Description of leaf crumplers
The leaf crumpler is an occasional caterpillar pest in ornamental nurseries and landscapes. It is most commonly found on Cotoneaster but may occur on crab apples and other plants. The larvae consume the leaves during the late summer and again the following spring. As they feed they construct a protective habitat made of dead leaf fragments, silk webbing and frass pellets. The disagreeable appearance of the webs is often more significant than the leaf consumption.
Life cycle of leaf crumplers
Leaf crumpler larvae live in the protective cases attached to twigs and branches. They forage away from the case and carry back leaves to consume. Leaves are usually eaten down to the midrib; unconsumed leaf fragments are incorporated into the case. The cases remain on the plant making it look ugly long after the caterpillars have finished feeding and emerged as moths.
The leaf crumpler has one generation per year. Moths emerge in early July to lay eggs. The resulting caterpillars feed during the remainder of the summer, hibernate inside the cases through the winter and resume feeding the following spring, usually in late April.
Management of leaf crumplers
Appropriate controls include pruning to remove heavily infested twigs during late summer and winter. Parasites and natural controls often limit the occurrence of this pest, though significant infestations may persist for a year or more. Insecticide sprays can be used for prevention and control. The best time to treat would be in late July while the larvae are still small, although sprays at other periods of active feeding, including just after leaf emergence in the spring, should be effective. Suggested insecticides include Bacillus thuringiensis, Sevin or permethrin.