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USDA Seeks Alternatives to Methyl Bromide for Quarantine Security

By Doris Stanley
February 20, 1997

Every day, goods from around the world flow to the United States’ borders. Like other countries, the United States tries to protect the nation’s crops from pests that might hitch a ride into this country on the incoming goods. As part of the protection effort, the U.S. Department of Agriculture inspects all incoming plants, plant products and other regulated articles.

Since World War II, USDA has required that commodity treatments for quarantine pests, especially fruit flies, meet or exceed a statistical standard called Probit 9. This standard says treatments must kill or sterilize 99.9968 percent of the pests in a test of at least 100,000 individual pests.

Treatments with heat, cold and irradiation have been used, but fumigation with methyl bromide has been the most practical option for many commodities. The more basic problem now: Methyl bromide has been identified as an ozone depletor and is scheduled to be banned in 2001.

Scientists with USDA’s Agricultural Research Service are working with the department’s Animal and Plant Health Inspection Service to come up with a less rigorous standard than Probit 9 that might be more appropriate for certain low-risk commodities.

Probit 9 was adopted as a one-size-fits-all standard to provide adequate quarantine security for the highest-risk commodities. While this standard has a long history of usefulness, it may now be overly severe for commodities that are rarely or minimally infested and that have a very low probability of carrying exotic pests.

USDA scientists suggest that the severity of the treatment be tailored to the level of risk posed by the commodity. This would allow expanded use of controlled atmospheres and other treatments that previously have not met Probit 9 requirements. Risk might be based on rate of pest infestation, pest survival and reproductive capacity and the effects of harvest, processing and distribution on the pest’s ability to survive and establish itself. Although packaging, shipping conditions or season of shipment aren’t considered in commodity quarantine under Probit 9, they’re important in determining the risk a particular commodity presents to the importing country.

Other approaches being considered in lieu of methyl bromide are discussed in the January 1997 issue of Methyl Bromide Alternatives newsletter. The newsletter can be accessed on the World Wide Web at:


Scientific contact: Kenneth W. Vick, USDA-ARS National Program Staff, Beltsville, Md., phone (301) 504-5321