Worms, webs and bags, oh my — What’s in my trees?
- col-gary-graham
- September 28, 2022
- 539
Although there’s lots to love about fall, one of the things nobody loves are some tree pests that cause homeowners a great deal of unrest.
If you have been in Ohio for more than a year, you have no doubt seen the two “cardiac pests of trees” — bagworms and fall webworms, two completely different critters that strike both anger and fear into many a landowner. With these recent calls to my office, I already know the question is “How do I kill or get rid of these things?”
Similarities
Both pests can cause severe defoliation to the trees and leave trees either in poor health or with unsightly damage. By the time you see the little brown cocoon bags or the big white webs up in the tree, the best treatment timing has already passed. You can apply chemicals, but it is a waste of money and effort — both are issues you want to start treating earlier in the spring. Both pests cycle and will have a larger infestation every so many years. The good thing is that the higher populations are good for the predators who eat them.
Treatment
Bagworms are typically found on arborvitae, junipers, and other trees in the conifer family like spruce, pine, willow, and locust trees, apparent when you see the defoliation or the little cocoon-type bags hanging in the trees. Inside the bag is a silk-shaped spindle that is covered with conifer needles, foliage or other debris from the area. Inside the bag is a female bagworm that can produce over 1,000 offspring. Once the bags are formed, chemicals can no longer penetrate and kill the pest. In the spring, they feed on buds and young foliage, causing areas to die back. If excessive enough in numbers, they can cause enough defoliation to weaken the tree and potentially kill it.
If you had a large infestation in the fall, start by pulling as many of the bags off of the tree as you can safely reach, then burn them. Do not leave them lay under the tree, as the female can still emerge and lay her 1,000 offspring. At a 1,000 offspring per female, it is easy to see why the population can explode over a couple years. After removing bags in the fall, the next spring, you can apply BT spray. Another chemical option is an insecticide containing the active ingredient of pyrethroids. The challenge to using chemical approach has two parts:
Part one and the hardest one is you really have to have complete coverage of the entire tree and surrounding trees to do any good at getting ahead of the infestation. If you have conifer trees taller than 10-15 feet you probably don’t have a practical or safe way to apply product higher than this and may need to hire an arborist to do it.
Part two is application timing when the majority of young larva are out feeding. Inspect the trees several times during the day. Early morning and late evening you may find them feeding on the top to the limbs and needles. When the sun is out, you will have to look under the limbs and needles as they retreat to the shade and cooler parts of the tree. Oftentimes these half-inch long larva will have needles affixed to their bodies as camouflage from predators.
It may take several years of spraying to get a huge infestation under control. If you treat and your neighbors do not you still could end up with them, as the larva will use a silk string in heavy winds to float to trees close by.
Fall webworms are much different than bagworms — they are found in deciduous trees and only noticed in the fall from their large white webs, and by the time the webs are visible, they have been here awhile and are on their second generation of the year. Here is the important thing to remember about fall webworms: Neither generation does significant damage to the tree other than the unsightly webs. Webworms are a good source of food for predators of insects.
As early as May and into July, female moths emerge from cocoons in the soil or leaf litter to lay eggs on branch tips. This is typically done higher in the trees. The first-generation nests are seldom as numerous or as large in size as those produced by the second generation. First-generation nests normally involve only a few leaves. Second generation female moths, however, often lay their eggs on or near the nests from which they developed, thus second-generation caterpillars expand the nests once occupied by first-generation caterpillars.
The second generation nests in Ohio typically reach their maximum size in the fall, which accounts for the common name. The fall webworm is not usually a serious pest in woodland forest stands, but infestations are of greatest concern to homeowners on shade, ornamental, and landscape trees. Here, loss of foliage and unsightly webs seriously reduce the aesthetics of the trees in the yard, so control of the fall webworm may be desirable.
Just as with bagworm, control measures should be initiated when the webs and the larvae are small in early summer. Smaller larvae are also easier to kill. Large webs make it difficult for insecticides to penetrate and contact the larvae within.
Total coverage to get the first-generation webs means you need total coverage of the tree. Hire it done if it bothers you that much — don’t get hurt trying to stop a pest that is unsightly, but not really causing major damage. For effective control spray the web and the foliage surrounding the web. Many insecticides (such as Sevin, BT, or Malathion, etc.) may be used. Hand eradication is also possible when smaller webs are spotted early. In young trees that can be safely reached, prune to remove the webs.
When I was a kid, fall brought on the yearly tradition of my dad burning the webs out. However, we now know that burning webs out of trees with fire usually does more damage to the tree than the damage caused by the webworm. So, never burn fall webworms out of a tree.