The following article will appear in the October edition of the Piper. Give this is timely information, I thought I would post this here as well...
Grass
Clippings
Brian J. Stiehler, CGCS, MG
October Newsletter
Late summer each year, many trees around the club start
showing ugly masses of webbing on the outer branches. Most confuse these caterpillar nests for tent
worms, when in fact, they are Fall Webworms. Fall Webworms are the larval stage of
an adult moth that is shown below. Tent worms
build similar structures in trees however, they are built in the spring and they
tend to build the webbing closer towards the trunks of the trees.
The adult is mostly white in the North America regions, but
in the south, it may be marked with black or brown spots on the forewings. It is quite 'hairy’, and the
front legs have bright yellow or orange patches. The underwings will have less
marking than the forewings, and the abdomen often has a sprinkling of brown
hairs.
The fall webworm feeds on just about any type of deciduous tree, where leaves are chewed; branches or the entire
tree may become defoliated. In the
eastern U.S., pecan, walnut, American elm, hickory, fruit trees, and some
maples are preferred hosts; in some areas persimmon and sweetgum are also readily
eaten. In the west, alder, willow, cottonwood and fruit trees are commonly used.
According to Scott
Shalaway, who holds a Ph.D. in wildlife ecology from Michigan State
University, Tent
caterpillars eat young vigorous leaves, while webworms eat leaves that have
already done most of their work for the tree. As summer winds down, plant
growth slows, and leaf loss is much less serious than when it occurs in spring
or early summer. Though fall webworms
are never a pretty sight, neither are they particularly troublesome. Web
building begins when the first eggs hatch, usually in early July. Females lay as many as 400 eggs on the leaves
of favorite foods and when the caterpillars hatch, they skeletonize the leaves
and begin building the web. Over the course of four to six weeks, the
caterpillars molt six times and grow to about an inch-and-a-half in length.
Then
they leave the nest, drop to the ground and seek refuge under a rock or a slab
of bark. There they pupate and spend the fall and winter. In late May or June, adults emerge from their
cocoons. After mating, the females lay their eggs, and the adults die. The
adult moth stage lives only a few weeks.
To
protect themselves from hungry birds and other predators, webworms stay
inside their webs and eat the leaves enveloped by the silky shelter. This is
another difference between webworms and tent caterpillars — tent caterpillars
leave their tents to eat fresh leafy growth.
If it sometimes seems that
evidence of fall webworms appears overnight, that may be the case. Webworms, which are recognized by long white
or pale-yellow hairs on each body segment, work all night long and after the
colony grows to a certain size, the web grows quickly. A large nest may be
three or four feet long and encase several branches.
For
those who wish to control webworms, there are several options. A popular,
though dangerous, treatment is to burn webworm nests. I discourage this choice
because it can be very dangerous for trees and humans. Preferably, open webs with a stick to give
predators such as cuckoos, orioles, tanagers and vireos access to the
caterpillars. These birds are among the few that eat hairy caterpillars. Chemical treatment with insecticides is also
possible, but I don’t recommend it.
Webworms
are most active late in the season, so the damage they inflict is mostly
cosmetic. Defoliation of at least 20 percent of a tree’s leaves are necessary
before plant health declines. If you
just have a few webs, simply prune the tented branches and destroy them.
Because webworms usually don’t cause permanent damage, I recommend a
laissez-faire approach.