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Northwest Iowa Dairy Outlooks

A local discussion of current science and issues concerning dairying in northwest iowa

This week I have had several calls on when to spray for the Pecan Nut Casebearer. Extension Entomologist Allen Knutson notes that the Pecan Nut Casebearer is one of the most important nut-infesting insect pests of pecans. Casebearer larvae tunnel into nutlets shortly after pollination, often destroying all nutlets in a cluster.

The most effective and reliable control method is a well-timed insecticide application(s) made in spring to kill hatching larvae before they tunnel into the nutlets. However, insecticides should be applied only 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 fore-wings. Moths are active only at night, when they mate and lay eggs on pecan nuts. Each female lays 50 to 150 eggs during
her 5- to 8-day life.

Eggs are oval, flat and tiny, just large enough to be seen with the unaided eye. When first laid, eggs are greenish-white or white. Tiny red spots soon appear on the egg, giving it a pink color before hatch. Casebearer larvae are olive-gray to jade green and grow to about 1/2 inch long.

First-generation Casebearer eggs are typically deposited on pecan nutlets soon after pollination. Eggs hatch in four to five days. Young larvae crawl to nearby buds to begin feeding, leaving empty white egg shells on the nut. The tiny larva feeds for a day or two on a secondary bud at the base of a com pound leaf before it enters the pecan nut. Larvae generally tunnel in at the base of the nutlet. Silk and black frass (excrement) are often visible outside infested nuts.

Casebearer larvae feed for about 4 to 5 weeks, depending on the temperature. Full-grown larvae then enter the pupal stage inside the nut. The moth emerges nine  to 14 days later.

The Pecan Nut Casebearer completes two to four generations a year. In this area, overwintering larvae develop into moths that emerge in late 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. Once inside, larvae are protected from insecticide treatments.

Second-generation larvae attack the nuts in midsummer about six weeks after first-generation larvae enter the nut. 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 or fourth-generation larvae do not feed, but crawl to the base of a dormant bud where they build a tough, silken cocoon (hibernaculum) in which to spend the winter. In spring, these immature larvae leave their cocoons and feed by tunneling into shoots. Full-grown larvae pupate in shoot tunnels or in bark crevices. Moths from these overwintering larvae lay first-generation eggs on nutlets.

Homeowners with pecans and producers should be examining nutlets carefully right now for Casebearer eggs. 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. You need a good hand lens 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.

The anticipated date for a management decision on whether or not treatment for Pecan Nut Casebearer is needed is May 31. Examine 10 nut clusters per tree. A cluster is considered infested if it has a Casebearer egg or nut entry. If you find two or more infested clusters before 310 nut clusters are sampled, the Casebearer population is large enough to damage more than five percent of the harvest. Apply an insecticide within the next few days.

If you find fewer than two infested clusters, sample again two to three days later. If you find two or more infested clusters before 310 clusters are examined, apply an insecticide treatment 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 you find fewer than three infested clusters, 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 egg-laying 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. Apply the insecticide one to two days after the first eggs hatch, or as soon as nut entry by larvae is first observed. Delaying treatment maximizes the insecticide’s residual activity. However, consider the time required to treat the orchard and possible delays caused by weather, so that the insecticide can be applied before many larvae tunnel into nutlets.

Be careful when applying insecticide sprays in backyard and urban areas, because spray may drift onto nearby gardens, pets and living areas. In home landscapes, use only products containing spinosad, carbaryl, malathion or Bacillus thuringiensis and that are labeled for pecans.

Before purchasing and applying any insecticide, always read the label to determine if the product is labeled for use on the target plant or site. Follow mixing instructions and safety precautions on the label.

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