Control of Tobacco Budworms and Tobacco Hornworms with Bacillus Thuringiensis Var. Kurstaki, 1982

Tobacco was transplanted into plots 80 ft long and 4-rows wide (15 ft) in a Norfolk loamy sand soil on 29 Apr. at the Central Crops Res. Stn. Clayton, N.C. Plots were arranged in a randomized complete-block design with three replicates. On 10 June, fifteen 2-day old Heliothis virescens larvae, from a laboratory culture, were placed in the buds of 15 uniform sized plants in the two left-most rows in each plot. On 11 June, treatments were applied to these two rows usiing a John Deere Hi-Cycle 600 boom sprayer fitted with single D2-33 FC nozzle per row. Sprays were applied at 60 lb/in2 at 1.4 mph to deliver 25 gal of finished spray per acre. At 3 and 10 days after application, the plants that had received budworms were examined and all larvae counted. Fourteen days posttreatment a defoliation count was made on the same plants. Approximately 1 month posttreatment, all plants in the 2 border rows were cut to leave 3 to 4 leaf nodes. Suckers grew from these leaf nodes and after ca. 2 weeks, all but one healthy sucker per plant were removed. On 15 July, 15 uniform sized suckers per row in each plot were infested with budworms as previously described. On 20 July, these rows were treated as described above and the two left-most rows acted as a buffer. Surviving budworms were counted 3, 6, and 10 days posttreatment while a leaf damage count (measured in 1/10 leaf equivalent per plant and summed over all 30 plants) was made after 14 days. A natural infestation of tobacco hornworms was also present and evaluated 3 and 10 days posttreatment from 10 random plants per row (20 per plot). Hornworm defoliation was estimated 21 days posttreatment. Data were transformed to the square root of count + 0.5 before analysis of variance.