Residual Efficacy of Starch-Encapsulated Microbial Insecticides for Control of Diamondback Moth on Cabbage, 1991

Abstract

Abstract In 2 series of laboratory bioassays, DBM larvae from a laboratory colony (established in 1988 with insects from southwestern Illinois) were confined with cabbage foliage taken from field plots at varying intervals after application of microbial insecticides derived from Bacillus thuringiensis var. kurstaki. Spray solutions were applied to cabbage plots with 3 hollow cone nozzles/row from a 4-row sprayer delivering 30 gal/acre at 50 psi on 18 Jul (first bioassay series) and 1 Aug (second bioassay series). (See Paper 10E for details of the field trial.) All products and experimental formulations contained the same amount of B. thuringiensis. Triton CS-7 adjuvant (6 oz/acre) was included in the Dipel 2 × treatment. Mid-sized DBM larvae were confined in groups of 10 in petri dishes containing 2 leaf disks on moist filter paper. Each treatment was replicated 8 times for total of 80 larvae per treatment per time interval tested. An equal number of larvae confined on foliage from untreated plots served as a control for each bioassay. Mortality of DBM larvae was determined after 3 days' exposure to the leaf disks. In the first bioassay series, DBM larvae were exposed to treated foliage 0, 3, 5, or 7 DAT, while the second bioassay series used foliage 1, 3, 6, or 8 DAT.