The most effective timing for control of the Nantucket pine tip moth, Rhyacionia Frustrana (Comstock), was determined by treating a series of plots with dimethoate on different dates in 1981 and 1982. The best control date in each of three generations was related to percent egg hatch, instars present, and location of larvae. Optimum control coincided with 70 to 80% egg hatch for generations 1 and 2. One application of dimethoate did not provide acceptable control in generation 3, but the lowest infestations occurred when application was made at ca. 55% egg hatch. Optimum times for control with dimethoate were similar in 1981 and 1982. Two applications of dimethoate in generation 3 gave good control. Preliminary tests of fenvalerate in 1982 showed that it provided better control than dimethoate and that it must be applied earlier than dimethoate for best results.