By Brad Haire
University of Georgia

Scientists in Georgia are developing a system that uses plants
like mustard, collards and turnips to replace a soon-to-be-
banned farm fumigant.

Methyl bromide is an efficient, reliable fumigant used worldwide
to kill bugs, weeds and other pests. For the past half-century,
it’s been used primarily as a soil fumigant for many farm
crops.

Critical

It’s “the best game in town” for vegetable growers, said Ken
Seebold, a plant pathologist with the University of Georgia
College of Agricultural and Environmental Sciences. They use it
to quickly sterilize their soil beds before planting.

“The growers in one step can use it to control most of the soil
plant pathogens, nematodes and weeds,” he said. “This gives
their young transplants a critical head start.”

But an international monitoring group has slated methyl bromide
to be completely phased out of production and use by Dec. 31,
2004.

Vegetable farmers are concerned. They have no viable
alternative, Seebold said, to do what methyl bromide does so
effectively for them. The growers recently got a critical-use
exemption to use methyl bromide through 2005. But that’s only a
temporary reprieve.

Natural fumigant

Seebold and a team of CAES scientists are trying to develop a
management strategy that will use a natural fumigant found in
brassica crops — collards and their cousins. They’re working on
a $422,000 grant from the U.S. Department of Agriculture.

Brassica crops contain compounds called glucosinolates. When
these compounds break down in soil, Seebold said, they release
isothiocyanates, which can kill soil pests in much the same way
methyl bromide does.

This natural fumigation quality of the brassica family has been
known for years, Seebold said. But no viable way has been
developed to use it economically on a vegetable farm.

Over the next three years, Seebold and his team will grow local
and exotic brassica crops and monitor the fumigation potential
of each. Because brassicas are generally lower-value crops,
farmers don’t fumigate beds before planting them.

The scientists will work out a system that might allow a farmer
to grow these crops specifically to till back into the ground to
break down and fumigate the soil in preparation for higher-value
crops like tomatoes, cucumbers or squash.

The farmer could harvest part of his brassica crop for market
and till in the rest to use as a fumigant, he said.

“The most important thing for any alternative to methyl bromide
is to be economically viable for the farmer,” he said.

Protocol

The Montreal Protocol is an international treaty to control the
production and trade of ozone-depleting substances. More than
160 countries signed it, including the United States.

In 1992, its regulating board found that methyl bromide depleted
the ozone layer and would have to be phased out of production
and use. Barring any further critical-use exemptions, methyl
bromide is slated to be completely banned by 2005.

The United States uses about 21,000 tons of methyl bromide
annually. Agriculture uses the lion’s share of this.

The U.S. Animal and Plant Health Inspection Service also uses it
to fumigate foreign commodity shipments for invasive species. A
small amount is used to fumigate buildings.