By Dr. Raymond Cloyd, Professor and Extension Specialist
Mimosa webworm, Homadaula anisocentra, larvae or caterpillars are causing noticeable damage to honey locust, Gleditsia triacanthos, and mimosa, Albizia julibrissin, trees throughout Kansas.
The caterpillars are 1/2 of an inch (12.7 millimeters) long when full grown (Figure 1) and move backward rapidly when disturbed. The caterpillars web leaves together on the ends of branches (Figure 2).
Caterpillars create webs near the tops of trees, which protects them from natural enemies (parasitoids and predators) and insecticide spray applications. Trees heavily infested with mimosa webworm are brown or scorched in appearance (Figure 3).
The caterpillars eventually depart from trees using a silken strand before pupating. Mimosa webworm pupates in bark crevices or the pupae are attached to structures (e.g. buildings). There are two generations per year in Kansas.
It is too late to apply an insecticide this time of year when trees are heavily infested with webbing because the caterpillars are protected from insecticide spray applications inside the leaf webbing. However, next year, you can manage mimosa webworm caterpillars 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. Bacillus thuringiensis subsp. kurstaki and spinosad are stomach poisons so mimosa webworm caterpillars must ingest the spray solution on the leaf surface in order to be killed. High volume spray applications should be used so that the insecticide contacts the caterpillars or there are residues on the leaf surface. If feasible, selective pruning quickly removes isolated or localized mimosa webworm infestations.
