Pecan Pest Seasonal Profiles

Pecan nut casebearer (Acrobasis nuxvorella)

Pecan nut casebearer, empty egg Click image to enlarge		Pecan nut casebearer, damage Click image to enlarge	Pecan nut casebearer egg Click image to enlarge
Pecan nut casebearer damage Click image to enlarge		Pecan nut casebearer damage Click image to enlarge

PECAN NUT CASEBEARER

Damage: The pecan nut casebearer is the most damaging insect pest of Texas pecans. It is found in almost all the pecan growing areas of Texas and can cause serious crop loss every year if left uncontrolled. The casebearer larva or caterpillar feeds 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. A ridge of dark scales runs across the forewings. The moths are active only at night when they mate and lay eggs on pecan nuts. Most eggs will be found on the tips of the nutlets. Each female iays 50 to 150 eggs during her 5- to 8-day life. The eggs are greenish white to white, changing to pink or red prior to hatch.

Casebearer eggs hatch in 4 to 5 days and young larvae crawl to nearby buds below the nuts to begin feeding. The empty egg shell is white and remains on the nut. The tiny larvae feed for a day or two on a bud below the nut cluster and then 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 upon the temperature. Larvae are olive grey to jade green and reach a length of about 1/2 inch. Full-grown larvae pupate in the pecan nut and the adult moth emerges 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 mid-summer 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 construct a tough, silken cocoon in which to spend the winter. In the spring, these immature larvae leave the cocoon, which is called a hibernaculum. They feed on buds and tunnel in developing shoots until they are full-grown. Larvae then pupate in shoot tunnels or in bark crevices. Casebearer moths soon emerge to lay first generation eggs on nutlets.

Control: Insecticide applications must be accurately timed to control newly hatched casebearer larvae before they enter the nuts. Once inside the nuts, larvae are protected from insecticides.

Nuts should be carefully examined for casebearer eggs in the spring to determine if treatment is necessary and to determine the correct timing of the insecticide application. Insecticides should be applied within 2 to 3 days after the first eggs hatch. At this time, the first larvae will begin entering the nuts. Infested clusters can be flagged to monitor egg hatch. By delaying the treatment until the first nut entry occurs, the residual activity of the insecticide is maximized. However, the time required to treat the orchard, and possible delays caused by weather, should be considered so that the insecticide can be applied before significant nut entry occurs.

Often a single, carefully timed insecticide application provides adequate control for first generation casebearers. A second insecticide application may be required if unhatched eggs are found 7 to 10 days after the first application.

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 period of egg laying can vary as much as 2 weeks from year to year depending upon spring weather.

Several methods have been used to determine when to look for first generation casebearer eggs. One of the most successful is the use of a computer model that predicts egg laying activity and nut entry based upon spring temperatures. These predictions are available for most pecan producing areas of the state and can be obtained at your county Extension office. The computer model should not substitute for field scouting for casebearer eggs. The date of first significant nut entry, as predicted by the computer model, is the optimum predicted spray date. Begin scouting for eggs at least a week before the predicted date, as local weather conditions near the spray date can influence egg laying.

Growers should inspect nuts to determine if casebearer infestations are large enough to justify treatment. A sampling plan has been developed to determine if infestations warrant an insecticide application. The plan is based upon the assumption that treatment is justified when infestations are large enough to destroy 5 percent or more of the nuts expected to be harvested. The sampling plans based upon research in Texas. is as follows:

1) Begin searching for eggs at least a week before the predicted date of first nut entry as described above. Tag egg infested clusters to monitor egg hatch.

2) Begin intensive sampling, as described in 3 below, when the first casebearer eggs hatch. This date is predicted by the casebearer computer model but should be confirmed by monitoring actual egg hatch in the orchard.

3) Examine ten nut clusters per tree. A cluster is considered infested if it has a casebearer egg or nut entry. Treat if two infested clusters are found before 310 clusters (31 trees) are examined. If fewer than two of 310 clusters are infested, stop sampling.

4) Sample again 3 to 5 days later or 1 to 2 days before the date of first significant nut entry as predicted by the computer model.

5) Treat if two infested clusters are found before 310 clusters are examined, as before. Otherwise, stop sampling after 310 clusters.

6) Sample a third time 2 days later. A third sample is especially important if cold, rainy nights have delayed egg-laying.

7) If three infested clusters are found before 310 clusters have been inspected on the third sample, then treatment should be considered.

8) Pecan nuts should also be examined for second generation casebearer eggs about 6 weeks after first generation eggs were found. Treatment should be considered if 2 percent of the pecans are infested with eggs.