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Webworms on Honeylocust

Watch for brown leaf tips with webs

By: Sandy Feather ©2010
Penn State Extension


Q. My honeylocust tree has webs all over it. When I look closely, I can see these little worms in the webs. What are they and what can I do about them? My tree looks like it is dying!

A. The writer included photos of the problem. It appears to be an infestation of mimosa webworm (Homadaula anisocentra). While this insect is a pest of mimosa (Albizia julibrissin), it is actually a more common pest of honeylocust (Gleditsia triacanthos var. inermis) in our area. I have seen a number of reports that suggest ‘Sunburst’ may be more susceptible to mimosa webworm damage than other cultivars, but all honeylocusts are subject to attack.
    

webworms on honeylocust

Mimosa webworms overwinter as pupae protected in cocoons. They can be found under the scaly plates of bark found on honeylocusts, or in fallen leaves under the tree.

 


Life Cycle of Webworms

Silvery gray adult moths hatch out in June and lay eggs on flowers and foliage of host trees. The eggs generally hatch in mid- to late June. The larvae web leaflets together and feed on the foliage protected by the web. The larvae usually feed in large groups, and enlarge the nest as needed to encompass more foliage for food. I have seen entire trees enmeshed by these webs. A second generation hatches out in August. If you control the first generation successfully, the second should cause little damage.

webworms on leaves


Tree Care

Prune out and destroy small infestations within easy reach. If a large percentage of the tree is affected, that is not practical. Since mimosa webworms are moths, Bacillus thuringiensis (Bt) provides excellent control of small larvae. Once they grow to a larger size, over one-half inch, Bt will not be as effective. Other insecticides labeled to control mimosa webworm include BioNeem (azadirachtin); Sevin (carbaryl); Bayer PowerForce Multi-Insect Killer (cyfluthrin); pyrethrins and piperonyl butoxide; and Captain Jack’s Deadbug Brew (spinosad).


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