Eastern Tent Caterpillars are here now

Anyone who grows anything knows the growing season started late this year.

Last year started out so different with the early warm spring, but a mid-spring frost killed the flower buds on lilacs and other early bloomers.  Mosquitoes are definitely here now thanks to all the wet weather we’ve been having, if not a bit later than usual.  Another insect that has arrived is the eastern tent caterpillar.  By the time this article comes out I’m sure they will be in our area.  Jeff Hahn, assistant extension entomologist, claims they will be in the Twin City area by the end of May.  What we don’t know is how many will show up.

The caterpillars are bluish black with a yellow and white stripe running the length of the top of their bodies.  They are also mostly smooth, except for a series of hairs sticking out along the sides of their bodies.  They are two inches long when fully grown.

However, the first sign you’ll notice are the silken tents they create in the forks of branches.  After the caterpillars first hatch, they’ll construct this webbing, which serves as a shelter they use at night and during rainy weather.  The tent will be small at first, but will increase in size and can eventually become quite conspicuous.  During the day they crawl out of these tents and feed on tree leaves.  Although they are found on a variety of hardwood trees, eastern tent caterpillars are particularly fond of fruit trees including apple, chokecherry, crabapple, plum and cherry.

Also consider the size of the caterpillars.  As long as they are no more than half their full-grown size, i.e. one inch or less, it is worth considering whether to treat them with an insecticide.  This is not an issue now, as they are just emerging and they are all small.  However, if an infestation is discovered later, it is important to check to make sure they are not too large (larger than an inch).  The larger they are, the closer they are to being done feeding and then it is not worthwhile to treat them.

A great non-chemical method to deal with eastern tent caterpillars is to wait until they have retreated back to their webbing at the end of the day or on a rainy day and then pull out the webbing, along with the caterpillars.  Then bury or bag them to properly dispose of them (you could burn them if it is permitted where you live.)

There are a variety of residual insecticides that you can use if it is desirable to protect your trees.  Consider using products that have a low impact on the environment, such as Bacillus thuringiensis, spinosad and insecticidal soap.  Bacillus thuringiensis is a particularly good product if the tree is flowering since it will not harm honeybees.  If you use insecticidal soap, the product needs to make direct contact with the insect.  There is no residual activity, so you may need to repeat the treatment.


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