Catoctin Mountain Park - Pests (U.S. National Park Service)

(photo by Jeremy Murphy)

Tree defoliation from gypsy moths

Gypsy Moth
Since its accidental introduction in eastern Massachusetts in the late 1860's, the European strain of the gypsy moth (Lymantria dispar L) has been spreading. In 1994 it was considered a permanent resident in 16 northeastern states.
The gypsy moth caterpillar can be extremely disruptive to the forest ecosystem. Caterpillars feed on the leaves of hardwood trees, particularly oak, which can result in complete defoliation of the tree. Defoliation reduces the vigor and general health of forests and shade trees, leads to tree death which can alter wildlife habitat and change water quality and quantity.

Some years the gypsy moths experience a population explosion. These natural cycles are known as outbreaks, and it is during these years that defoliation becomes a serious problem. It is said that during these peak years you can actually hear the caterpillars feeding in the forest. One resource management employee stated that "it sounds like it's raining on a sunny day" as the droppings fall to the forest floor.

Catoctin Mountain Park, like most of the Appalachian forests, has been affected by the gypsy moth. In 1981 the USDA Forest Service, Forest Pest Management staff from Morgantown, West Virginia joined with Catoctin to monitor and manage gypsy moth populations. That first year's activities included several egg mass surveys and a defoliation survey. Egg mass size is an indicator of the status of a gypsy moth infestation. Declining outbreaks are characterized by the presence of many small masses (approximately 0.5 in long) that contain as few as 75 to 100 eggs. In static or growing populations, the egg masses are fewer in number but larger (1.5 in long) and contain from 700 to 1,000 eggs. In 1981 egg mass densities exceeded 5000 per acre in certain areas. The following year marked the first time an aerial application of insecticide was used on National Park Service property to control gypsy moth.

From 1982 through 1990 treatment was continued where gypsy moth concentrations were high. This varied from as few as 300 acres in 1986 to 6000 acres in 1983. In 1987 tree defoliation was limited to only 48 acres. From 1991 through 1999 the gypsy moth population was very low and no treatments were required. However, in 2001 the population once again increased to a dangerous level requiring treatment for 800 acres on the east side of the park. This was followed by a treatment of 401 acres in 2002 located just east of the 2001 treatment area. Gypsy moth continues to be a problem that is a management priority, on the east side of the park. A total of 42 acres of forest were defoliated this year even after the previous two years of treatment.

Hemlock Wooly Adelgid
The hemlock woolly adelgid (Adelges tsugae) is another pest that is affecting Catoctin. Introduced from Asia in 1924 this insect primarily attacks eastern hemlock and Carolina hemlock trees. The hemlock wooly adelgid injures a hemlock by sucking sap from the young twigs causing needles to discolor and drop prematurely. Complete defoliation and tree death can occur in a few years.

An infested hemlock tree will have white cotton swab-like sacs at the base of the needles. These egg sacs are present throughout the year, but are most prominent in the spring. This insect is easily spread to uncontaminated areas by wind, birds, and mammals.

Many hemlocks in the park have succumbed to the hemlock woolly adelgid. At one time, hemlocks had shaded the riparian areas of Big Hunting Creek, now the trees are mere skeletons. The loss of hemlocks around these riparian areas could possibly change the water quality of the stream and in turn affect the native brook trout that depend on its clean, shaded waters.

Efforts have been made to control the adelgid in the park. An experimental treatment using horticultural oil was applied to several hemlocks in Camp Round Meadow in 2001. Another control effort, injecting 50 mature hemlock trees with an insecticide, was tried in 2002. Results of these treatments will be evaluated over the next two years. Another control alternative that may be applicable at Catoctin is to release the tiny black predator beetle, Pseudoscymnus tsugae. This beetle, native to Asia, is related to the common native ladybug and only preys on adelgids. Release of this beetle may save the hemlocks from total destruction. This management strategy is currently being considered by park management. Efforts to save the hemlocks are being done in conjunction with Ecoscientific Solutions .