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Measurement of foliar deposits of Bt and their relation to efficacy

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Fast, P. G.; Kettela, E. G.; Wiesner, C.

Year Published

1985

Publication

In: Grimble, David G.; Lewis, Franklin B., coords. Proceedings, Symposium: Microbial control of spruce budworms and gypsy moths; 1984 April 10-12; Windsor Locks, CT. Gen. Tech. Rep. NE-100. Broomall, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 148-149

Abstract

Interest in and discussion of the relationship between droplet spectrum emitted and droplet spectrum deposited, spray cloud behaviour, the relationship between droplets deposited and efficacy, and optimum droplet size, has increased in recent years and has resulted in a number of collaborative studies addressing aspects of these questions. The questions are particularly pertinent to operational use of Bacillus thuringiensis (Bt) preparations because Bt must be ingested, probably repeatedly, (Fast and Reginiere, Can. Ent. 116: 123-130; 1984) before it can act. Therefore, numbers of droplets deposited, their distribution on foliage, the probability of a larva encountering them, and the dose in a given droplet are important to efficacy. These considerations are as equally important to optimization of applications of contact insecticides, but they do not seem to have been adequately explored. The studies of spray cloud behaviour and deposition by the New Brunswick Spray Efficacy Research Group have established the optimum droplet size for deposition on coniferous foliage, as well as many of the parameters governing spray deposition. Fast and A. Sundaram, have begun the exploration of the effects of drop size, drop density (drops/ needle or /cm. sq.) and Bt concentration on the efficacy of Bt in laboratory bioassays on foliage. Here we present a narrative summary of the results of a field trial designed to measure the relationship of the number and spectrum of droplets deposited on balsam and spruce foliage in field applications to the emitted droplet spectrum and to the efficacy of Bt. Space limits this discussion to a broad brush description of the experiment and the conclusions reached. A detailed description is in preparation. The experiment was jointly funded by Canadian Forestry Service, Forest Protection Limited, and USDA-Forest Service (CANUSA) .

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Citation

Fast, P. G.; Kettela, E. G.; Wiesner, C. 1985. Measurement of foliar deposits of Bt and their relation to efficacy. In: Grimble, David G.; Lewis, Franklin B., coords. Proceedings, Symposium: Microbial control of spruce budworms and gypsy moths; 1984 April 10-12; Windsor Locks, CT. Gen. Tech. Rep. NE-100. Broomall, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 148-149

Last updated on: June 23, 2007