Panhandle residents have seen caterpillars in abundance this June. One common visitor to pecan trees is the Walnut Caterpillar Datana integerrima. The walnut caterpillar has a very narrow host range and feeds only on trees in the Juglandaceae family which includes walnut, pecan, and hickory trees. They are sometimes seen on other plant material, but feeding on non-host plants is unlikely.
Walnut caterpillar feed on the leaves of host trees through several growth stages and molts until they have reached the final larval instar and are ready to pupate into an adult moth. Their color changes from light green when newly hatched to reddish-brown to almost black with long white hairs as they mature. The caterpillars group together in large masses and may hang from each other and dangle from the tree branches when molting. Instead of creating a cocoon in the tree, the walnut caterpillar moves to the ground beneath the tree and burrows into the soil or leaf litter to pupate and emerges later as a moth.
What can you do if your pecan tree is hosting walnut caterpillars?
Although the numbers seen on trees may be alarming, a healthy tree can tolerate some feeding damage. Stripped branches may increases the chance of a lower yield of fruit because the removal of leaves does reduce the amount of energy the tree can produce, but overall health of the tree should not be significantly affected. However, many homeowners find falling caterpillars and their excrement unappealing and may decide to take steps to manage the population.
There are several natural enemies that feed on caterpillars, so avoid using a broad spectrum insecticide that might harm predatory insects and other animals. Consider using a biological control product such as Bt (Bacillus thuringiensis) that is only lethal to caterpillars. Other methods are “pick and squish” or drowning in a bucket of soapy water. Next year, in the spring, watch for masses of tiny green eggs on the underside of leaves and remove and destroy them before hatching.
For more information visit USDA Forest Service Forest Insect & Disease Leaflet 41 “Walnut Caterpillar”