For many years, there didn’t seem to be a need to spray our maples and oaks with dormant oil. In the last few years, many of you have seen a small green caterpillar that has attacked our oaks and maple trees. You will have seen them on many of your flowering trees, as well. This caterpillar is from the winter moth.
If you think back to November into early December, you probably saw a lot of moths flying around the outside of your home. This was the male winter moth, and he was looking for the female winter moth. The females tend to gather on the trunks and lower branches of trees. After the moths mate, the females lay eggs on the trunks and branches of the trees. The moths then die, and the eggs wait for warming temperatures before they hatch.
The tiny caterpillars will, early on, attack the flower buds of fruit and ornamental flowering trees. They can kill the flower buds and dramatically decrease the amount of fruit produced on fruit trees. They can do major damage to the foliage of trees. In many cases, they can cause major damage to the new leaves of maples, oaks, ornamental flowering trees and even some shrubs.
It has been shown that several years of this early-in-the-season damage to leaves can lead to the death of branches or even the death of the trees. For this reason, the eggs should be controlled by an application of dormant oil to the trunk and the lower branches of your oak, maple and ornamental flowering trees.
The oil spray will kill many of the eggs and thus decrease the number of caterpillars that feed on your trees. You may have to follow up with an insecticide once the leaves begin to open. However, it is a lot easier to kill the eggs now than it will be to control those caterpillars that are all over the tree.