Walnut Caterpillar

Howdy,

  On September 28 TDA extended the cotton stalk destruction deadline for Wharton, Jackson and Matagorda counties to October 15. I've still seen some pickers in the fields, but I'm glad to see this season wrapping up. The cooler weather has at least made harvesting a little more pleasant.

Walnut Caterpillar
Photo: http://entomology.osu.edu/bugdoc/Shetlar/factsheet/ornamental/FSwalnutcat.htm

  Lately I have gotten a few questions on Walnut Caterpillars in the area. These insects feed on a pretty wide variety of woody shrubs and deciduous trees in the walnut family, as well as birch, oak, willow, honeylocust and apple trees. They are native to North America, and range from the eastern United States to Minnesota, Oklahoma, Kansas and Texas. The insect overwinters as a pupa in the soil, and emerges as an adult in the late spring. The females lay egg masses of 600 or more on the underside of leaflets on their host plants. Caterpillars emerge about 9 days after the eggs are laid, and unlike similar looking relatives, these caterpillars do not build webs. Young caterpillars skeletonize leaves, while older caterpillars will consume the entire leaf. After about 23 days, the caterpillars will have molted 4 times, and will then move to the soil to molt into the pupal stage. The last instar (stage between molts) will feed independently rather than with the colony, as they were up until this point. In this area we can have up to 3 generations of walnut caterpillars a year. These caterpillars are usually kept in check by natural predators, and you can achieve some control on small trees by removing the egg masses. On large trees and acreage, insecticides containing Bt or spinosad work well. These work best when applied while the caterpillars are still small, and are applied thoroughly to the entire canopy. For more information check out Bill Ree and Marty Jungman's publication on walnut caterpillars here.
  As always, feel free to contact me if you have any questions or comments.

Sincerely,

Kate Harrell