Spider-Looking Webs in Your Trees

Blake Layton: Farm and Family is a production of the Mississippi State University Extension Service.

Today we're talking about spider-looking webs in your trees. Hello. I'm Amy Myers, and welcome to Farm and Family. Today we're speaking with Dr. Blake Layton, Mississippi State University Extension entomologist. Dr Layton, it looks like I have spider-looking webs or like this pantyhose mass growing in my trees. What might this be?

Blake Layton: Well Amy, this is almost surely at this time of the year the webs of fall webworm. So this is a caterpillar pest that's really common at this time of the year. These webworms, that's a communal web that may contain several hundred caterpillars, all feeding inside that web that they've helped produce to provide them protection from birds, and parasites, and predators.

Amy Myers: Okay, so that's why it's called webworm, because it looks like spider webs, or even pantyhose has also been a description of it. So when should I start looking out for them? What do we look for when we're looking out for these little critters?

Blake Layton: Well, these are called fall webworms because they are by far more numerous in the fall, but we can start seeing the first webs in May or June. They have several generations a year, two or three. That first generation is usually not that numerous. It'll be something you notice and if you have a small tree that happens to have a web in it, well, it may be significant for that small tree, but once we get into the fall, that's when those numbers can really increase.

Amy Myers: And the moth looks like a little white moth first?

Blake Layton: The moth, you rarely see the moth, but when you do see them, they're about maybe three quarters of an inch long, and the female moths at least, their wings are pure white. They lay a layer of eggs on the leaves. There might be 300 to a thousand eggs in that quote "cluster", and they're kind of lime green, but we rarely see those, because they're up in the tree canopy.

Amy Myers: So you really don't see them until they're up in the tree and making webs.

Blake Layton: That's right. That's usually your first clue that you've got fall webworms, when you see those little small webs begin to grow. The small caterpillars start building them, and as they grow larger they build the web a little larger.

Amy Myers: What kind of damage do they cause to trees and what kinds of trees do they infest?

Blake Layton: Here in Mississippi we primarily see them on pecan, and persimmon, and sometimes a few other species, sometimes on sweet gum. In outbreak years, like we're having this year, their populations are really cyclic and so we may go some years where yeah, you see a few but it's no big deal. Then we have a year like we're having now where it seems like they're everywhere, and in outbreak years they'll occur on a lot of other hardwood trees. And I've even had some reports this year of them occurring on bald cypress, which is a little unusual.

Amy Myers: So do they kill the trees or hurt the trees?

Blake Layton: Actually they're pretty harmless to the tree. The big damage, at least in home lawns and ornamental trees is that short term aesthetic impact and that does bother a lot of people. Now they can be a significant pest in commercial pecans, but fortunately commercial pecan growers have these air blast sprayers that can spray 50 feet up in the tree. They don't have any trouble controlling these things. It's a little bit different story for homeowners in an urban setting.

Amy Myers: So how do we get rid of these or treat them?

Blake Layton: They're pretty difficult to treat in an urban setting just because it's not really possible to spray a big tree without having drift maybe over into your neighbor's yard, your neighbor's swimming pool, vegetable garden, all those issues.

One of the things I can recommend that helps a little is to maybe take a fishing pole, tape a clothes hanger on the end in the form of a hook, and you can use that for those webs that you can reach to pull those and tear them apart. One thing people like to try to do is do the same thing with something that they can light fire to and burn those webs out, but that's going the wrong way, because that fire will do permanent damage to the tree, whereas the few leaves that those webworms have eaten, that's a short term effect.

So there are insecticide treatments that can be used to protect small trees and that can be very useful. So we have several insecticide sprays usually containing the active ingredient Spinosad is the one that I recommend. There's a lot of commercial formulations out there that you can buy at your lawn and garden center. That's a useful for small trees, say 20 feet tall or shorter, that you can reach with that insecticide.

Amy Myers: Okay, so don't burn your tree down, but you can spray with that insecticide or drag off the masses with a hook or a fishing pole or whatever. Okay, so for more information, do we go to extension.msstate.edu and then in the search box type in webworm for more information?

Blake Layton: That should work. If you do that, you should find at least two newsletter articles that we have there about these fall webworm.

Amy Myers: Today we've been speaking with Dr. Blake Layton, entomologist. I'm Amy Myers and this has been Farm and Family Have a great day.

Blake Layton: Farm and Family is a production of the Mississippi State University Extension Service.