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John Fulton


John Fulton
Former County Extension Director



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In The Backyard

Horticulture columns and tips done on a timely basis

Fall Defoliators

Posted by John Fulton -

Much damage has already been done to trees by diseases and insects. Fall traditionally brings more insects intent on devouring the leaves remaining. Let's begin by listing some of the culprits. Fall webworms, Eastern tent caterpillars, Tussock moth larvae, Walnut caterpillars, Cecropia moth larvae, and a host of others are all considered fall defoliators. What is defoliation? It is simply removing the leaves from a plant. This group of insects accomplishes the feat by eating leaves.

What does fall defoliation do to a tree or shrub? It does two things. First it removes the leaf tissue so that less food is made for the plant. Second, the insects, their webs, or their damage can be unsightly. In the end, damage happening to a tree or shrub in September is usually cosmetic, unless you have new transplants or plants that aren't healthy to begin with.

Most fall defoliators come to us as the larval stage (caterpillars) of a moth. When we talk about controls of the larvae, the fact that they are larvae of moths or butterflies makes them susceptible to the use of B.t. products such as Thuricide. Other control options include the standbys such as Sevin, diazinon, Othene, malathion, and others.

The way that insects live also dictates some of the control do's and don'ts. Fall webworms live inside a "web" all the time. They actually expand the webbing as they need to have more leaves to eat. They are usually worst on fruit and nut trees. You can even clip the nest (and the branch it is around) off the tree and burn it. I guess this tells you that defoliation caused by the insect isn't that great of a threat to the tree or you wouldn't cut the branch area off. If you want to spray fall webworms, you need to get the spray through the web. This may be a little harder than you think. If you don't have enough pressure, the spray just runs off the webbing.

In the case of Eastern tent caterpillars, they hatch out of a common nest. They then leave the nest to feed, but generally return in the evening to congregate in the area of the nest. They are not covered by webbing, and the time they are congregated is a great time to spray since they are usually in one area on the trunk or main branches of trees.

Of the other fall defoliators mentioned, the giant Cecropia moth larvae are quite a sight. If you are able to see one. They are very large caterpillars that can eat tremendous amounts of leaves in a hurry. There are other related moth larvae such as Prometheus moths, but they are all in the giant silk moth family and the moths usually have wing spans of at least four inches.

In summary, control of fall defoliators isn't usually justified from the plant's standpoint. Forested areas have heavy pressure from this group in insects every year, and the trees are still thriving. The exception is newly transplanted or struggling plants. If appearances are important, consider a control spray.



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