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Fall defoliators As we enter mid-August, we usually
don't think of fall, at least not quite yet. One reason we call
fall defoliators exactly that is that the growing season is late
in the second half. Some of the names of the defoliators also
have fall in their name.
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 mid-August 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 (read
caterpillar) 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 Bt products such as
Thuricide. Other control options include the standbys such as
Sevin, permethrin, Othene, malathion and others.
The way that insects live also dictates some of the control
dos 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 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.
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 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 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 wingspans of at least 4 inches.
In summary, control of fall defoliators usually isn't justified
from the plant's standpoint. Forested areas have heavy pressure from
this group of 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.
[John
Fulton, unit leader,
University of Illinois Extension,
Logan County Unit]
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