Fall Webworms

Nathan Riggs

As spring turns into summer, shade trees are full of leaves and pecan trees are working overtime to produce a pecan crop for fall. Unfortunately for local homeowners and pecan growers, there is a vile enemy that always appears: the dreaded fall webworm (Hyphantria cunea).

Fall webworm moths lay their eggs on the underside of pecan, willow, mulberry and walnut trees in the San Antonio area, but they have over 600 species of favorite trees worldwide. A week later, the eggs hatch and the batch of caterpillars begins enveloping their immediate area in a sheath of silk to protect themselves from hungry birds, paper wasps and other insects.

As they grow over the next four to six weeks, they move to other parts of the tree, eating leaves and expanding their webs as they go. Webworms cause a lot of cosmetic damage, but don’t harm the pecan crop to a large scale.

Some control methods to manage webworms:

  • If reachable, tear open the webs with a pole to allow access by birds and wasps.
  • If reachable, clip off twigs where the webs are located and discard or burn them (if permitted).
  • Purchase some tiny trichogramma wasps from online retailers or local nurseries and release them in your trees during late spring/early summer when eggs are being laid by the moths.
  • For severe infestations, especially on younger trees, consider a spray applied by a professional tree service.

By the time fall rolls around, the caterpillars have spun cocoons within the bark cracks of the tree and begun the metamorphosis to a small white moth and will emerge the following spring.

Pecan trees are a southern staple for stately shape and add wonderful shade to any situation. Webworms are an annual expectation and can be tolerated without too much concern, but are able to be managed with some work.

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