In severe cases trees may be partially or completely defoliated with numerous silken threads covering the entire tree and the ground below. Also, larvae frequently drop to the ground on their silken threads and may defoliate grass or other plants beneath the trees. Even if completely defoliated, however, trees that are otherwise healthy can be expected to recover. Oaks in the Central Valley can be particularly hard hit. However, oakworm is a more serious pest in coastal areas while fruittree leafroller does the bulk of the defoliation damage to oaks in the Central Valley.
Birds sometimes feed on the larvae and pupae but seem to prefer other insects.
These natural enemies often help to keep the fruittree leafroller at low, nondamaging levels, but even in their presence outbreaks of large numbers of leafrollers occasionally occur. Bt, as it is commonly known, is a bacterial preparation that causes a disease in many kinds of caterpillars but does not harm beneficial insects, birds, man, or other organisms. Fruittree leafrollers stop feeding within hours after feeding on a sprayed leaf and die several days later. Thorough spray coverage of the tree is required for control. Caterpillars must ingest the pesticide to be killed.