Potential Douglas-fir tussock moth damage in northern Idaho in 1974 based on a 1973 fall egg mass survey

Abstract

An epidemic of Douglas-fir tussock moth was detected in northern Idaho in 1972. In 1973, aerial surveys showed that nearly 100,000 acres contained various degrees of visible defoliation. An egg mass survey of five reporting units made in the fall of 1973 determined potential for damage in 1974. Based on new egg mass densities and new to old egg mass ratios, damage is predicted to be sufficiently high to warrant control on 34,138 acres in the Coeur d'Alene unit, 64,779 acres in the St. Joe unit, 4,433 acres in the Clearwater unit, 4,762 acres in the Craigmont unit, and 33,501 acres in the Nezperce unit. Total acres qualifying for treatment are 141,613. In addition, some damage might occur on 81,554 acres within the five units. These areas will be further evaluated to determine if they qualify for treatment