Is it forest tent caterpillar?
The webs or tents being seen on trees in northern Minnesota are causing a lot of confusion. Lots of people are asking is it forest tent caterpillar, ugly nest caterpillar, fall webworm or what? Of course none of you, loyal and faithful readers of the newsletter, were confused were you. When you saw the tents you just referred to the feature article in the last issue of the Newsletter titled " Webworms, tent caterpillars and other web- making insects"and you were able to immediately determine that the tents were made by the fall webworm.
As you know, the tents that are obvious across northern Minnesota on alder, hazel, willow, oak, aspen, birch, etc. were made by the fall webworm. But did you know that fall webworm was introduced into Europe and Asia from America. Unfortunately, "Introducing" pests works both ways.
Fall webworms are unlikely to kill trees. Outbreaks only last for two to three years and most feeding damage is confined to the tents or webs. No controls are usually necessary. Braconid and ichneumonid wasps are effective natural controls but usually do not build up until webworms are quite abundant. If their presence bothers you for aesthetic reasons or the web is on a young sapling, you might want to try some of these ideas. On small trees and shrubs the best control is to clip off the branch with the tent and dispose of it or burn it. Do not burn the tent while it is still on the tree. This usually kills the branch replacing an ugly tent with an ugly dead branch. Insecticides (Bt, malathion or carbaryl) can also be used but have to be applied with enough pressure to penetrate the web or the web has to be torn open to get the insecticide inside. Destroying the webs with a household broom might be the most efficient method of "cleaning house".