The sweetpotato whitefly (Bemisia tabaci Gen.) has been a serious pest of cotton (Gossypium spp.) in the Imperial Valley of California since 1981. During the autumn of 1990 a new species of whitefly (silverleaf whitefly) became established on vegetable crops and overwintered in greater numbers than sweetpotato whitefly had in previous years. Silverleaf whitefly infested spring vegetables in 1991. The silverleaf whitefly became established in 1991 cotton plantings causing much more severe damage than sweetpotato whitefly had in years past. Cotton plants were defoliated by silverleaf whitefly during late July and August, greatly reducing yields. Whitefly population again overwintered on vegetable crops in 1991 to infest the 1992 cotton crop following a population increase on spring vegetables. Several insecticides or combinations of insecticides provided sufficient control of whitefly populations to prevent premature defoliation of cotton plants producing yields three to four times greater than the control. Some of the insecticides which were efficacious against the silverleaf whitefly are not currently registered for use in the United States or California. Other insecticides registered for use will not be cost effective at rates used considering the number of applications needed to control the silverleaf whitefly during the cotton production season.