Maryland Departments of Agriculture and Natural Resources Confirm Fall Cankerworm Outbreak in Garrett County

ANNAPOLIS, MD (May 29, 2024)– The Maryland Department of Agriculture and Maryland Department of Natural Resources have confirmed an outbreak population of fall cankerworm (Alsophila pometari) in Garrett County caused heavy defoliation of hardwood trees on Meadow Mountain in Deep Creek Lake State Park. Defoliation is visible from Glendale Bridge and extends north from State Park Road. The Maryland Department of Agriculture Forest Pest Management, Maryland Park Service, and Maryland Forest Service are working together to map and monitor the ~700-acre outbreak. Outbreak populations of this caterpillar are also occurring north of Route 68 near Keysers Ridge.

Fall cankerworm is a native caterpillar that occasionally reaches outbreak populations. Defoliation is similar to that of the invasive spongy moth (Lymantria dispar dispar), but has a different appearance. Spongy moth caterpillars are 3 inches or more and hairy, whereas fall cankerworm caterpillars are 1-2 inches long, smooth, and move in a classic “inchworm” pattern.

The affected area will look like winter in summer; trees affected by outbreak populations of fall cankerworm will have all their leaves eaten, usually with only the leaf midvein remaining. The trees are not dead and will grow a new set of leaves by late June and early July. Repeated cankerworm defoliation, especially in stressed trees on high ridge tops, can cause mortality. However, unlike a spongy moth outbreak, natural enemies like birds, Calosoma beetles, parasitic wasps, and various naturally occurring diseases usually cause high populations of fall cankerworm to crash before major tree mortality occurs.

Park patrons should expect large numbers of ~1-2 inch caterpillars hanging from the trees on silk threads, and falling to the ground in these areas. Defoliation, caterpillars, and frass (caterpillar droppings) will be particularly noticeable near the Thayerville lookout tower and along the Western portion of the Meadow Mountain Trail. Caterpillars will remain in the area until mid-June when they begin to pupate in the soil.

For more information on fall webworm and other forest pests in the State of Maryland, please visit the Maryland Forest Pest Management website at https://bit.ly/45cbEhH.

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