ABERDEEN, Idaho--An insecticide previously approved only for field corn and non-crop uses is headed for release next spring in potatoes, thanks to an integrated pest management project for wireworm control led by University of Idaho entomologist Juan Manuel Alvarez.
The insecticide, fipronil, received U.S. Environmental Protection Agency approval for use in potatoes this month (September). While all other insecticides currently used against wireworms are organophosphates and carbamates-older classes of chemicals being scrutinized by the EPA-fipronil is in a newer class of chemicals called phenylpyrazoles.
After four years of side-by-side comparisons at the University of Idaho's Kimberly Research and Extension Center, Alvarez says fipronil performed more effectively and consistently against wireworms than any other chemicals evaluated. Not only did it hold wireworm damage to the lowest percentage of affected tubers and the lowest number of holes per tuber, it did so without reducing the potatoes' highly valued size.
"We're excited about it," says Keith Esplin, executive director of the Potato Growers of Idaho. "Although not perfect, it's a better control and we're hoping it helps growers raise a larger percentage of
U.S. No. 1s-which will mean more money in their pockets."
Control options are critical when it comes to battling these crop-threatening larvae of the click beetle. Although click beetle adults are innocuous to crops, their slender, hard-bodied larvae feed on seed pieces and tunnel into tubers, affecting up to a third of the potatoes in individual Idaho fields, Alvarez says. After harvest, damaged tubers that look like they've been studded with nail holes are downgraded or downright rejected, and the processing industry has zero tolerance for the presence of wireworms themselves in the raw product.
Wireworms have proved especially difficult to control because their life cycle extends as long as six years and because they spend much of it below the reach of the preventative chemicals that growers routinely apply to soils at planting. Alvarez says wireworms won't move toward soil surfaces until soil temperatures reach 50 degrees Fahrenheit in spring, and they return to cooler, lower soil levels during the dog days of summer. He and his research partners have documented that most wireworm damage in Idaho potatoes occurs after mid-June and that the insects' activity actually peaks in mid- and late September. The longer tubers remain in the ground, the higher the percentage of wireworm injury.