Forest Health Protection, Southern Region

Importance. - The fall and spring cankerworms defoliate a variety of hardwood species in the spring. Hosts include the red and white oak groups, maples, elms, hickories, ash, and cherry. Heavy defoliation usually occurs in May and June, and can cause growth loss, mast reduction, and, if coupled with other stresses, may result in mortality. Their greatest impact is often felt in high public use areas where defoliation reduces the aesthetic value, and larvae and their droppings create a nuisance.

Identifying the Insect. - The wings of male moths are light gray to tan, with wavy lines, and span about 1 to 1 1/2 inches (25 to 37 mm). Females are wingless.

Mature larvae of the fall cankerworm are about 1 inch (25 mm) long and vary from light green to black, with light yellow lines on the sides and a dark dorsal stripe. Mature larvae of the spring cankerworm are 4/5 to 1 1/2 inches (18 to 30 mm) long and range in color from reddish to yellowish brown, yellowish green, or black. The head is light and mottled with a yellow stripe along each side of the body. Coloring of both loopers varies with population density.

Identifying the Injury. - Small holes in the leaves are early evidence of young larvae feeding on expanding foliage. Older larvae consume the entire leaf, except the midribs and major veins.

Biology. - Fall cankerworm adults emerge in the fall following a hard freeze. They overwinter in the egg stage. The spring cankerworm adults emerge in February and March to lay their eggs. For both species, the eggs hatch at about the time of bud break, and the young larvae begin feeding on the new foliage. Feeding continues for approximately 6 weeks, after which the mature larvae enter the soil and pupate.

Control. - The eggs and larvae are attacked by insect parasites and predators. Other natural enemies also help in control. Sticky bands placed around the trunks of high value trees can trap the females as they climb the tree to lay their eggs. In high use or high value areas, chemical control may be needed.