Purdue University Extension has an excellent factsheet on mimosa webworm that contains more information about treatment options.Īt this point, it is probably best to just keep your honeylocust healthy by watering them through this hot and dry summer, mulching properly and scouting for webworm cocoons (small white puffed rice-shaped) at the base of trees and on the trunks, and prepare to manage them next year if necessary. Other biorational pesticides such as spinosad (Conserve), azadirachtin, and chlorantraniliprol (Acelepryn) can also be used to treat mimosa webworm. The webworms are caterpillars, in the Lepidoptera order of insects, and can be treated with organically registered pesticides that contain Bacillus thuringiensis (Bt), a naturally occurring bacterium that kills caterpillars and is non-toxic to mammals (humans). Honeylocust trees can be treated for mimosa webworm if they are discovered early enough (mid-June), before the leaves are brown and webs formed in August. The webs and browned foliage are unsightly, but the damage is more aesthetic than serious. Healthy trees have already set buds for next year and losing foliage a month before the leaves naturally fall off is not a major health issue for the trees. Mimosa webworm, like fall webworm found on hickories and other native trees, is a late season defoliator, that typically does not cause major harm for honeylocust. How much harm are these caterpillars causing?.The cocoons are white and look like puffed rice. A second-generation caterpillar leaves the tree canopy to find a site where it can spend the winter in a cocoon protected from cold temperatures. They have a dark head, and the body is sometimes tinged with pink. Fully grown caterpillars are about 1 inch long and grayish brown in color with five lime green stripes running down the body. Mimosa webworm are small caterpillars that spin their cocoons between the folded leaves that they have webbed together. Mimosa webworms are typically found in southern states, but they are surviving our more recent warmer winters, especially in urban areas which tend to be warmer. The mild winter temperatures this year have led to a large outbreak of mimosa webworm on thorn-less honeylocust that are planted as street, park, and landscape trees throughout Pennsylvania. It is mid-August and many honeylocust trees (young and old) are covered in brown leaves that are matted together with webs at the tips of branches.
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