In 1995, ten fields (25 to 40 a) of irrigated cotton on the same farm located north of Mercedes, Hidalgo County, Texas were sampled full season. Fields were adjoining or within 0.5 mi.. of each other and under the same production system. Yield potential was 1000 lbs. lint/acre. The lepidopteran pests attacking these fields included beet armyworm, cabbage looper, cotton bollworm and tobacco budworm. This was the only year that a spring boll weevil eradication program was conducted in the Lower Rio Grande Valley. Irrigated cotton comprised 225,000 acres of the total 360,000 acres planted in 1995. A fifty-two day drought was broken with 4.88 inches of rainfall on May 30 and 31. Temperatures were higher than normal during most of May, June and all of July.

These ten fields each received seven applications of malathion ulv as part of the Boll Weevil Eradication Program. These fields were also part of a malathion rate test of 16 oz. (5 fields) versus 12 oz. (5 fields) per acre. Weekly counts were made of healthy and insect damaged fruit in each field. Lepidopteran larval damage was excessive. It was responsible for a range of 0 to 49% of the estimated total yield loss by field. This variation of larval damage by field is as expected for insect pest population distributions. None of the fields, however, escaped high yield losses which are consistent and characteristic to climatic factors.