The last couple of weeks we have been receiving many calls about caterpillars in pecan trees. Most people are familiar with fall webworms in Oklahoma and many were around for the 1997 fall Webwormzilla outbreak.
I thought this would be a good timely article to familiarize you with the walnut caterpillar — datana integerrima.
Hosts: The larvae feed only on foliage of trees of the family Juglandaceae. Hosts include black and English walnuts, butternut, pecan, and various species of hickory.
Damage: These large caterpillars can defoliate the trees and severely affect tree vigor, yield and nut quality. The earlier the tree is defoliated, the more harmful the damage to the tree. Trees can withstand two or three consecutive years of heavy defoliation before they die. Epidemics seldom last longer than two years in any one location.
Life cycle: There are two generations of this pest per year in Oklahoma. Moths emerge from mid-May to early June and in late July and early August. Larvae feed on the leaves in June and July and from late August into October.
The larvae are gregarious and feed in groups, but do not spin webs in which to feed. Small larvae skeletonize the leaves but larger larvae consume all but the petiole. They migrate back to the trunk or larger limbs in groups each time they are ready to shed their skins. Mature larvae leave the trees and pupate in the soil. Pupae of the second generation overwinter.
Description: Walnut caterpillar moths are light brown with four narrow, brown bands on each front wing and a dark red brown thorax. The wingspan is about 1 3/4 inches. The larvae are dark red when young but become black near maturity.
They have many long, white hairs on the body. When disturbed, they usually raise the front and back thirds of the body. Mature larvae are about 2 inches long. The eggs are round and white and are laid in loose masses on the undersides of leaves. This species is often called the walnut datana.
Recommendations: Literature cites the removal of leaves with egg masses as a means of controlling walnut caterpillar. This may prove impractical where large trees are involved or numbers of infested leaves are present. Bands of tree Tanglefoot could be used to ensnare larvae as they migrate to main branches or the tree trunk to molt.
Chemical controls may provide the most practical means of control. Look for early signs of feeding on the ends of the branches. Larvae should be nearby. The organic control spinosad is preferred and is found in Conserve; Fertilome Borer, Bagworm, Leafminer & Tent Caterpillar Spray and Captain Jack’s Dead Bug Brew. Sevin or any of the synthetic pyrethroids (permethrin, cyfluthrin) may also be used but will also kill walnut caterpillar predators.
The following workshop will be held at the OSU Extension Center, 930 N Portland. It is free and open to the public. Questions? Call 713-1125.