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, diazinon, 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.
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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 4 inches.
In summary, control of fall defoliators isn't usually 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.
With the excessive heat, the cycle of these insects will be sped
along. We can probably figure two to three weeks early for many of
them this year.
[Text from file received from
Fulton, University of Illinois Extension,
Logan County Unit]