Leaf crumpler is a common pest in ornamental landscapes and on nursery plants. Although their ugly masses are not very noticeable, this is the best time to control this caterpillar and prevent heavy damage next year. Heavy infestations tend to occur on the same plants year after year.
Leaf crumpler attacks cotoneaster, crab apple, pear, hawthorn, pyracantha, and privet. Small (first-instar) caterpillars (larvae) skeletonize leaves, but as the caterpillars increase in size, they consume all plant tissues except the midrib. Mature caterpillars are about 3/4 inch long. Caterpillar feeding is greatest in June and early July.
Caterpillars construct cases made of dead leaf fragments, silk webbing, and frass pellets that are attached to twigs and branches. Cases may be almost 2 inches long. These habitats make the host plant appear ugly. Leaf crumpler uses these cases to hibernate and pupate. The cases may remain on plants for several months after moths emerge. Moths (adults) emerge in late June with peak emergence in mid-July. Adult females lay eggs from late July to August. Eggs are laid either individually or in masses along the veins on the leaf underside. Females live for approximately 10 days. The insect overwinters as larvae, and there is one generation per year.
Pruning out or destroying cases can manage small populations of leaf crumpler. Materials that can be used to control leaf crumpler include Bacillus thurin-giensis kurstaki (Dipel), diazinon, and lambda-cyhalothrin (Scimitar). Bacillus thuringiensis works best on young caterpillars; it must be ingested to be effective. Diazinon and lambda-cyhalothrin work by contact, so thorough plant coverage is essential. All materials mentioned must be applied in the late summer and early fall before the caterpillars hibernate in the cases. Diazinon and Scimitar should also be effective in the spring when the caterpillars start to feed again.