when they mate and lay eggs on pecan nuts. Each female lays
50-150 eggs during her 5-8 day life.
L-5134
The pecan nut casebearer is one of the most important nut infesting insect pests of pecan. It is found in almost all the pecan growing areas from the east coast to southeast New Mexico. Casebearer larvae tunnel into nutlets shortly after pollination, often destroying all of the nutlets in a cluster. The most effective and reliable method of control is a well-timed insecticide application(s) made in the spring to kill hatching larvae before they tunnel into the nutlets. However, insecticides should only be applied if infestations and nut load justify treatment.
The adult casebearer is a gray to almost black moth about 1/3
inch long. A ridge of dark scales followed by a band of lighter
color runs across the forewings. Moths are active only at night
when they mate and lay eggs on pecan nuts. Each female lays
50-150 eggs during her 5-8 day life.
Eggs are oval shaped, flat and very small (.36 X .65 mm), just large enough to be seen with the unaided eye. Eggs are greenish white or white when first laid. Tiny red spots soon appear on the egg giving it a pink color prior to hatch. Casebearer larvae are olive-gray to jade green in color and reach a length of about 1/2 inch in length.
First generation casebearer eggs are typically deposited on pecan nutlets soon after pollination. Eggs hatch in 4-5 days and young larvae crawl to nearby buds to begin feeding. The empty egg shell is white and remains on the nut. The tiny larva feeds for a day or two on a secondary bud at the base of a compound leaf before it enters the pecan nut. Nut entry is generally at the base of the nutlet. Silk and black frass (excrement) are often visible on the outside of infested nuts.
Casebearer larvae feed for about 4-5 weeks, depending upon temperature. Full-grown larvae then enter the pupal stage inside the nut. The moth emerges 9-14 days later.
The pecan nut casebearer completes 2-4 generations each year. Adults of the overwintering generation emerge in April and May and lay eggs on pecan nutlets soon after pollination. These eggs result in first generation larvae which feed on nutlets and generally cause the most damage.
Second generation larvae attack the nuts in mid-summer about 6 weeks 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.
Many third and, if present, 4th generation larvae do not feed, but crawl to the base of a dormant bud where they construct a tough, silken cocoon (hibernaculum) in which to spend the winter. In the spring, these immature larvae leave the cocoon and feed by tunneling into shoots. Pull-grown larvae pupate in shoot tunnels or in bark crevices. Moths from these overwintering larvae lay first generation eggs on nutlets.
First generation larvae usually have the potential to cause economic loss. For this reason, control is directed primarily at this spring generation.
Insecticide applications must be accurately timed to control newly hatched casebearer larvae before they enter the nuts. Once inside, larvae are protected from insecticide treatments.
In the spring, nutlets should be carefully examined for casebearer eggs to determine 1) if egg infestations are great enough to justify treatment and 2) the optimum timing of an insecticide application.
The period of peak egg lay often occurs during a two week period in late April to early May in the southern and coastal areas of Texas and late May and early June in north Texas.
When egg lay occurs is weather-related because spring temperatures determine how quickly the overwintering generation develops. Pecan producers often know from years of experience when casebearer eggs are likely to be found in their orchards. However, egg laying can occur earlier during warm springs and can be delayed during cool springs.
One method of predicting egg lay is the use of a computer model developed at Texas A&M which uses heat units or degree-days. Temperature data are compiled from cities throughout Texas and used in the model to predict the date when the first significant nut entry by casebearer larvae will occur. This date is the predicted optimum spray date. These predictions can be obtained from your county Extension office.
Computer predictions are best used to determine when to look for eggs and to plan insecticide applications. Orchard scouting for eggs should begin a week before the predicted spray date as unusual weather conditions near the spray date can accelerate or delay egg laying activity.
Most casebearer eggs are found at the tip of the nutlet, either on the top (stigma) or hidden just under the tiny leaves (sepals) at the tip of the nutlet. A good hand lens is necessary to identify casebearer eggs and determine their development (hatched, white or pink). Also, look for bud feeding just below the nut cluster to detect the presence of newly hatched larvae.
As described above, begin scouting for eggs 7-10 days before the date of first nut entry as predicted by the computer model. The following sampling plan can be used 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.
About 2-3 days before the predicted first significant nut entry date, or when 1730-1760 heat units have accumulated, examine ten nut clusters per tree. A cluster is considered infested if it has a casebearer egg or nut entry. If, on this date, two or more infested clusters are found before 310 nut clusters are sampled, the casebearer population is large enough to damage more than five percent of the nuts expected to be harvested. An insecticide should be applied within the next few days.
If fewer than 2 infested clusters are found, sample again two to three days later (or when heat units total 1831). If two or more infested clusters are found before 310 clusters are examined, an insecticide treatment should be applied without delay.
If no treatment is indicated, sample again two days later. A third sample is especially important if cold, rainy nights have occurred which can delay egg-laying. If less than three infested clusters are found, treatment is not warranted. Infestations of three or more infested clusters at this time indicate some damage may occur. Consider the effect of rainy weather on oviposition and crop load in making treatment decisions at this time.
Nut clusters with eggs can be tagged with a piece of ribbon and checked each day to determine when hatch occurs. The insecticide should be applied 1-2 days after the first eggs hatch, or as soon as nut entry by larvae is first observed. By delaying the treatment, the residual activity of the insecticide is maximized. However, time required to treat the orchard, and possible delays caused by weather, should be considered so that the insecticide can be applied before many larvae tunnel into nutlets.
Backyard Trees - Urban Areas
Insecticide sprays should be applied with caution in backyard and urban areas because of the great potential for spray drift onto nearby gardens, pets and living areas. Only products containing carbaryl, malathion, chlorpyrifos or diazinon which are labeled and packaged for homeowner use should be used for control in urban areas. Some commonly available formulations for homeowner use on pecans are:
| carbaryl: Green Light® Sevin 25%; | |
| ..... | Ortho Sevin 27% |
| chlorpyrifos: Green Light® Termite and Insect | |
| Pest Killer, 12.6 % | |
| malathion: Green Light® General Spray, 50% | |
| diazinon; Spectracide® Lawn and Garden, 25% | |
Refer to label instructions for mixing, application rates and precautions.
Commercial Pecan Production
There are many insecticides labeled for use on pecans for controlling pecan nut casebearer. The choice of insecticide should be based upon applicator safety, grazing restrictions if livestock are present, and potential impact of the insecticide on other pests. The use of the pyrethroid insecticides (Ammo®, Cymbush®, Asana XL®) or carbaryl (Sevin®) has sometimes been followed by outbreaks of aphids or spider mites in pecans. For this reason, the use of pyrethroid insecticides for the pecan nut casebearer is discouraged, especially if the orchard has a history of aphid outbreaks following their use. If pyrethroid insecticides are used, they should be applied no more than once per season.
Two insecticides, Javelin® WG and Dipel® ES, have recently been labeled for control of pecan nut casebearer in pecan. The active ingredient in these insecticides is the toxin of the bacteria Bacillus thuringiensis, or B.t., which kills only caterpillars of moths and butterflies. Because of this specificity, Javelin® WG and Dipel® ES have low toxicity to humans, wildlife, and beneficial insects and treated orchards can be grazed. These microbial insecticides are degraded by sunlight, so they provide a shorter period of residual control than some other insecticides. Also, unlike some insecticides, the B.t.s do not kill casebearer moths. Accurate treatment timing to target hatching larvae and thorough spray coverage are especially critical for good control with B.t. insecticides.
There is limited information on the effectiveness of these B.t. insecticides for casebearer control in commercial production. Preliminary studies indicate good control of light to moderate infestations, but further testing is necessary.
Additional insecticides labeled for controlling casebearer include: chlorpyrifos (Lorsban®); azinophosmethyl, (Guthion®, several formulations) and endosulfan (Thiodan®).
Many kinds of insects and spiders that occur naturally in pecan trees feed on the pecan nut casebearer. Some of the most important natural enemies are tiny parasitic wasps that sting and kill the larval stage. Over 25 different species of wasps are known to attack casebearer larvae and although little is known about these beneficials, they no doubt help reduce casebearer populations.
Very tiny parasitic wasps of the genus Trichogramma lay their eggs inside the casebearer egg. The wasp egg hatches and the Trichogramma completes its entire development inside the casebearer egg, turning the egg black. Trichogramma wasps occur naturally but little is known about their importance in controlling pecan pests. Trichogrammma wasps can be purchased for release in orchards but studies to date indicate that currently available species and methods of release do not provide effective control of casebearer.
Major funding for this publication was provided by the Western Pecan Growers Association. Additional funding was also provided by the Texas Department of Agriculture.
5M-7-95, Reprint
ENT 4
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Last modified: April 30, 1997 by Edgar Cross