–by Raymond Cloyd – Horticultural Entomologist
Damage caused by mimosa webworm, Homadaula anisocentra, larvae/caterpillars is prevalent on honey locust, Gleditsia triacanthos, and mimosa, Albizia julibrissin, trees throughout most regions of Kansas. The larvae/caterpillars are 1/2 of an inch long when full-grown (Figure 1)
Figure 1. Mimosa webworm caterpillars feeding on leaves (Raymond Cloyd, KSU)
and rapidly move backward when disturbed. Caterpillars’ web leaves together on the ends of branches (Figure 2).
Figure 2. Mimosa webworm webbing on end of branch (Raymond Cloyd, KSU)
Webbing typically starts at the tops of trees and protects caterpillars from natural enemies (parasitoids and predators) and insecticide spray applications. Heavily-infested trees are brown or scorched in appearance (Figures 3 through 5) as the caterpillars skeletonize the leaf tissue. Caterpillars eventually fall from trees on a silken strand before pupating. Mimosa webworm pupates in bark crevices or pupae are attached to structures (e.g. buildings). There are two generations per year in Kansas.
Figure 3. Mimosa webworm caterpillar feeding damage (Raymond Cloyd, KSU)
Figure 4. Extensive feeding damage caused by mimosa webworm caterpillars (Raymond Cloyd, KSU)
Figure 5. Extensive feeding damage caused by mimosa webworm caterpillars (Raymond Cloyd, KSU)
At this time of year it is too late to apply an insecticide when trees are already heavily infested with webbing because caterpillars are protected from insecticide spray applications inside the leaf webbing. However, next year, you can manage mimosa webworm caterpillar populations by applying an insecticide when the caterpillars are initially present and exposed to insecticide spray applications. You can use insecticides that contain the following active ingredients: Bacillus thuringiensis subsp. kurstaki, spinosad, bifenthrin, cyfluthrin, and permethrin. Read the label of each product to ensure that “webworms” are listed. High-volume spray applications are required to contact the caterpillars. If possible, selective pruning can quickly remove isolated or localized infestations of mimosa webworm.