THE EFFECT OF APPLICATION METHOD ON THE TEMPORAL AND SPATIAL DISTRIBUTION OF NEONICOTINOID INSECTICIDES IN GREENHOUSE ZINNIA AND IMPACT ON APHID POPULATIONS

Greenhouse trials were designed to evaluate the effect the application technique would have on temporal and spatial movement of neonicotinoid insecticides imidacloprid and thiamethoxam through plant tissue. Mature zinnia elegans plants were treated by either a soil drench of neonicotinoid insecticide or foliar application on a single leaf at approximately the midpoint of the plant height. Caged adult aphids were placed on the underside of leaves at five plant heights. Leaves were collected at various post-treatment times along the primary stem of the zinnia to determine levels of insecticide using commercial ELISA kits. Aphid populations were assessed at the time leaves were sampled. Insecticide was detected in all sampled leaves in the drench treatments. Drench treatments reduced aphid populations at all foliar sample locations. On single leaf treated plants, aphid populations were only reduced at the treated leaf and very little insecticide movement was detected. Results demonstrate that the method of delivery of neonicotinoids can have a significant impact on the biological effectiveness. The lack of significant movement of neonicotinoids following foliar application demonstrates the need to provide good spray distribution across the target plant. Drench treatments may provide more effective application options than foliar treatments for treating difficult to reach target areas.