It’s not exactly a secret at this point but it is abundantly clear that this is going to be another bad year for webworms. Don’t panic. While webworms are unsightly, they do very little long term damage to our landscape plants. Control is suggested only if you are counting on a heavy pecan harvest, have an immature tree that is not yet well established, or have an especially important plant from a visual perspective. This year, as high as the insect pressure appears to be, spraying even these plants may prove to be only marginally effective.
If you do wish to control webworms with a chemical treatment, here are some helpful hints. The insects themselves (caterpillars) can be killed using a number of labeled products, but only if the insect actually comes in contact with the product. The webs, while appearing almost transparent, are remarkably effective at protecting the insects, keeping not only predators away, but liquids as well. For spray treatments to be effective, the web must either be physically broken, or a high-pressure sprayer must be used.
Bt Bacillus thuringiensis subsp. kurstaki is a good product to use because it only kills caterpillars, limiting the losses to beneficial insects like bees. Spinosad is another low-risk product that offers good control. There are several others, just look for webworms on the label. Always remember to read the label and carefully follow the instructions.
We are commonly asked about systemic products, i.e., insecticides that can be applied to the ground and taken up by the tree to fight off the pest. Unfortunately, these just do not work well for the webworm.
In those cases where the outbreak is limited to one or two small trees, with easy access to the webs, pruning them out can be effective. Please do not attempt to burn the webs out! While this can kill the insects, the collateral damage to you or your property is not worth the risk.
For more in-depth information about Webworms indigenous to Oklahoma, see this recent OSU Pest E-alert.
For more information of this or any other horticultural topic, you can contact Keith Reed, the Horticulturist in the Payne County Extension office. Keith can be reached via email at firstname.lastname@example.org, phone at 405-747-8320, or in person at the Payne County Extension office, located at 315 W. 6th in Stillwater.
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