The Maryland Department of Agriculture is monitoring hardwood trees in western Maryland following an early spring frost that damaged emerging leaves in Allegany County, along with outbreaks of defoliating, or leaf-eating, caterpillars in Allegany, Garrett and Washington counties.
Because of these spring stressors, large areas of trees across all three counties are expected to appear leafless through much of May and June. The department’s Forest Pest Management staff is working with the Maryland Park Service and Maryland Forest Service to monitor and map the affected areas.
Frost damage
In mid-April, large temperature fluctuations occurred, going from over 90-degrees to below-freezing within a period of two days.
The drastic temperature changes damaged early emerging buds and leaves on hardwood trees between Cumberland and Hancock as cold air settled in the valleys. Drivers along Interstate 68 between Town Hill and Flintstone will notice a clear difference between healthy trees on the ridgetops and frost-damaged trees in the valleys, agriculture officials said.
Damaged leaves may appear shrunken, curled or brown in appearance, often with dead, crinkled edges. Most affected trees are expected to grow new leaves before the end of June unless they were already heavily stressed or very young.
Defoliating caterpillars
Widespread leaf damage to hardwood trees, especially oaks, is expected throughout May and June as defoliating caterpillars are likely to reach outbreak levels in Allegany, Garrett and Washington counties. Many trees will appear bare, similar to how they look during the winter months.
The caterpillars will leave behind large amounts of silk and droppings that will fall onto anything beneath the trees they are feeding on. Residents will notice these impacts until the caterpillars move into the soil to pupate in mid-June.
Defoliation is expected in the following areas:
- Washington County: Along the west side of South Mountain, visible from Annapolis Rock and Black Rock overlooks, and in the northwest section of Greenbrier State Park.
- Allegany County: Along the ridgetops of Town Hill, Green Ridge and Polish Mountain in Green Ridge State Forest.
- Garrett County: Near Grantsville and along the ridgetop of Meadow Mountain from Deep Creek Lake to Keyser’s Ridge, extending north to the Pennsylvania line.
Defoliation is being caused by several native species of geometer caterpillars, commonly referred to as “loopers” or “inchworms,” which emerge in the spring to feed on new leaves. These caterpillars get their name from the way they move, looping their bodies forward as they crawl.
Natural predators to these species of caterpillars include birds, Calosoma beetles, parasitic wasps and flies, and various naturally-occurring diseases. These predators, parasites and diseases have all been seen by the department’s Forest Pest Management staff at current outbreak sites this spring. They pose no risks to humans, livestock or pets.
In Garrett County, most of the damage is being caused by the fall cankerworm (Alsophila pometari). In Allegany and Washington counties, damage is also being caused by the half-wing geometer (Phigalia titea) and linden looper (Erannis tilaria). While invasive spongy moth caterpillars (Lymantria dispar) cause similar leaf damage, they are not part of this outbreak.
Trees impacted by defoliating caterpillars are not dead and are expected to grow a new set of leaves by late June–early July. However, repeated outbreaks, especially in already-stressed trees on high ridgetops can lead to mortality.
Outbreaks in Garrett County are now in their third year and are likely to collapse. However, these conditions may change and outbreaks could continue. Populations in Allegany and Washington counties are in their second year and may return next spring. The department’s Forest Pest Management Program will continue monitoring populations to track trends for 2027, officials noted.
For more information on defoliating caterpillars and other forest pests in Maryland, readers may visit the department’s Forest Pest Management website.
