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Alternate to traditional soil fumigant ready, study says

Sweet potato growers in California may have an effective alternative to the controversial fumigant methyl bromide, according to a recently completed study from the UC Farm Extension in Merced.

Use of methyl bromide is being phased out under Environmental Protection Agency regulations. Sweet potato farmers in Merced have been able to secure exemptions to continue to use the fumigant in recent years. However, that's expected to quickly come to an end.

Sweet potato farmers use the fumigant to kill weeds in their hotbed nurseries before transferring plants to the field. The chemical is effective -- but regulators have been cracking down on its use because of environmental hazards related to ozone depletion.

After four years of research, Scott Stoddard, vegetable crop specialist at the UC Farm Extension in Merced, has come up with a system he said can effectively replace the use of methyl bromide in hotbed production, and avoid cumbersome permitting and regulatory hurdles.

Using a combination of well-known herbicides -- devrinol and valor -- Stoddard was able, in recent tests, to significantly reduce weeds in hotbed nurseries. The research focused on calculating exact amounts of chemical herbicide to be applied. "So you're taking away something that the EPA doesn't like, and a lot of people don't like, and it's very expensive, and now you've gone to a safe and innocuous herbicide spray that's going to cost you less," he said.

Stoddard said many farmers aren't aware they don't need to use methyl bromide. And the ones aware of his research aren't willing to go "cold turkey," using only herbicide. "Prior to doing this research, people were fumigating, fumigating, fumigating," he said. "Why? People are doing this because their father did it, and their father's father did it."

Bob Weimer, a sweet potato grower in Atwater, recognizes the need for innovation. Not only do sweet potato farmers in California have only one more year to use methyl bromide under current EPA regulations, but the price of the chemical has been steadily increasing. "The cost of methyl bromide is $3,900 acre," he said. "It in itself is forcing growers to move outside the old standards. The real problem is that we lack a lot of alternatives."

It's not as simple as a cultural shift away from fumigants, Weimer said. He's been working with the farm extension on conducting field research, but he said next year he's going to use a fumigant called Vapam (metam sodium) instead of Stoddard's herbicidal recipe.

Herbicides can be effective, but they must be applied precisely or they can damage a farmer's crop, Weimer said. "Application becomes very sensitive because a slight over application creates an issue with the plant production in your beds," he said. "If you underapply, you don't accomplish what you want to accomplish either."

Stoddard recognizes how careful farmers have to be when applying his herbicidal recipe not to damage their crops. However, once embraced, he said, this new technology can save farmers money and improve safety conditions for workers.

Reporter Joshua Emerson Smith can be reached at (209) 385-2486 or