In this paper we report the results of a series of laboratory experiments that were designed to quantify the effects of adding an anti-evaporant to a permethrin formulation. Assessments were made of the effects of the anti-evaporant upon: droplet evaporation rates, droplet retention and bounce, droplet spread, and the implications of these parameters for an improved biological efficacy.
Evaporation rates were assessed using a 2m high, temperature controlled, droplet settling tower. A monosize droplet generator was used to produce the droplets which were measured at their entry and exit from the tower using water sensitive papers. The difference in droplet size was then used to calculate the mean droplet evaporation rate for each of the temperature levels (25°C -50°C) used.
Droplet retention or bounce was determined by exposing the angled, adaxial leaf surfaces of greenhouse cabbage and chrysanthemum plants, to a range of spray droplet sizes, in a spray chamber. The spray chamber was constructed so that vertically falling droplets would either be retained by the leaf or would bounce onto adjacent water sensitive papers. The difference between the number of droplets that were sprayed upon the leaf and the number that bounced was used to provide an index of droplet retention for a range of leaf angles and droplet sizes.
The spread of droplets was quantified by using fluorometric analysis to visualize the droplets following their application to the adaxial surface of cabbage leaves. A range of droplet sizes and insecticide concentrations were used. The implications for improved biological efficacy were assessed by preliminary testing against 2nd instar cabbage looper, Trichoplusia ni (Hübner).
The results of these and other experiments are discussed in terms of the advantages and disadvantages to be obtained from the use of an anti-evaporant in pesticide applications.