This work deals quantitatively with the generation, dispersion, and deposition of pesticide droplets on vegetation and with off-target drift of undeposited droplets. A computer simulation model for calculating dispersion, deposition, and drift is described, with comparisons between calculated results and field measurement results. The model includes the effects of aircraft vortex, atmospheric turbulence, droplet evaporation, and droplet deposition on foliage. Model output includes values of droplet deposit density and size on foliage and ground as well as droplet concentration and size in the drift cloud. In addition, a detailed description of droplet atomizer characterization methods is presented along with a large number of atomizer spectrum results for atomizers in current use. An analysis of a number of forestry spraying innovations is presented. This text should be a useful tool in assessing the efficacy and environmental impact of proposed and actual forest spray operations.

Introduced to the technical aspects of forestry aerial spraying in the mid-1970's, we were immediately impressed by the complexity of the process of delivering pesticide to foliage. At that time, there was a vigorous public debate in New Brunswick about the ecological and public h~alth impacts of the annual spray program for the control of defoliation of spruce and fir trees by the spruce budworm. The forest industry is important to the province and changes to the established procedures of budworm control could have major economic implications. A rational debate required reliable information about the mechanics of the spraying process. There was a need to supply missing information as to required pesticide application rates, atomizer performance, off-target drift and deposit, and the effects of weather and aircraft operating factors. We were invited to initiate a research program in this domain by New Brunswick forest management officials, and what follows in this book is a logical and quantitative description of the overall process based on our own research and that of others over the intervening years. After a short introduction to aerial spraying, we begin (Chapter 2) by describing forest stands in terms of their interaction with suspended atmospheric particulate material carried along by the wind and susceptible to deposition on foliage. We introduce foliage simulators and their use in measuring the deposit of sprayed pesticide on foliage, the "biological interface" between pest and pesticide.