Pecan nut casebearer moth, one of its most significant pests of pecan, has a ridge of dark scales running across the forewings. A new guide in the open-access Journal of Integrated Pest Management profiles the pecan nut casebearer and outlines management methods for it. (Photo credit: Jerry A. Payne, USDA Agricultural Research Service, Bugwood.org)

By Allen Knutson, Ph.D.

Pecan is commercially grown across the southern United States, from Georgia to California, as well as in the central U.S. and northern Mexico. New Mexico, Georgia, and Texas lead in U.S. pecan production. Pecan is one of the few plants native to North America that is now an important horticultural crop. As pecan was domesticated, several native insects have become major pests. One of the most important is the pecan nut casebearer (Acrobasis nuxvorella), a small Pyralid moth.

Allen Knutson, Ph.D.

The pecan nut casebearer larva feeds only on pecan and completes all life stages in the tree canopy. Economic loss is due primarily to larval feeding in the spring, just after pollination when the pecan nuts are developing. A single larva can destroy several nutlets during this period. Feeding by subsequent generations can reduce yield.

This week, my Texas A&M University colleague Bill Ree and I have published a new resource on the biology and management of the pecan nut casebearer in the open-access Journal of Integrated Pest Management.

Control of the pecan nut casebearer relies on the use of insecticides. Timing is critical, as insecticides must be applied before young larvae tunnel into the nutlets. Optimal timing for insecticide treatment is determined by scouting the orchard for casebearer eggs and early nut entry by larvae. Scouting the orchard for eggs is tedious, and magnification is often necessary to see eggs hidden in crevices on the pecan nutlet. Also, the egg-laying period may vary by as much as two weeks in the spring.

In the past, pecan growers were uncertain as to when to invest time in scouting. This changed with the identification of the sex attractant pheromone of the pecan nut casebearer and development of pheromone traps, which growers currently use to monitor orchards to determine when casebearer moths become active each spring. A degree-day model was also developed to better use trap data in predicting egg-laying activity, and that model, called PNCforecast, has been made available online so growers had easy access to it. Today, growers can go online and enter their orchard location and date of first moth capture into PNCforecast. The model uses local temperature data to predict when casebearer eggs will be present in the grower’s orchard. Knowing when to scout for pecan nut casebearer eggs saves growers time and increases their confidence in making treatment decisions. The PNCforecast model is accessible via the Southern Region IPM Center.

Pheromone traps help pecan growers know when pecan nut casebearer moths become active in the spring. (Image originally published in Knutson and Ree 2019, Journal of Integrated Pest Managment)

Pecan nut casebearer eggs are difficult to see as they are small, 0.65 millimeters long, laid singly, and secreted in folds and crevices on the pecan nutlet. (Image originally published in Knutson and Ree 2019, Journal of Integrated Pest Managment)

A single pecan nut casebearer larva can destroy all of the nutlets in a cluster. Black frass and silk webbing is characteristic of casebearer damage. (Image originally published in Knutson and Ree 2019, Journal of Integrated Pest Managment)

More than 20 species of parasitic wasps and flies attack the eggs and larvae of the pecan nut casebearer. Conserving these and other natural enemies is important in managing pecan nut casebearer and other pecan pests, including aphids, mites, and other caterpillars. Fortunately, several insecticides are labeled for pecans that provide good control of pecan nut casebearer without impacting most natural enemies. These selective insecticides are a key part of the overall IPM program for pecans.

Pecans are commercially grown in Arizona and California, where pecan is non-native and pecan nut casebearer is not present. Regulatory control through quarantine helps prevent the introduction of pecan nut casebearer through movement of nursery stock and pecan nuts.

Allen Knutson, Ph.D., is a professor in the Department of Entomology at Texas A&M University and an extension entomologist at the Texas A&M AgriLife Research and Extension Center in Dallas, Texas. Email: a-knutson@tamu.edu.