick. "And we're hoping for a successful outcome one of these days."
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Author:Hemminger, Pat
Publication:Journal of Soil and Water Conservation
Geographic Code:1USA
Date:Sep 1, 2005
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