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National Programs
Methyl Bromide Alternatives
National Program Annual Report:
Introduction
The fumigant, methyl bromide, has been the cornerstone for production and storage of a wide range of commodities for over 50 years. In 1992 the Montreal Protocol identified methyl bromide as an ozone depletor and took steps to ban its production and importation in developed countries, worldwide. In 1993, the United States Environmental Protection Agency (EPA) pursuant to provisions of the U.S. Clean Air Act promulgated a regulation to ban production and importation of methyl bromide in the U.S. on January 1, 2001. Language in the fiscal year 1999 budget extended the phaseout date in the U.S. to January 1, 2005, to be consistent with the phaseout date set by the Montreal Protocol for other developed countries. This program, consisting of postharvest commodity and preplant soil fumigation components, houses the agency’s research program to develop practical, effective, environmentally acceptable alternatives to methyl bromide.
Workshops were held in Orlando, Florida, December 10, 1998, and Monterey, California, April 20-21, 1999, that involved ARS, university and private sector scientists, environmental officials, state agricultural officials, and a diverse group of growers and other methyl bromide users. Input from stakeholders on problems and research needs provided information needed for ARS to properly focus this research program on the most critical client problems.
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Selected Accomplishments for Fiscal Year 1998 (listed by Component)
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Preplant Soil Fumigation Alternatives
Approximately 75 percent of the methyl bromide used in the United States is used to fumigate soil before planting crops to kill weeds, plant pathogens, nematodes, and insects. There is currently no registered fumigant which can directly replace methyl bromide for all uses. An array of alternative control measures will be required. Such measures include combinations of fungicides, herbicides, and insecticides; replacement fumigants; and non chemical alternatives, such as cultural changes in cropping systems, development of resistant crops, biological control, and integrated pest management to prevent a buildup of nematodes, weeds, and insect pests. |
| Combination of fungus and bacterium promising for control of tomato disease. With the phaseout of methyl bromide approaching, farmers need another way to control the serious fungal disease, Fusarium wilt, on vegetables, melons and other crops. By combining the fungus Gliocladium virens, and bacteria, Burkholderia vietnamiensis, researchers were able to achieve higher levels of disease control than with either agent alone in several field locations. Combined with other strategies, this biological control approach may be of help in an overall strategy for replacing methyl bromide for several crops.
Nonpathogenic fungal variants offer protection against diseases. Soilborne diseases now controlled by soil fumigation with methyl bromide are expected to pose serious problems for farmers after the methyl bromide phaseout. One approach to disease control, called biological control, is treatment with microbes that are antagonistic to pathogens. Scientists have discovered that treatment with a nonpathogenic strain of the Fusarium fungus can significantly reduce disease losses on several crops. Growers have expressed interest in further testing of this approach, and more field and greenhouse trials are under way.
New irradiation quarantine treatment to allow shipment of fruit from Hawaii. Irradiation treatments have been determined for the effective treatment of koa seedworm/litchi fruit moth, important pests of a range of Hawaii-grown fruit, and the yellow flower thrips on tropical fruits. Results also show that papaya, rambutan, carambola, lychee, and mango can tolerate gamma-radiation up to 0.9kGy, suggesting that irradiation to eliminate fruit flies is a feasible and efficacious quarantine treatment for tropical fruits and other fresh produce.
Soil solarization can be useful to reduce diseases and weeds in vegetable production. Researchers have found that plastic laid over fields traps heat from the sun and can result in soil temperatures that kill pathogens and weeds. This technique may be useful as part of methyl bromide alternative schemes in suitable climates (lots of sunlight) and with cropping systems that allow enough time for treatment (several weeks). Large-scale field tests to demonstrate the usefulness of this technique are being conducted at several locations in Florida.
Application of alternative fumigants through drip irrigation systems shows promise as an alternative to methyl bromide. Applying 1-3 dichloropropene and chloropicrin through drip irrigation systems in tarped beds before planting has been shown to be an effective method for controlling diseases and weeds in California strawberry fields. Compared to methyl bromide, this alternative fumigation method resulted in about 90 percent of the yield during large-scale testing in several locations. This procedure can usually be incorporated into current cropping practices and may be an economical alternative to methyl bromide.
Biological control of nutsedge. Yellow and purple nutsedges are the most damaging weeds in vegetable production in Florida and also among the hardest to control. Soil fumigation with methyl bromide works, but it is being phased out and growers do not have an acceptable alternative. A fungal pathogen has been identified that appears to be effective against nutsedges. The optimal growth conditions for production of this agent have been established and its effectiveness in large-scale plots is being tested.
New films reduce methyl bromide emissions. Most of the methyl bromide applied in typical fumigations with polyethylene plastic tarps escapes to the atmosphere and poses an environmental risk because of damage to the ozone layer. Using virtually impermeable films and 50 to 75 percent less methyl bromide, researchers have shown the emissions can be cut from about
60 percent to less than 5 percent with little loss in pathogen and weed control. These findings may be of benefit as the amount of methyl bromide available for soil fumigation is stepped down in 2001 and 2003.
Plant extracts effective against plant pathogens. Soilborne plant pathogens cause significant disease losses on many crops. Soil fumigation with methyl bromide is effective in controlling such diseases, but its use will be phased out by 2005. Researchers recently found that natural plant products, primarily essential oils, were effective against such diseases. Their utility for commercial production is being evaluated, and they may offer alternatives to methyl bromide for some crops.
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Postharvest Commodity Treatment (Including Structural)
About 12 to 15 percent of the methyl bromide used in the United States is used to disinfest harvested commodities of insects and other arthropod pests. About 10 percent of this (1 to 2 percent of total use) is used as quarantine treatments. In 1994, the last year for which accurate data are available, $431 million of U.S. commodities were treated with methyl bromide as a condition of entry of the importing country to prevent inadvertent introduction of new species of insects into their country from the U.S. These commodities included apples and cherries to Japan, cotton and peaches to Mexico, oak logs to Europe, and strawberries to Australia. Methyl bromide is also used extensively at U.S. ports of entry to disinfest commodities that are found on inspection to be infested with exotic pests, the introduction of which would cause irreparable harm to U.S. agriculture. Methyl bromide is currently the only emergency fumigant available to disinfest commodities from growing areas quarantined as a result of the invasion of exotic pests, such as the Mediterranean fruit fly. The other 90 percent of methyl bromide used for postharvest commodity fumigation is used to control non-quarantine insects and other arthropods on a wide range of commodities to maintain quality during storage and processing. |
| New quarantine treatment for mealybugs. The U.S. has recently been invaded by several devastating pests of agriculture. Several more pests, including the pink mealybug, threaten to come into the U.S. from nearby infested areas. A new hot-water quarantine treatment was developed for mealybugs on imported limes to allow importation of limes and other commodities
from areas, such as the Bahamas, into the U.S. without the risk of accidentally importing quarantined pests. The availability of approved, effective quarantine treatments removes the motivation to smuggle untreated (and risky) fruit into the U.S.
Rapid increase in heat may be more effective than gradual increase for quarantine heat treatments. For some commodities, heat treatments are a practical alternative to methyl bromide fumigation to rid the commodity of quarantine pests that might be inadvertently spread with the commodity to areas where the pest does not occur. This research shows for the first time that the rate that the commodity is heated is important with respect to the efficacy of the treatment. This finding indicates that heating rate must be considered by quarantine regulatory agencies when certifying heat quarantine treatments to disinfest commodities.
Methyl iodide and sulfuryl fluoride potential methyl bromide replacements for commodity fumigations. Toxicity studies of methyl iodide and sulfuryl fluoride established that these two fumigants have great potential for replacing methyl bromide treatments. Methyl iodide was toxic to all species and life stages at doses equal to or less that those for methyl bromide, and it was toxic in short exposure periods. Sulfuryl fluoride was not very toxic to the egg stage of some common lepidopterous pests but still had the potential to be a methyl bromide replacement in situations, such as walnuts, where egg stage does not normally occur at time of harvest.
Methyl bromide recapture unit for postharvest commodity fumigation. A portable pilot methyl bromide adsorption unit was built and tested at fumigation facilities in California, Virginia, and North Carolina. In all cases, effective adsorption of residual methyl bromide was achieved. Although quarantine uses of methyl bromide are currently not scheduled for phaseout, continued use for this purpose may eventually depend on availability of recapture technology to prevent release of methyl bromide to the atmosphere during and after the fumigation process.
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