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Ray Ridlen: Walnut caterpillar can harm trees

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.
Oklahoman Published: July 26, 2014
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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.

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