Insect Control on Flue-Cured Tobacco with Bacillus Thuringiensis var. Kurstaki Spray Formulations, 1982

Abstract

Abstract Two wettable powder and 3 aqueous formulations of Bacillus thuringiensis (B.t.) var. kurstaki were tested against artificial infestations of tobacco budworms and tobacco hornworms, and natural Infestations of tobacco budworms and tomato hornworms on flue-cured tobacco in 3 separate tests at Oxford, NC. Some of the treatments also contained 1 of 2 polyvinyl acetate stickers (Rhoplex B60A and Polyco 2142), which were evaluated for increasing B.t. efficacy. ‘Speight G-70’ was used in Tests 1 and 2, while NC 2326 was used in the final test. All tobacco was transplanted onTlay 7 into a field of Vance sandy loam soil which had been treated on Apr 19 with Telone C-17 (98.2 1/ha), Paarlan (2.3 1/ha), and Ridomil (2.3 1/ha). Plants were placed on 55.9-cm centers with 1.2 m between rows. Plants in Test 1 were infested with 1 laboratory-reared tobacco budworm per plant on Jun 15. Larvae were ca 2 days old and were from a colony that had been started from field collections and cultured for ca 10 generations on artificial diet. On Jun 17 plants were examined for successful budworm establishments and 40 plots of 15 infested plants each were marked in a randomized complete block design with 5 blocks and 8 treatments. The following 2 days there was a very heavy rainfall (4.1 cm) that prevented spraying for several days. Plots were treated on Jun 21 with CO2-powered backpack sprayer with an adjustable nozzle at a rate of 233.8 1/ha with 4.2 kg/cm. Plants were examined for insects 3 and 7 days after spraying, and on day 7 they were subjectively rated from 0-7 for tobacco budworm damage. Temperatures were mild (max. 31.1°C) and there was little rainfall (0.1 cm) after spraying. After the final plant examination in Test 1, the plants in all plots were cut off near the ground. One sucker was allowed to grow per plant and this regrowth was used in Test 2. For this test, plants were infested with one 2 day old tobacco budworms on Jul 27, and on Jul 30, 40 plots of 15 plants each were marked off in a randomized complete block design. Treatments were applied as in Test 1 on Aug 2 and plants were checked 3 and 7 days later. Once again the weather was rainy (1.8 cm) after infestation, but no rain was recorded after spraying, when temperatures reached 32°C for 4 days. For Test 3, tobacco regrowth on NC 2326 was infested with 2 second instar tobacco hornworms per plant on Aug 9. These insects were from an artificial diet fed laboratory colony maintained at Oxford. This test was set up in a randomized complete block design with 5 blocks and 7 treatments. The plots were sprayed on Aug 10, and examined 3 and 7 days later. The weather was wet both before and after spraying in this test (7.4 cm rain)