Degree-day model for timing insecticide applications to controlDioryctria amatella(Lepidoptera: Pyralidae) in loblolly pine seed orchards

Abstract

AbstractBecauseDioryctria amatella(Hulst) is a key pest in loblolly pine,Pinus taedaL. (Pinaceae), seed orchards in the southeastern United States, improved timing of insecticide applications would be valuable for its control. To time two fenvalerate (Pydrin® 2.4 EC) applications we tested four variations of a degree-day model that was developed to predicted when various proportions ofD.amatellaeggs would hatch during the spring generation. We compared reductions inDioryctriaspp. cone damage to unsprayed checks and a standard operational spray regime of four monthly applications of fenvalerate. In addition, we examined seeds from healthy cones to determine if sprays to controlD.amatellaalso reduced seed damage caused byLeptoglossus corculusSay (Heteroptera: Coreidae) andTetyra bipunctata(Herrich-Schäffer) (Heteroptera: Scutelleridae). Trials were conducted from 1984 to 1986 in two orchards in South Carolina and one in Alabama. Degree-day accumulations (threshold = 11 °C) were begun on the day when the cumulative number of maleD.amatellaequaled or exceeded five captured in 15 Pherocon 1C® traps baited with 100 μg ofZ-11-hexadecenyl acetate. One application per year was insufficient to controlD.amatellaor reduced seed-bug damage. Two sprays based onD.amatellaphenology significantly reduced coneworm and seed bug damage, and were as effective as four sprays applied monthly. None of the treatments reduce spring cone losses, which are primarily caused byDioryctria merkeliMutuura and Monroe. Several variations of the model performed well, but we suggest that the best, based on efficacy and ease of use, was when sprays were applied immediately after five males were caught (degree-day = 0) and again when the model predicted 50% of the spring generation eggs had hatched.