The Worms Are Coming!

by Judy Kautz, OSU Extension Master Gardener

Have you noticed the webs beginning to emerge in trees across our state?  Fall webworms are starting to make their appearance, and they certainly cause our trees to look unsightly.  But do webworms actually harm the trees or are they just a blight on the landscape?

Webworms, or Hyphantria cunea, usually appear on trees in the fall, causing unsightly nests and severe leaf damage. The webworm caterpillar is about an inch long with a black to reddish head and light yellow to greenish body with a mottled stripe of two rows of black and tufts of long whitish hairs. Adults appear as white moths with dark spots on the wings.

Webworm adults are white moths with black spots on their wings.

Webworms are a common occurrence across Oklahoma, but some years they are more noticeable than others. There may be several generations per season and their preferred species are pecan and persimmon trees.  However, you may also find them on other trees including hickory, walnut, mulberry, redbud, American elm, cottonwood and even bald cypress.
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Webs from the webworm may look unattractive, but they usually do not impact a tree's health. Your tree may be totally defoliated by the caterpillars one year and have enough stored energy through photosynthesis to come back next season.  Even then, the long-term impact on the tree is minimal.

The webs themselves are created by a group of worms for protection as barriers from their own natural enemies, like arthropod predators, parasites and birds. Soon the worms will begin to fall from the webs and begin the next stage of their lives, pupating in the soil.

Webworms group together encased in webs to protect themselves from natural predators.

It’s a good idea to remove worms from younger trees, especially those less than two years old. Simply run your hand or a stick down the branch to remove the webs, or prune the branch out.  Be sure to dispose of the worms and webs you remove from the trees. 

There are also a variety of readily available sprays to help with those webs you cannot reach. You need to use a sprayer with enough pressure to penetrate the webbing.  This ensures the spray comes in contact with the caterpillars. Bacillus thuringiensis, commonly referred to as (Bt), is a good spray to use.  It only targets the caterpillars and does not harm beneficial insects like honey bees or other pollinators. You may also use other more broad ranging insecticides but be sure to closely follow all label instructions.

There are some who use a propane torch attached to a long pole to burn out the webs.  Controlling fall webworms using a torch is extremely dangerous!  Especially in our dry conditions, you may very well set the entire tree on fire and that could prove disastrous to your landscape or worse.  Avoid this method entirely!

Here is the safest and most effective method of eliminating webworms:  Prune the tree in the spring and spray with dormant oil spray.  Dormant oil has low toxicity and is readily available in any local garden supply store.   It is particularly effective because it attacks and kills overwintering eggs. Do make sure to clean up any leaf debris to remove these overwintering pupation populations as well.
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Webworms are truly unsightly, but remember. Webs will eventually succumb to the elements.  They only stay attached until wind and rain wash them away!

Fall webworms are beginning to show up in Oklahoma landscapes.

​Do you have a gardening problem?  You can easily obtain help from the Cleveland County Extension Office.  Call (405) 321-4774 and ask to speak to a master gardener or simply come to the extension office.  Bring your problem plant and you will certainly be helped with your issue!