There are two ways to deal with the problem. The first way is to
spray the entire tree with a product such as malathion,
bifenthrin or permethrin to kill the insects. The second way is
to move anything portable from under the tree. If you opt for
the first option, you need to make sure you can spray the entire
tree. The kind of weather predicted will increase aphid numbers
at a very great rate.
The end effect on the tree isn't all
that great as long as adequate moisture is available. This means
a shot of water when it stays dry for a week or more. We'll also
be coming up on lawn fertilization time in about a month, so
that fertilizer will help the trees as well.
As we enter August, we usually don't think of fall -- at
least not quite yet. However, a quick trip through southern
Illinois this weekend showed that the heat of the season has
caused insects to develop faster than usual. The fall webworms
are out in force, and they are one of the more visible fall
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
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, Othene, malathion, bifenthrin, permethrin and others.
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The way the insects live also dictates some of the control dos
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.
In the case of eastern tent caterpillars, they hatch out of a
common nest. They then leave the nest to feed, but they 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.
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.
We're at the fair
Logan County Fair week is coming up. We'll be hard to reach
because of the various 4-H shows. If you really need to speak with
someone in the office, you can always call the office at 732-8289.
You may have to leave a message on the answering machine, but we'll
get back to you as we are able.
University of Illinois Extension, Logan County]