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Problem: Walnut Caterpillar - Datana integerrima
Hosts: Primarily black walnut, pecan, and several species of hickory but may also attack birch, oak, willow, honeylocust and apple.
Description: Walnut caterpillar overwinter as pupae in ground beneath host trees. In late spring, moths emerge and deposit egg masses on lower leaf surfaces. During June and early July, emerged and gregarious larvae skeletonize leaves. Larger hairy brick-red colored larvae consume greater amounts of leaf tissues, and nearly matured gray colored larvae devour entire leaves including petioles.
When disturbed, larvae will arch their both ends of their bodies in what looks like a defensive move. Larvae will crowd together on the lower parts of trees to molt and leave an ugly patch of hairy cast skins. Mature larvae, which are 2 inches in length, descend or drop to the ground where they enter the soil to pupate. A second generation occurs soon thereafter giving rise to the overwintering pupae.
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 near by. Readily available insecticides include carbaryl (Sevin, Sevimol), cyfluthrin (Decathlon, Tempo) and azadirachtin (BioNeem, Margosan-O).
References:
1. Insects and Mites Associated With Shade Trees and Woody Ornamentals, pg 47, K-State Research and Extension Pub S-85
2. Insects That Feed on Trees and Shrubs, Cornell University Press, pg 124
3. Life Histories of Common Insects, Mites and Nematodes Infesting Ornamental Plants in Missouri, Missouri Department of Agriculture, pg F-20
Last Update: 08/22/2005
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