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How to control winter moth caterpillars

The winter moth caterpillar is a non-native insect first found in Massachusetts in 2003, and later found in New Hampshire, Maine, Rhode Island and Connecticut, and even the Pacific Northwest. It is a pest of deciduous plants like apple, ash, basswood, crabapple, maple and oak trees

Winter moth caterpillar adults emerge from pupae in mid- to late-November, and can be active into January if temperatures are above freezing. Females deposit 150 to 350 tiny eggs in bark crevices or under bark scales. Egg hatch occurs in early spring, when air temperatures average 55° F.

Newly-hatched winter moth caterpillars crawl up tree trunks and wriggle between bud scales of newly-swelling buds. Injury to trees occurs when the bud scales open and pests move into buds to feed. Larvae continue feeding as they move from bud to bud. Defoliation occurs as older larvae feed in the expanding leaf clusters, and delayed leaf expansion from cool-temperature springs can cause high levels of leaf injury.

Syngenta has conducted trials to determine the effectiveness of Acelepryn® insecticide for controlling winter moth caterpillars and many other caterpillar species. A benefit of Acelepryn is that there are no known adverse effects on beneficial and non-target organisms, including earthworms and honeybees.

Trials included Acelepryn rates of 1 to 8 fl. oz./100 gal. of water. Timing an Acelepryn application is critical because to be most effective, it should be applied prior to insect feeding. Shortly after the small larvae begin feeding and ingesting Acelepryn, they will stop feeding, become paralyzed and die.

Application recommendations
Acelepryn applications should be timed to target trees when their leaves begin to unfold. Higher rates are required when applied at bud burst.

Acelepryn Ornamental Foliar Application Rates

PestProduct per 100 Gallonslb ai per 100 GallonsPPMPercent ai (wt/vol)Maximum Gallons per Acre per Year
Fall Webworm1.0 fl oz0.01315.60.001563840
Gypsy Moth 2.0 fl oz0.02631.30.003131920
Caterpillar4.0 fl oz0.05262.50.0625960
Japanese beetle adults8.0 fl oz 0.1041250.0125480


For more information about winter moth caterpillar control, contact your local Syngenta territory manager

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