ANNAPOLIS, MD (May 18, 2026) ~ Annapolis, MD - The Maryland Department of Agriculture (MDA) is closely monitoring the health of hardwood trees in western Maryland after an early spring frost and outbreaks of defoliating caterpillars have caused damage to emerging leaves. The affected areas include Allegany, Garrett, and Washington counties.

The MDA's Forest Pest Management staff is working in collaboration with the Maryland Park Service and Maryland Forest Service to monitor and map the impacted areas. Large portions of trees in all three counties are expected to remain leafless throughout May and June due to these spring stressors.

The damage caused by the early spring frost was a result of drastic temperature fluctuations in mid-April. Within a span of two days, temperatures went from over 90 degrees to below freezing, causing significant damage to early emerging buds and leaves on hardwood trees between Cumberland and Hancock. Drivers along Interstate 68 between Town Hill and Flintstone will notice a stark contrast between healthy trees on ridgetops and frost-damaged trees in the valleys.

Trees that have been affected by the frost may display shrunken, curled, or brown leaves with dead edges. However, most of these trees are expected to grow new leaves before the end of June unless they were already under severe stress or were very young.

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In addition to the frost damage, widespread leaf damage is also expected due to defoliating caterpillars reaching outbreak levels in Allegany, Garrett, and Washington counties. This will result in many trees appearing bare, similar to how they look during winter months. The caterpillars will leave behind large amounts of silk and droppings that will fall onto anything beneath the affected trees. These impacts will be noticeable until mid-June when the caterpillars move into the soil to pupate.

The following areas are expected to experience defoliation:

- Allegany County: Along 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.

- 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.

The defoliation is being caused by several native species of geometer caterpillars, commonly known as "loopers" or "inchworms." These caterpillars get their name from their unique way of moving by looping their bodies forward as they crawl. However, natural predators such as birds, Calosoma beetles, parasitic wasps and flies, and various diseases have been observed by MDA's Forest Pest Management staff at current outbreak sites this spring. These predators do not pose any risks to humans, livestock, or pets.

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In Garrett County, most of the damage is being caused by fall cankerworms (Alsophila pometari). In Allegany and Washington counties, the half-wing geometer (Phigalia titea) and linden looper (Erannis tilaria) are also responsible for causing damage. It is important to note that while invasive spongy moth caterpillars (Lymantria dispar) cause similar leaf damage, they are not part of this current outbreak.

Despite the damage caused by defoliating caterpillars, it is important to remember that the impacted trees are not dead. They are expected to grow a new set of leaves by late June or early July. However, repeated outbreaks can lead to mortality in already-stressed trees on high ridgetops. The outbreaks in Garrett County have been ongoing for three years now and are likely to collapse soon. However, there is a possibility that these conditions may change and outbreaks could continue. In Allegany and Washington counties, the populations are in their second year and may return next spring. The MDA's Forest Pest Management Program will continue to monitor these populations to track trends for 2027.

For more information on defoliating caterpillars and other forest pests in Maryland, please visit the MDA's Forest Pest Management website.

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