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Zapping Sweetpotato Weevils

Irradiation is an effective way to meet quarantine regulations for interstate shipment of sweetpotato roots that can harbor weevils that feed on the roots, an Agricultural Research Service study has shown.

Exposure sterilizes but doesn't kill the weevils, according to entomologist Guy Hallman at the ARS Kika De La Garza Subtropical Agricultural Research Center in Weslaco, Texas. The weevils may remain on the roots until they die a few weeks after being irradiated, but they can't reproduce and they do only negligible damage.

Sweetpotatoes are one of the world's most widely grown crops, with a total harvest of more than 133 million metric tons every year. That translates to about 47 pounds for every person on the planet, with people in the United States consuming four pounds each on average.

But the sweetpotato weevil, Cylas formicarius elegantulus, threatens the popular sweetpotato. It causes serious damage by laying eggs at the base of plants in the field. The larvae that hatch burrow into the roots, causing them to rot. Among food plants, C. formicarius attacks only sweetpotatoes and continues to damage roots after they have been harvested and put in storage.

To prevent the spread of weevils, growers in southern Florida irradiate boniato-type sweetpotatoes that are shipped out of state. The boniato, a white-fleshed sweetpotato, is popular with immigrants to the United States from the Caribbean and other areas and also represents a valuable export.

In 2000, the first year the technique was used to treat boniatos, 193 tons were irradiated and shipped. By 2001, the total had grown to 208 tons. The technique has been approved by the U.S. Department of Agriculture's Animal and Plant Health Inspection Service for use in Florida and Hawaii.

Read more about this research in the April issue of Agricultural Research magazine.

ARS is USDA's chief scientific research agency.