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BY DON MEEHAN
CATERPILLAR DAMAGE TO CONIFERS
Spring is the time of the year when it becomes very evident that we might be having an invasion of tent caterpillars on conifer trees and shrubs. For example, a trip through the landscape will often reveal caterpillars one half inch to one inch long consuming Douglas fir, pines and spruce trees. The first reaction to this sort of find is that another tent caterpillar invasion has begun. If you remember, only a couple of years ago we did have a major tent caterpillar invasion which did severe damage to acres and acres of trees.
Finding what appears to be tent caterpillars, half inch or longer, at this time of the year would be an incorrect diagnosis. What you would have most likely found is the caterpillar (larval stage) of the Silver Spotted Tiger Moth. It is worth pointing out that it is possible to find tent caterpillars also at the time of the year since in past years I have seen them emerge from their egg cases the first week in March. However, they would be very small in size, probably about one quarter of an inch long at best, AND they would NOT be found on conifer species.
The Silver Spotted Tiger Moth is a common insect in Island County and the Puget Sound region. It is not considered a serious pest since the damage they do is not devastating to trees. They get confused with the tent caterpillar because both produce tents. Unlike tent caterpillars, the Silver Spotted Tiger Moth will have somewhat lengthy tufts of black, reddish-brown, and yellowish hairs on the larval stage. Their life cycles are quite different also. Silver Spotted Tiger Moth larvae will pupate to become an adult moth around the end of June. Laying by the emerging adult moths takes place midsummer. The eggs are laid on needles and twigs of host plants (conifer) in small clusters. Within two weeks the eggs will hatch and newly emerging larvae will begin feeding on the host plant. Obviously, these larvae are very small and most often go unobserved.
Feeding will continue into the fall when the weather slows down activity. Nests, rather tents, will be very small at this time and hardly noticeable. On warm days, during the winter, feeding will resume.
Damage from this fellow is limited to the loss of needles, often on whole branches. As they mature in the late winter and early spring they often leave the "home" branch and venture forth feeding on other parts of the tree. One good aspect of their damage is that they do not eat the buds on the twigs, allowing for new needles to come forth later in the summer.
There are several strategies of control for these insects. The most obvious is Do Nothing. This option works wonderfully if the tree has little ornamental value in your landscape. Or the tree is very tall with the infestation out of reach and normal line of sight. Another option is to discover the problem early in the year, February or even January, and clip out the infested branch. This early in the year will mean very little damage done to the tree or shrub by the pruning out process. Later in the year this approach will have to be weighed with the aesthetic damage possible. The third option includes spraying. There is one excellent material all people should have in their bag of tricks for dealing with caterpillars of most kinds, that material is BT (Bacillus Thuringiensis). It is particularly safe to use for the user as well as the environment. Other spray materials are registered, including several common home and garden insecticides. Consult with our office for names of these materials, but be prepared to be talked out of using them on this particular pest.
We do have a publication available on the Silver Spotted Tiger Moth that covers, in a bit more detail, the things I have addressed already. It costs 25 cents.
LOOKING TO PUT IN SOME NEW PLANTINGS? ARE THEY DROUGHT HARDY?
This is the time of the year a lot of landscaping begins to happen. New plants are being added, old landscapes are being revised, the dead and dying are being removed and replaced. One of the things I would hope you do in this process is to evaluate the kinds of plants you are putting in for their level of drought hardiness. Most of our native plant materials have considerable drought hardiness. Putting in this type of plant will save WATER, money, PESTICIDES, labor. We have a list of Native plants we can share and another on drought hardy plants for the Puget Sound region. Call and we'll mail you a copy of either. By the way, have you organized your landscape so that plants needing the most water are clustered together and those needing less are too? This can make a big difference in the way you manage your yard irrigation.
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