Effect of treatment regimen on control of Heliothis virescens and Helicoverpa zea (Lepidoptera: Noctuidae) on cotton
Durant, J.A.
Four foliar insecticide treatments [AI]/ha), cypermethrin (0.067 kg), Bacillus thuringiensis subsp. kurstaki (Berliner) (29.6 billion International Units [BIU]), amitraz (0.14 kg), and B. thuringiensis + amitraz (29.6 BIU + 0.14 kg), were evaluated for influence on economic returns and for efficacy against the tobacco budworm-bollworm complex, Heliothis virescens (F.) and Helicoverpa zea (Boddie), on cotton, Gossypium hirsutum L., at Florence, S.C., in 1988 and 1989. Each treatment was applied at regimens of scheduled applications (every 2-7 d, season-long), a threshold of five eggs per 100 plants, and a threshold of six larvae per 100 plants. Both years were characterized by low tobacco budworm-bollworm population densities during June and early July followed by sharp increases in mid-July. Cotton fleahopper, Pseudatomoscelis seriatus (Reuter), densities did not exceed 1 per 10 plants. Cypermethrin and B. thuringiensis were the most effective and least effective treatments, respectively. Differences among treatment regimens for each insecticide usually were nonsignificant, but the efficacy of B. thuringiensis + amitraz was significantly reduced in 1988 when treatments were delayed until the larval threshold was reached. Economic returns were greater for the egg and larval thresholds than for the scheduled regimen. The low population densities of H. virescens, H. zea, and cotton fleahoppers before mid-July had no apparent effect on yields, and 15-17 season-long scheduled insecticide applications beginning in mid-June offered no advantage compared with five to eight applications (larval threshold) beginning in July.
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