What are all of these webs doing in my tree?

If you have asked yourself this question over the past several weeks, your tree is most likely a victim of the fall webworm. Despite its name, it is not even a worm at all, but a caterpillar (Hyphantria cunea) that feeds on the foliage of many ornamental trees and shrubs. There are many hosts of this pest, but some local plants include: hickory, pecan, walnut, elm, alder, juniper, mulberry, oak, persimmon, peaches and sweetgum.

Adult moths are roughly an inch long, and white in color with dark spots. Moths are nocturnal, so it is likely that you haven’t noticed them in your tree. In the summer, the webworm starts depositing eggs on the leaves of host plants, and the southern populations can produce four generations in one year. One generation can consist of hundreds of eggs, which is why it is common to see multiple webs in a single tree.

Your control strategy will depend on the point in the life cycle that we are witnessing. What are the options? Rake up your leaves! Removing the material that they use to mature will help prevent future infestations. Often we notice the webworm after the damage is done. Another control strategy is to prune infected branches and crush the webs. A chemical control to consider is applying an insecticide with the ingedient Bacillus thuringiensis, also known as Bt. This control is very effective on small larvae, so the timing of the application should be aimed for the mid-summer months.

Fall webworms can completely defoliate a tree, but sometimes it’s just a few branches. Every situation is different, so consider the extent of the damage before choosing a control strategy. For more detailed information visit the UF/IFAS Featured Creatures website at http://entnemdept.ufl.edu/creatures/trees/moths/fall_webworm.htm.

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