FALL WEBWORMS Hyphantria cunea (Drury)

Hosts

The fall webworm has been recorded on at least 88 species of shade, fruit, and ornamental trees in the United States. The preferred hosts vary from one area to another. In Oklahoma, persimmon and pecan are most commonly infested and black walnut and hickory are also common hosts. Sycamore, birch, and redbud are often attacked in years of heavy infestations. Infestations on collon wood, American elm, and bald cypress have been reported a few time.

Description

The adult moths are almost pure white and have a wingwpread of about 1.25 inches. Some specimens have the front wings more or less heavily marked with small black spots. Larvae may be pale yellow, yellowish green, greenish, or orange but most have two rows of black spots down the back. The head may be red or black. The body is rather sparsely covered with long white hairs. They are found in webs on the host tree.

Inspection and Control

Small larvae and their small webs may be cut out and destroyed, but larger larvae or those high in trees will need to be treated to achieve control. Sufficient spray pressure is needed to reach and penetrate the webs of these caterpillars. Several insecticides will normally provide control, if adequate spray penetrates the webbing. Also, Bacillus thuringiensis, a bacterial insecticide, has provided control of this insect. Specific chemicals can be found in the OSU Extension Agents Handbook of Insect, Plant Disease and Weed Control (call the Master Gardener office, 746 3701), OSU Extension Facts No. 7306, and OSU Current Report 6209.

Distribution

Found over most of Canada and the United States and into northern Mexico. They are present over all of Oklahoma but are more common ine the east than in the west.

Life Cycle

Adults of the overwintering generation emerge during May or occasionally in lat April. Egg laying occurs in late May and early June. Each female can lay 400 to 500 eggs in masses on the undersides of leaves. The egg masses are covnered with white hairs from the abdomen. Larvae begin hatching in early June and immediately begin to spin the web in which they feed. The web is extended as the larvae grow. The larvae mature and leave the trees to pupate in late July. First generation adults emerge during August and second generation larvae are present from late August into early October. Second generation pupae are the overwintering stage. There are two generations per year.

Damage

Damage is caused by the larvae feeding on the leaves. They rarely are heavy enough to defoliate trees except for young pecans and persimmons. On most forest and shade trees, the insect is detrimental mainly to the beauty of the host, and is thus more of a nuisance than a threat to the health of the tree. Actual damage can occur on pecan as defoliation affects tree vigor, yield, and nut quality. The earlier the defoliation, the more harmful the damage.

References