PERSISTENCE OF DIFLUBENZURON ON APPALACHIAN FOREST LEAVES AFTER AERIAL APPLICATION OF DIMILIN

Using a new method for the analysis of diflubenzuron, the active ingre dient in the pesticide Dimilin, the persistence of diflubenzuron on le aves of 20 Appalachian forest trees of 7 species was studied throughou t the 1991 season after aerial application of the pesticide. Composite s were made from leaf samples of each the upper and lower tree canopie s, and replicate subsamples were analyzed for diflubenzuron concentrat ion. The two values closely agreed, confirming composite homogeneity a nd precision of the analytical method. Growth dilution of diflubenzuro n during this study was negligible. A significant loss of diflubenzuro n from the foliage, ranging from 20% to 80%, was observed within the f irst 3 weeks after application. The remaining diflubenzuron was genera lly found to persist for the rest of the growing season until leaf fal l, at which 13 of the 20 trees retained more than 20% of the original pesticide applied. The remaining seven trees, consisting of all five y ellow poplars and two black oaks, showed from 5% to 20% diflubenzuron retention, primarily due to a greater initial crop. At leaf fall, the residual diflubenzuron is delivered along with the leaves to the strea ms and the ground litter underlying the canopy.