But during the trial, the plaintiffs' attorneys unearthed a memo from a DuPont salesman showing that the company had known about gummy stem blight's resistance to Benlate since 1994. Scott is representing four more Rio Grande Valley produce companies in lawsuits against DuPont scheduled to go to trial in December. Pesticide use in the United States increased tenfold from 1945 through 1989. During the same period, the number of insect pests resistant to pesticides increased, and crop losses nearly doubled, from 7 to 13 percent, according to a report issued last year by the Pesticide Action Network. Resistance forms when selection pressure is put on an organism and it changes in response, explains Lynn Brandenberger, a horticulturist with the Texas agricultural extension service.
Overuse leads to resistance developing more quickly.
At Starr Produce Company's 15,000-acre farm, spraying in 1997 began even before the first symptoms appeared and continued through the harvest. Or what would have been the harvest. More than 90 percent of the samples were highly resistant. Sometimes you just up the dose and that helps for a little while. Farmers had to stop growing potatoes in several major production areas.