Seeing leaves on your fruit trees rolled up like a sandwich wrap? Could be leafrollers, a family of insects that attack the leaves of fruit trees like apples, pears, and peaches. They also target some ornamental trees like ash, poplar, and oak.
Leafroller larvae feed on tender, new leaves, giving them a ragged appearance; they also roll and tie leaves together with silken threads to form compact hiding places. Some years very large populations develop. In severe cases larvae can partially or completely defoliate trees, and their numerous silken threads can cover the entire tree and the ground below. Also, larvae frequently drop to the ground on their silken threads and can defoliate other plants beneath the trees. However, even completely defoliated trees can recover if they are otherwise healthy, with the exception of newly planted and first-leaf trees.
While they may be a nuisance, leafrollers are an important part of the food chain and have many natural predators, including several species of parasitic flies and wasps. Lacewings, assassin bugs, ground beetles, and spiders are also predators of this pest. Birds sometimes feed on the larvae and pupae, although they usually prefer other insects. These natural enemies often help to keep leafrollers at low, nondamaging levels, but even if natural enemies are present, large outbreaks of leafrollers occasionally occur. If you create a welcoming environment for beneficial insects, they will naturally help control the population of pests like leafrollers.
If you have these pests, start by removing the affected leaves. These leaves are easy to spot because they are rolled up and often webs secure the leaves together. Removing rolled leaves effectively and immediately gets rid of the leafroller habitat.
The microbial insecticide Bacillus thuringiensis, 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, humans, or other organisms. Leafrollers stop eating within hours after feeding on a sprayed leaf and die several days later. Thorough spray coverage of the tree is required for control. Bt is most effective on leafroller larvae when they are small (less than one-half inch long) and usually requires more than one application. Caterpillars must ingest the pesticide to be killed.
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