In 1977 synthetic pyrethrin insecticides were first marketed in the United States for cotton insect control. Their effectiveness in controlling tobacco budworms, Heliothis virescens (Fabricius), and cotton bollworms, Heliothis zea (Boddie), contributed to increased cotton yields.

In 1981, Shell Development Company conducted a series of trials in which several rates of PYDRIN^® Insecticide were compared for cotton insect control. Fixed-wing aircraft were used for conventional applications with water and for ultra low volume applications with non-volatile vegetable oils (usually cottonseed oil) as carriers. From these trials, it was determined that 0.20 lb ai/acre of PYDRIN applied to cotton in either water or vegetable oil consistently gave higher yields than rates of 0.10 lb ai/acre or less (Table 1). Insect control was somewhat better using 0.20 lb ai/acre, however, not all the increased yield was attributed to insect control (Sckerl 1981). Yield increases in cotton resulting from undetermined factors have been experienced previously following the use of fenvalerate (Highwood 1979).

Based on the results from the 1981 field program, an experiment was designed to determine whether the observed increased yield was attributed to superior insect control or some plant physiological phenomenon.