PERSISTENCE OF DIFLUBENZURON ON APPALACHIAN FOREST LEAVES IN STREAM WATER

The persistence of diflubenzuron on Appalachian forest leaves placed i n stream water was examined using a new gas chromatographic/mass spect rometric method for analyzing the pesticide. Leaves came from trees ae rially sprayed with Dimilin in the spring and left to weather during t he growing season. The rain exposure minimizes loss of pesticide when the treated leaves are first immersed. After diflubenzuron coverage wa s measured, leaf samples were placed in a headwater stream and residua l diflubenzuron was monitored as a function of time. During July and A ugust, the amount of diflubenzuron on white oak decreased significantl y (by 36% and 23%, respectively) within the first 48 h of stream incub ation, reaching less than 10% of the original concentration within 3 w eeks. In the December studies with yellow poplar, red maple, and white oak leaves, the rate of loss of diflubenzuron was slow. After 54 days in the stream, yellow poplar and red maple leaves retained 45% and 40 %, respectively, of the original diflubenzuron and white oak showed no significant loss. In laboratory experiments mimicking the December fi eld conditions, no significant loss of diflubenzuron was seen from yel low poplar leaves. In view of the persistence of diflubenzuron on hard wood leaves observed throughout the growing season to leaf fall, at lo w stream temperatures, nontarget aquatic organisms that consume these fallen leaves may be exposed to the pesticide for a significant period of time.