It’s said that “timing is everything,” and that’s apparently true for cotton growers trying to control beet armyworms. Tests by an Agricultural Research Service scientist have shown that applying pesticides to cotton after sunrise reduces beet armyworm populations by 96 percent.

The finding is significant because the beet armyworm costs U.S. cotton growers tens of millions of dollars in crop losses and pesticide expenses each year. In 1995, the Lower Rio Grande Valley in Texas was especially hard hit. The ARS studies were done at the agency’s Western Cotton Research Laboratory, Phoenix, Ariz.

Beet armyworm larvae generally prefer cotton leaves, but as pest numbers rise, older larvae tend to enter the plant’s flowers. Traditional pre-dawn pesticide applications only kill about 12 percent of the beet armyworms in flowers because the flowers are still closed, shielding the pests. After sunrise, the flowers open, leaving the pests vulnerable to chemical control.

To take advantage of the finding, cotton growers will have to do more than simply spray a few hours later. Growers typically apply chemicals before sunrise when winds are lighter to reduce pesticide drift. Also, bees, which are critical for pollination, are still safely inside their hives at that hour. This means growers must carefully coordinate after-sunrise pesticide applications with beekeepers to ensure that hives are temporarily moved to safer locations.

Scientific contact: David H. Akey, ARS Western Cotton Research Laboratory, Phoenix, Ariz., phone (602) 379-3524, fax (602) 379-4509, thenneb@asrr.arsusda.gov.