Numerous stands of western larch, Larix occidentalis, on the St. Joe, Coeur d'Alene, and Kaniksu National Forests, Idaho, show signs of gradual deterioration following repeated defoliation by larch casebearer, Coleophora Zaricella Hbn. (Tunnock et al. 1969). Stand deterioration can occur after 4 years of continued heavy defoliation. The main symptom is epicormic branching. Upon examination, many of these dead and dying larch have been infested by the western larch borer, Tetropium veZutinum LeConte, or infected by root rotting fungi. The objective of this study was to determine if larch severely weakened by larch casebearer feeding would die if they were not attacked by borers or root rots.