Fall Webworm, No. 20

Hyphantria cunea
Order: Lepidoptera
Family: Arctiidae

Fall webworm webs are a common sight in pecan trees throughout Mississippi, but they are especially common in the southern portion of the state. Although these caterpillars will feed on many other hardwood trees, pecan and persimmon are by far their most preferred species here. Caterpillars feed inside a communal web, which protects them from birds as well as insect predators and spiders. As caterpillars grow larger, they will venture outside the web at night to feed on nearby leaves. Fall webworms are present every year, but populations are heavier some years than others. During heavy outbreak years they can completely defoliate large pecan trees. Such severe defoliation adversely affects nut fill on the current year’s pecan crop and reduces yield potential for the following year. Commercial pecan producers can easily control webworms by spraying appropriate insecticides with high volume air blast sprayers, but it is seldom safe or practical to apply foliar sprays to large trees in home and urban settings. Fortunately, although the webs are unsightly, mature hardwood trees are able to survive heavy, or even complete, defoliation without suffering long-term adverse effects, other than to nut production.

Control:  Doing nothing is the most common, and usually the most practical approach to dealing with fall webworms on large landscape trees. One mechanical control method that is somewhat helpful is to use a hook fastened to a long pole to tear the webs apart, thus exposing the caterpillars to mortality by predation. Trees that are still small enough to be safely and properly sprayed with some type of hand-held sprayer, or a “tree-and-shrub” hose-end sprayer can be sprayed with spinosad (Fertilome, Bonide, Monterey, and Greenlight sell products containing spinosad), taking care to get good coverage of the web, as well as nearby leaves. See the fall webworm section of MSU-ES Publication 2369, Insect Pests of Ornamental Plants in the Home Landscape, as well as the section on “Insecticides in the Home Landscape, for more information.