Efficacy of Two Bole-Injected Systemic Insecticides for Protecting Douglas-Fir From Damage by Douglas-Fir Tussock Moth and Fir Coneworm

One management technique that has been receiving attention for use against various forest insects are applications of bole-injected systemic insecticides. We evaluated the use of two such insecticides (emamectin benzoate applied at a rate of 0.07 ml Al/cm dbh and imidacloprid applied at a rate of 0.1 ml active ingredient (Al)/cm dbh) applied at two different times of the year (fall versus spring) for management of Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough) (Lepidoptera: Lymantriidae) and the fir coneworm, Dyorictria abietivorella (Grote) (Lepidoptera: Pyralidae), insects that cause damage to Douglas-fir foliage and cones, respectively. Spring and fall bole injection of emamectin benzoate significantly reduced survival of Douglas-fir tussock moth caterpillars fed foliage from treated trees and reduced fir coneworm infestations on treated trees compared with untreated controls. Both fall and spring injection periods were equally effective. Douglas-fir tussock moth caterpillar survival was also significantly lowered when they fed on foliage from trees that had received spring injections of imidacloprid. At the dose tested, the fall treatment of imidacloprid did not reduce Douglas-fir tussock moth survival and neither fall or spring treatments significantly reduced infestation levels of fir coneworm. The results suggest that bole-injection treatments of emamectin benzoate can be effective in minimizing insect damage when applied the year prior to foliar feeding or harvest of the cone crop. Imidacloprid appears to be effective only for foliage protection and only when applied during the spring of the year that protection is needed.