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 What happens is a fine mist of sap coats things beneath a tree.
This is actually called “honeydew,” which is a secretion of
sucking insects such as aphids and lace bugs. There are
different species of lace bugs for most plants. The same can go
for many species of aphids. What makes matters worse is a fungus
begins growing in the honeydew, making it turn black.
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 weather we have experienced has increased aphid
numbers at a very great rate. Many of the natural controls, such
as lady bugs and syrphid flies are also evident of a large
number of aphids.
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.
Fall Defoliators
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 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 defoliators.
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 is 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 B.t. products such as
Thuricide. Other control options include the standbys such as
Sevin, Othene, malathion, bifenthrin, permethrin, and others.
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Fall Webworm
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.
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.
[By JOHN FULTON, COUNTY EXTENSION
DIRECTOR SERVING LOGAN, MENARD, AND SANGAMON COUNTIES]
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