This broad category includes several different kinds of insects. All defoliators have chewing mouthparts that allow them to eat the leaves of trees and other plants. Entire trees may be defoliated. Impact of defoliation on black walnut is not completely understood but tree vigor is probably reduced, growth slowed, and the defoliated trees may become more susceptible to attack by other insects or diseases.

FALL WEBWORM,
HYPHANTRIA CUNEA (DRURY)

Description
    The fall webworm is widely distributed throughout eastern United States and feeds on a wide variety of hosts. It is easily recognized by its characteristic web, which encloses one or more branches of a tree and sometimes an entire small tree. Webs begin appearing about mid-July on the outer tips of branches. As the summer progresses, the webs enlarge and become more noticeable. The larvae live inside the web, as many as several hundred to a colony. Very young larvae feed only on the cells of the upper surfaces of leaves but as they grow older they consume entire leaves. Full-grown larvae are usually pale yellow or green with a broad dark stripe down the center back and a yellow stripe down each side..The body is covered with gray or red hairs that measure about 1 inch long. The adult is a white moth with dark spots on the wings.

Injury
    When the insect is abundant, whole trees may be enclosed within webs and eventually defoliated. Defoliation several years in a row may weaken the tree and slow its growth. Defoliated branches are normally not killed and will leaf out again, sometimes within a few weeks.

Control
    Remove webbing and caterpillars by hand when they first become noticeable. It is not necessary to remove the branches. Repeated defoliation over several years' time may require chemical control. Consult your local county extension agent for recommended controls.

GRASSHOPPERS

Description
    Several species of grasshoppers have been reported feeding on black walnut. Grasshopper nymphs and adults are green-colored insects with long hind legs designed for jumping. Adults may be as long as 2 inches.

Injury
    Grasshoppers feed on leaves and are not normally considered a serious pest. However, if a walnut plantation is adjacent to an open field that is cut periodically to produce hay or some other crop, the grasshoppers may move over to the walnut trees after the field crop has been cut.

    Defoliation of trees may occur when grasshopper populations are high.

Control
    If possible, do not grow black walnut trees near open fields where high grasshopper populations are common. Otherwise, consult your county extension agent for recommended controls.

MAY BEETLES,
PHYLLOPHAGA SP.

Description
    May beetles, also known as June beetles or June "bugs", are found throughout eastern United States.

    The adults are oval, robust insects that range in color from light straw to dark brown and in size from 1/2 to 3/4 inch long. The larvae, known as grubs, are milky white and C-shaped; they live underground and feed on plant roots. Adults are most often seen at night flying around lights or into windows and screens during late April, May, and June.

Injury
    The adults feed at night on the newly expanding buds and leaflets of black walnut and other trees. Entire buds may be killed. The beetles also chew holes in already expanded leaves, causing the characteristic shot-hole effect in young leaves in early spring.

Control
    Usually no control is necessary.

PECAN LEAF CASEBEARER,
ACROBASIS JUGLANDIS (LEBARON)

Description
    The pecan leaf casebearer, which is closely related to the walnut shoot moth, is a much less serious pest of black walnut. Both species are commonly found in the same plantation. Because they are nearly identical in appearance, they are best distinguished by their feeding habits.

    Larvae are drab, olive-green with a black head capsule. They grow to 3/4 inch long. Adults are gray-brown moths.

     Newly hatched larvae overwinter in protective cases near the terminal bud. In early spring the larvae leave their cases and move to buds where they begin chewing on the outer surface of the bud scale. Feeding continues as the bud expands. A pile of excrement may conceal a feeding larva but the larva never bores inside the bud. As the larvae grow older and the leaf grows larger, the larvae move to about the middle of the leaf and construct a black trumpet- or cone-shaped case around themselves. From the case, which remains attached to the undersurface of the leaf stem, larvae feed on walnut leaflets.

Injury
    A small amount of defoliation may occur in a tree heavily infested with the pecan leaf casebearer. Normally, however, these insects cause little damage to expanding buds or to leaflets.

Control
    No control is recommended.

WALNUT CATERPILLAR,
DATANA INTEGERRIMA
GROTE & ROBINSON

Description
    The walnut caterpillar is a common pest of black walnut trees throughout eastern United States. The larvae are gregarious, often found in masses on the trunks of trees or feeding on the foliage.

    Very young caterpillars are red with grayishwhite hairs covering the body. Full-grown caterpillars are as long as 2 inches and have a black body with longitudinal yellow stripes along their sides. The entire body is covered with long white hairs.

    The adult moth is brownish gray and has a wingspread of nearly 2 inches. The front wings are marked by curving transverse dark lines.

Injury
    Young caterpillars eat only the outer layer of cells on the lower leaf surface; older larvae consume the entire leaf. Walnut caterpillars are gregarious and feed in colonies. One colony can defoliate an entire young tree in a short time. Often they seem to move down a line of walnut trees, stripping each of its leaves in turn.

Control
    Hand removal of young caterpillars is most effective in preventing further defoliation. If this is impractical, consult your service forester or county extension agent for recommended chemical control.

YELLOW-NECKED CATERPILLLAR,
DATANA MINISTRA (DRURY)

Description
    The yellow-necked caterpillar is closely related to the walnut caterpillar. It feeds on black walnut as well as other forest trees throughout most of the eastern United States.

    Full-grown larvae of the yellow-necked caterpillar are about 2 inches long with a black body and black head. The "neck" area behind the head is characterized by a bright orange-yellow spot. The remainder of the body is marked with four longitudinal yellow stripes interspersed with black, and the entire body is clothed with long, soft, white hairs. The larvae are gregarious and feed in large colonies on leaves near the tips of twigs and branches.

Injury
    Occasional outbreaks of the yellow-necked caterpillar may completely defoliate black walnut trees.

Control
    When outbreaks occur, consult your local county extension agent for recommended chemical controls. Removing larvae by hand is also effective.