Fall webworm populations explode
While driving through Springfield the other day, I glanced over at a row of trees and wondered why it looked like so many were dead. Figuring they were ash trees, I didn’t pay much attention.
However, I came upon another batch of trees that looked the same and became interested; what was going on? Upon closer inspection, I was quite shocked to see the trees heavily covered in fall webworm nests.
There were so many fall webworm nests on the tree that they appeared gray and dead.
I was shocked because in all my many years of horticulture, I can honestly say that I have NEVER seen populations of the fall webworm caterpillar this large.
Fall webworm, despite the name, hatches in late June. The name refers to when people tend to start seeing the nests due to their size.
The caterpillar overwinters as eggs on the tree. They hatch in June and begin to construct their nests. This is the first generation of fall webworms. Their nests are not that noticeable unless you know what you are looking for.
The second generation is what we see now. These caterpillars are feeding on the foliage inside the nests.
People sometimes confuse fall webworm with Eastern tent caterpillars, which hatch in early April. ETCS build their protective nests in the branch crotches of trees. They venture out of the nest to feed on foliage during the day.
Fall webworms build their nests around the ends of the branches, surrounding the foliage upon which they feed. As they mature, they continue to expand nests around additional foliage.
ETC tends to prefer trees in the rose family such as cherry, crabapple and those in the prunus genus. They will feed on a wide variety of plants.
Fall webworm really likes walnuts and those plants in the genus juglans (hickory, pecan). Most of the trees that were heavily covered were walnut trees along the bike path.
There are two very important things to think about when it comes to these caterpillars. First, they won’t likely kill a tree. Their nests and feeding tend to be more of an aesthetic problem.
Second, spraying pesticides on their nests will not kill them. These nests are protective and prevent penetration of sprays. The best control is removing the nests and caterpillars by hand.
If you have a small tree that has either of these caterpillars, you can easily remove them by hand. A smaller tree that is defoliated year after year may suffer, so it’s a good idea to eliminate the caterpillars if possible.
It will be interesting to see what happens next season. These caterpillars may fall prey to predators or biological controls such as a disease-causing pathogen. I will be keeping my eye on these trees in Springfield to see what happens next year.
What are you seeing in your area of the Miami Valley? Send me an email with your comments and I’ll try to summarize them in a future column.