by Dr. Brad Lewis and Irene Calderon

As of May 27, 2008, the Degree-Day model is predicting countable numbers of pecan nut casebearer moths in pheromone traps on or within several days of 12 May. The model also predicts an estimated treatment date for the control of pecan nut casebearer larvae on or within several days of 27 May.

Past accuracy of the degree-day model does not guarantee its accuracy regarding estimated moth emergence and treatment dates for 2008. Treatment decisions should always be based on scouting information.

PECAN NUT CASEBEARER (printable version - pdf)

Damage: Found in all pecan-growing areas, the pecan nut casebearer can cause serious crop loss almost every year if left uncontrolled. Casebearer larvae or caterpillars feed inside pecan nuts. First-generation larvae feed inside small nutlets from April to June. This generation is most damaging, as a single larva often destroys all the nutlets in a cluster. Larvae of later generations require just one or two nuts to complete their feeding, as pecans are larger at that time.

    Biology: The adult casebearer is a gray moth about 1/3 inch long with a ridge of dark scales running across the forewings. The moths are active only at night when they mate and lay eggs on pecan nuts. Most eggs are found on the nutlet tips. Each female lays 50 to 150 eggs during her 5- to 8-day life. The greenish-white to white eggs change to pink or red before hatch.

    Casebearer eggs hatch in 4 to 5 days; young larvae crawl to nearby buds below the nuts to begin feeding. The white empty egg shell remains on the nut. After feeding for a day or two on a bud below the nut cluster, the tiny larvae enter the pecan nut, often tunneling in at the base. Silk and black frass (excrement) are often visible on the outsides of infested nuts. Larvae feed inside pecan nuts for 3 to 4 weeks, depending on the temperature. They are olive gray and reach a length of about inch. Full-grown larvae pupate in the pecan nut; adult moths emerge about 9 to 14 days later.

    The pecan nut casebearer completes several generations each year. Adults of the overwintering generation emerge in April and May and lay eggs on pecan nutlets soon after pollination. First-generation larvae mature to moths, which lay second-generation eggs in grooves on the tips or bases of nuts, or on buds. Second-generation larvae attack the nuts in midsummer about 42 days after nut entry by first-generation larvae.

    Third-generation eggs are deposited on nuts from late July to early September. These larvae feed only in the shucks if the pecan shells have hardened to prevent penetration into the kernel. Many third- and later-generation larvae do not feed, but crawl to the base of a dormant bud and build tough, silken cocoons where they spend the winter.

Peak egg lay often occurs during a 2-week period in late April to early May in the southern and coastal areas, or late May and early June in north Texas. Spring temperatures influence casebearer development; cool, rainy weather can delay moth activity and egg laying. Thus, the egg-laying period can vary as much as 2 weeks from year to year, depending on spring weather.

    There are several ways to determine when to look for first-generation casebearer eggs. One approach is to predict egg-laying activity and nut entry based on spring temperatures and accumulated heat units. To calculate the number of heat units accumulated per day, add each days high and low temperatures (F degrees) and subtract 38. Begin accumulating heat units 10 days before 50 percent budbreak occurs.