This research was conducted in 1984 and 1985 to determine the effects of mepiquat chloride (PIX^®) on natural plant resistance to the tobacco budworm, Heliothis virescens F., in cotton, Gossypium hirsutum L. The experimental design was a two-way whole split plot randomized complete block. 'Stoneville 213' was planted in all plots. Whole plots were: (1) three levels of PIX with TBW and (2) three levels of PIX without TBW. On plots that received TBW, first instar larvae were applied twice a week for four weeks beginning the first week after the first application of PIX (+TBW). Plots without TBW were treated weekly with azinphosmethyl plus fenvalerate to control insects (-TBW). Insects were controlled in all test plots from the beginning of the season until one week before the first treatment was applied. Also, beginning one week following the last treatment, insects were controlled in all test plots for the remainder of the season. The split plots were three levels of PIX, 0, 1 and 2. Level 0 was no PIX, level 1 was 50g a.i./ha and level 2 was 100g a.i./ha. Level 2 was a split application of 50g a.i./ha one day and 50g a.i./ha 14 days later. These applications were applied at the recommended time of 5-6 blooms/20m of row or when the plant reached 60 cm in height.

Twenty-five boll samples were analyzed to determine lint percent, boll size and seed index. Cotton was harvested twice to determine earliness. In the -TBW plots there were no significant differences in total yield; however at first harvest, PIX at level 1 and 2 resulted in more cotton than the zero level for both years. In the +TBW plots, there were no significant increases or decreases in yield either year. In the -TBW plots PIX at levels I and 2 reduced lint percent and increased seed index. Based on these results, there is no indication of increased natural plant resistance to the tobacco budworm due to the application of PIX.