By Matthew R. March, MNRD
Polk County Extension Agent
I receive almost weekly inquiries from individuals wanting to increase crop yields on their pecan trees. I understand landowners’ frustrations; they have what looks like healthy and happy pecan trees that fail to produce a significant, if any, crop. Nine times out of 10 yields can be increased by managing for pecan scab and pecan nut casebearer. Pecan scab is a fungus disease that effects pecan trees throughout the south. Since I have spent time writing about pecan scab this past year, I want to now discuss pecan nut casebearer. Pecan nut casebearer is the most economically important nut infesting insect in Texas. The reason why it is so devasting is the larvae tunnel into nutlets shortly after pollination leading to destruction of all the nutlets in the cluster.
The life cycle of a pecan nut casebearer begins when an adult casebearer moth, which is gray to black, lays eggs on nutlets shortly after pollination occurs. Adult moths are active at night and each female will lay between 50-150 eggs. The eggs are barely visible to the naked eye and are oval and flat. Within four to five days the eggs will hatch and will begin feeding on buds. After two days the larvae then tunnel into the pecan nutlet, typically at the base, where they will feed for 4 to 5 weeks. The larvae will then complete metamorphosis into adult moths in the nut before emerging and continuing the cycle. This cycle will repeat itself two to four times during the growing season. Each cycle is considered a generation, with the first generation beginning in the spring. First generation causes the most damage as the larvae feed on developing nutlets in the spring. Second generation can also cause damage during mid-summer as they feed on nuts. Third and fourth generation typically are not of major concern as they usually feed on shucks if the pecan shell has hardened. Additionally, third and fourth generations sometimes do not feed and will crawl to the base of a dormant bud to build a cocoon to survive the winter.
Scouting is essential for management. First generation should receive the most scouting effort due to their potential damage to yield. Additionally, scouting is necessary because once the larvae enter the nut it is protected from insecticide. Nutlets should be carefully examined for eggs during a two-week period from late April to early May. This date will vary depending on weather. Pheromone traps are also useful in scouting as they can be used to anticipate when eggs will be laid. By using traps to catch and monitor for adult moths you can then predict when to begin checking for eggs on nutlets. Once adult moths are captured you should begin checking for eggs seven to 10 days later.
By performing scouting and monitoring you will be able to determine if infestation levels justify an insecticide treatment. For commercial production, insecticides with active ingredients of pyrethroid and carbaryl are recommended. For residential and homeowners, insecticide options include Spinosad (Green Light Lawn and Garden Spray with Spinosad), carbaryl, malathion and Bacillus thuringiensis. As a reminder, only use products labeled for pecans and always follow the label