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Master Gardener: No action needed against fall webworms
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Master Gardener: No action needed against fall webworms

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webworms MW

Fall webworms may be unsightly but won’t cause permanent damage to trees.

Every year, I seem to get these caterpillars with large webs in my trees. What can I do to get rid of them? JK

The insect you are describing is known as the fall webworm. Some years, they are really prevalent and seem to be everywhere on almost every tree. But this year isn’t so bad, unless, of course, they are on your trees.

These insects can be found in most of North America, Europe, Asia and northern Mexico. They are present all over Oklahoma but seem to be more prevalent in the eastern part of the state.

The caterpillars (worms) are in the larval stage on their way to becoming a moth. Adult moths are white and have a wingspan of about 1½ inches. Like most moths, they are nocturnal and are attracted to light.

Adults that overwintered tend to emerge in late April to May when females can lay between 400 to 500 eggs each. These eggs are typically laid on the underside of leaves and are almost an iridescent green in color.

In Oklahoma, we tend to have two different varieties of fall webworms. The first one’s eggs begin to hatch in May. These larvae tend to be black and brown. Once hatched, they immediately begin spinning those webs. Their feeding goes on inside the web. The web gets enlarged as they grow to make more food available. These larvae mature and pupate in late June. We have about three generations per year of this variety.

One interesting (if not somewhat creepy) thing about fall webworms is that when disturbed, these caterpillars move in unison, making the web jerk back and forth — something that can be disconcerting if you are unfamiliar with this phenomenon.

The other variety is an orange headed caterpillar. These adults emerge in July, and their larvae are present from July to October. We have two generations per year of this variety. The staggering of their life cycles can make it seem like some years we have webworms all year long.

The second variety tend to prefer pecan trees, but fall webworms have been found on almost 90 varieties of shade, fruit and ornamental trees in the United States. Persimmon and pecan appear to be preferred, but in Oklahoma, black walnut and hickory are also preferred hosts. However, in years with large infestations, they can be found on sycamore, birch, redbud, cottonwood, American elm and bald cypress.

While their webs can be unsightly, they rarely do permanent damage to the tree. Yes, the tree may become nearly defoliated, but this damage tends to occur close to their natural leaf drop time after the trees have stored all the nutrients they need for the winter. However, if the infestation is on a young tree or a tree that is already in distress, there can be permanent damage.

There is a beautiful large pecan tree at the end of our street that seems to get hit every year, but every spring, the leaves are back like nothing happened.

Your best defense against the fall webworm is to keep an eye on your trees. If you catch them early, you can just remove the branch where they are located. Once they get established and begin to spread throughout the tree, control will be more difficult.

Depending on the size of the tree, you can spray with an organic pesticide called Bacillus thuringiensis (BT). To be effective, the caterpillars must eat the pesticide. So you will need to either spray the leaves surrounding the webbing or split the webbing open and spray inside. If it rains, you will need to re-apply the pesticide.

If the infestation is in a larger tree with high branches, there really isn’t much a homeowner can do because we don’t have access to high-pressure sprayers that are able to penetrate the webbing.

There is another variety of caterpillar that tends to get mistaken for the fall webworms, and those are the Eastern Tent caterpillars. These caterpillars tend to be seen earlier in the year and prefer fruit trees, such as black cherry, wild plums, apple and crabapple. You can easily tell the two caterpillars apart because the Eastern Tent caterpillars build their webs in branch forks, while the fall webworms construct theirs at the end of branches. Knowing that distinction can possibly help you win a bet someday. Control for Eastern Tent caterpillars is the same as for fall webworms; however, once again, we generally recommend that you take no action and just let nature take its course.

Yes, their webs can be unsightly, and yes, they can make your trees look terrible. But because they tend not to do any permanent damage to the tree, the best strategy may be just live and let live. Plus, the birds love those caterpillars, so maybe just let them have a delicious snack at the expense of the leaves on your tree. Either way, your tree will likely be fine and just as beautiful next year.


Mickel Yantz, director of collections and exhibitions at the Sherwin Miller Museum of Jewish Art, on the museum’s new Holocaust exhibit


Treat yourself at Tulsa’s top bakeries

Get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th St., or by emailing us at mg@tulsamastergardeners.org.

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