Through my travels during the last few weeks I have noticed that fall webworms have begun to appear on many pecan trees across Sampson County. This arrival isn’t necessarily early; however, it is earlier than in previous years.
From May to July, female moths will lay approximately 900 eggs on the underside of host leaves. The main hosts in our area are pecan, persimmon, sourwood, and willow. If you have any of these tree species in your landscape, expect these unwanted visitors. The eggs will hatch within a few weeks, and the larvae begin to spin silken webs over the leaves beginning at the tips of the branches. As the larvae grow, webs enlarge and enclose more foliage. Large portions of tree branches are commonly enclosed by the webs and become an eyesore later during the summer. The larvae will feed for 4 – 6 weeks in the protection of their webbing. After feeding, the larvae will drop to the ground where they tunnel into the soil and pupate. Within a few weeks the adult moth emerges completing the life cycle. In our area, there can be two to three generations of webworms per year.
Although the webs are unsightly, defoliation by fall webworms usually cause little harm to mature trees. Most of the energy has been collected and stored by the leaves, and fruit is already set on the trees. Webworms can cause harm to younger trees by completely defoliating them which can lead to low energy stores, nutrient deficiencies, and added stress.
There are several management strategies that can be utilized to get rid of these unwanted pests. The easiest method of control is to prune limbs with webworms from the tree, remove from the site, and burn them. For webs higher in the trees, a telescoping pruning tool works well. Another way to control the webworms is to use a piece of pvc pipe to bust the webs in the trees which exposes them to natural predators such as birds and wasps – let nature do the work for you.
There are also chemical control options. Insecticides containing Bacillus thuringiensis (B.t), acephate, or carbaryl should be applied to the foliage in the webbings or adjacent to the webbing. Hose-end sprayers or high-pressure sprayers are best for reaching upper portions of tall trees. Because webworms remain inside their webbing, sprays must penetrate the web to be effective. Apply pesticides after eggs hatch and before larvae develop dense webs.
Remember that when applying any pesticide, you should read the label and follow all labeling instructions. For those webs in the tops of trees that are out of reach, there is little that can be done.
One common control method that is not recommended is burning the webs while they are still in the tree. Burning can damage the cambium layer of the tree and kill limbs and branches, plus you may catch the tree on fire and have to call the fire department to put the fire out.
Brad Hardison is an Agricultural Extension Agent specializing in horticulture. Contact Brad by calling the Sampson County Extension Center at (910) 592-7161 or by emailing [email protected]