Author: H. C. Ellis, Extension Entomologist
Adults are small, dark-gray moths, 7 to 9 mm long. When at rest, the wings are held roof-like over the body. Newly hatched larvae are whitish to pinkish in color. Older larvae are olive gray then jade green, with yellowish-brown heads. Mature larvae are about 12 to 13 mm long.
In the spring, young overwintering larvae feed on developing buds and then bore into young tender shoots. Newly hatched first generation larvae feed on buds and newly set nuts. Infested nuts are held together by a cluster of silken threads. They are easily recognized by the frass cast out by the larvae. A single larvae may destroy from one to all of the nuts in a cluster. Losses vary considerably from year to year. A light infestation in heavy crop years may provide desirable thinning, but in light crop years, most or all of the nuts may be destroyed.
Nut casebearers overwinter as partly-grown larvae in small tightly woven cocoons (hibernacula), usually at the juncture of a bud and the stem. The larvae become active about bud break in the spring. They feed on buds for a short time, then burrow into tender young shoots. Larvae pupate in tunneled shoots or in cocoons that they attach to other parts of the tree. The F-1 generation of moths emerge in May and are most numerous about the time that nuts are setting. They lay one greenish-white egg per nut cluster, usually on the blossom end of a nut. One moth may lay 50 to 150 eggs.
Newly hatched larvae usually descend from the nut clusters to feed on the buds just below, but return to the clusters after a few days to attack the newly-set nuts. Most casebearer damage is done by these larva. The next generation causes less damage. Each second generation larva normally completes its development within a single nut. Later generations feed mostly in the shuck at the base of the nut and do little damage. There are 3 to 4 generations per year.
When to Control
Casebearer sprays are normally applied when tips of young ”nuts” turn brown (at pollination). However, light infestations do not require control. Monitor adult emergence with pheromone traps placed by mid-April. Begin checking for damage one week after first moth catch. Apply an insecticide for casebearer control if 3% of the nut clusters are infested with eggs and/or larvae. Careful scouting is required. Try to detect infestations before more than one nut per infested cluster is damaged.