Evaluation of Treatment Thresholds for Control of Bollworms and Tobacco Budworms in Transgenic Bt Cotton in South Carolina

John A. DuRant


A field study was conducted to compare the transgenic cotton line, 'MON 1076', expressing the delta-endotoxin from the bacterium, Bacillus thuringiensis subsp. kurstaki (Berliner) (Bt) with the nontransgenic cultivar, 'Coker 312' (non-Bt), for tolerance to injury by the bollworm, Helicoverpa zea (Boddie), and the tobacco budworm, Heliothis virescens (F.). Insecticide treatment regimens for the Bt cotton were 2%, 5%, and 8% damage to squares, 'as needed' based on 5% damage to squares in the non-Bt cotton, and 'untreated'. These treatments were compared with non-Bt cotton treated 'as needed' and 'untreated'. Damage to squares remained below treatment thresholds for the Bt cotton with one exception, when the 2% threshold treatment received one insecticide application. The non-Bt ('as needed') and Bt ('as needed') treatments each received five insecticide applications. Damage to squares was significantly lower for all Bt cotton treatments than for the non-Bt cotton treatments. Lint percentage was significantly higher for the non-Bt cotton than for the Bt cotton treatments and the lint yield for the non-Bt ('as needed') cotton was significantly higher than for the Bt ('as needed') cotton. Multiple applications of insecticides to the Bt cotton did not increase yield compared with Bt cotton which received no insecticide applications. 'MON 1076' exhibited a high degree of resistance to injury by the bollworm/ tobacco budworm complex, although the yield potential of this line appeared lower than that of the nontransgenic cultivar, 'Coker 312'.

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pp. 1073 - 1075
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998