Methyl bromide, a chemical commonly used by vegetable farmers to control pests, is being phased out of use in the United States. University of Georgia experts have developed an alternative method farmers could use.
The United Nations Environmental Program began the phase-out of methyl bromide in 1992. The program was authorized by the Montreal Protocol, a treaty signed by the United States and more than 180 other countries to control ozone-depleting substances.
The phase-out was to be completed by Jan. 1, 2005. Existing stockpiles could be used, but the United States wasn't allowed to import or produce methyl bromide after that.
“Nobody knows how long the current stockpiles will last,” says Terry Kelley, a vegetable horticulturist with the UGA Cooperative Extension. “But speculation is that they will be exhausted in 2008.”
For years, farmers have planted some vegetables in planting beds covered in plastic, which helps them consistently control the growing environment for high-valued vegetable crops like tomatoes, eggplants, squash, strawberries and peppers. Methyl bromide has been an effective, economical way to sterilize these beds against diseases and problem weeds prior to planting, Kelley says.
“No one single fumigant could do what methyl bromide could do for vegetable growers,” Kelley says.
Scientists with the UGA College of Agricultural and Environmental Sciences knew this was the biggest problem facing the vegetable industry. They have been trying to find alternatives.
One alternative method that shows promise uses a combination of three chemicals,
Telone II, chloropicrin and Metam, says David Langston, a CAES plant pathologist.
All three chemicals are labeled for use on vegetables.
Langston and Stanley Culpepper, a CAES weed scientist, began looking at this “three-way” system in 1999. Research literature from the 1980s shows it could work. But it needed tweaking.
“What we have done is refine the system,” Langston says.
For the three-way system to work, a farmer needs to know how to apply the chemicals in order to deliver each chemical to a specific depth and location in the bed. The soil needs to be moist, too, but not too moist.
To cover beds, farmers use several different farm implements on different tractors.
The CAES scientists have developed new tractor implements to help farmers safely and accurately deliver each chemical in the three-way system without adding additional trips over a field.
The price of methyl bromide has tripled in the past decade. It currently costs vegetable farmers about $450 per acre to use. The chemicals for the three-way system cost about $360 per acre.
But with one use of methyl bromide, farmers can often plant two to three consecutive vegetable crops before reworking the plastic beds.
It is unclear how many crops one three-way treatment will be able to consistently cover, Langston says.
Langston and Culpepper are testing the three-way system on three farms in south Georgia this spring. They are also testing different plastic types to see which works best with the system.
The CAES experts are producing an educational DVD to train Georgia's vegetable industry and farmers who want to try the three-way methyl bromide alternative.
Because no alternative for methyl bromide has been found, the United States and other countries have received “critical-use exemptions,” says Kelley, who has helped the Georgia Fruit and Vegetable Growers Association compile and prepare the critical-use exemption application. This allows limited importation and production of methyl bromide for use in the United States.
In 2005, the United States was allowed to import or produce about 17 million pounds of methyl bromide, about 30 percent of what was allowed in 1991. The U.S. exemption this year allows for 15 million pounds.