Pest description and damage There are many species of moth larvae, including leafrollers and leaftiers, that roll, tie or fold together leaves of ornamental trees, shrubs and other perennials. Leafrollers, when found on native species such as willow, cottonwood, poplar and alder, rarely warrant control since damage is usually cosmetic and short-lived. Mature larvae range between 0.75 to 1.0 inch long. The leafrolling pests can be divided into single-generation moths, such as the fruit tree leafroller and the European leafroller, and two-generation moths, such as the oblique-banded leafroller and three-lined leafroller. The larvae are mostly green or brown caterpillars with a light brown to black head. Adults are rarely encountered, but have distinctive bands or mottling on the wings. Some are noted for their violent backward wriggling - a means of escape. Newly hatched larvae also may work into blossoms and damage developing fruit, which then abort and fall off the plant. The larvae web the leaves and flowers together beginning in late April, and then feed on the developing fruit or flowers. Feeding on the growing points of young plants can promote undesirable branching. Larvae also feed on the surface of ornamental fruit or berries. Leaftiers are similar in appearance, although larvae are up to 0.5 inch long, dirty white, with a brownish head.
Biology and life history The single-generation leafrollers overwinter as egg masses on twigs and branches. Eggs hatch in spring as buds are opening and continue to hatch until petal fall. The larvae feed for four to six weeks, then pupate in the rolled leaves and emerge as moths in early summer. The overwintering eggs are laid in July. Two-generation leafrollers overwinter as immature larvae under the bark on scaffold branches of a variety of host plants. Larvae may feed during warm periods in winter, but are most active in spring with onset of new growth. They feed for several weeks, and then pupate in rolled leaves. Adult moths emerge in late April-May and lay eggs for the next generation. This next generation hatches in early summer and does the most damage.
Pest monitoring Start sampling for leafrollers in mid-April. Examine the new spring leaf growth and terminal clusters for tightly rolled leaves and feeding damage. Look for light-colored clusters of eggs in patches, laid in rows like fish scales, on the bark. Pheromone traps are useful for monitoring adult emergence.
Hand-pick rolled leaves containing larvae or pupae. Removal of overwintering sites, such as rolled leaves on the ground or plastered to tree trunks, can reduce next year's population. Very low temperatures in winter significantly reduce the population of overwintering larvae.
Spiders and parasitic wasps, as well as predators, like the brown lacewing, greatly reduce leafroller populations throughout the year. There are ichneumonid wasps with special adaptations for parasitizing leafrollers.
See Table 3 in:
Chemical Control of Landscape Pests
For more information
Bentley W. J. 2010. Leafrollers on Ornamental and Fruit Trees. UC Statewide IPM Program, University of California, Davis (http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7473.html)
Brunner, J. 1993. Leafrollers: Pandemis leafroller, oblique-banded leafroller, fruit tree leafroller, and European leafroller (treefruit.wsu.edu/crop-protection/opm/leafrollers/