NDSU Extension Service - Burleigh County


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Fall Webworm

Are you starting to see caterpillar nests in your trees? Fall webworm is starting to become active this time of the year. You will find these caterpillar nests in various trees such as chokecherry, birch, and elm trees. Don’t worry you won’t have to prune the branches with the nest out or try to torch the pests.

Pruning or torching causes more damage to the tree than the pests.

Though these nests can appear to be destructive, the caterpillars actually do little harm to the trees.  The caterpillars are eating on the leaves, but our leaves are mostly done for this year resulting in the minimal damage.  A person can simply break up the nest with jet spray of water or the end of a broom hand to the get rid of the caterpillars.
Webworm Photo Credit:  James B. Hanson, USDA Forest Service, Bugwood.org  (http://www.insectimages.org/browse/detail.cfm?imgnum=0949060#collapseseven)

Insecticides are available if you want to just kill the caterpillars all together.  Carbaryl and pyrethrin are widely available and will have an immediate kill on the pests.  A person can use a safer group of insecticides as well, but it will take a couple days or longer before the caterpillars die.  This group includes: Bacillus thuringiensis, neem, and spinosad.  These insecticides are most effective to use when the nest first appears.

Photo Credit: James B. Hanson, USDA Forest Service,   Bugwood.org

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