What is wrong with my Chestnut Crabapple tree?
Our young Chestnut Crabapple has been hit by two things at once. At the base, the trunk looks and feels rotted out when you scratch it a bit as if a fungus or borer has gotten in and is damaging it. And up in the foliage, I noticed one or two of the leaves are curling and turning limp and brown. What could these problems be and what can we do? The tree gets good sun most of the day and was planted with about one foot of light gravel (diameter) around it at the base to discourage weeds and rodents.
Katherine Garland, Horticulturist
Unfortunately, I suspect you’re dealing with borers. It’s tough to say for certain without physically inspecting the tree, but the torn up trunk and sawdust are both indicators that your tree has had a significant amount of borer activity. Borers are quite common on young apple and crabapple trees. While one or two borer holes won’t bring a tree down, this level of damage does not give me much hope for your tree in the long-term. Here’s more information about borers in the future from our Growing Fruit Trees in Maine website.
“Roundheaded apple tree borers lay their eggs on the lower trunk usually near the ground, from late June into August. Upon hatching, the larvae burrow into the lower trunk. The tunneling can kill the tree by structural damage to water conducting tissues and in severe cases will cause the trunk to break off completely. Small pinholes with reddish frass indicate the presence of boring larvae. Pencil-sized holes in the trunk indicate that the borer has done extensive damage and has already left the trunk. Flatheaded apple tree borers feed primarily on the sapwood of trunks and larger branches on trees with poor growth, and trees with damaged bark. The dogwood borer, which feeds near the surface of the trunk, is less devastating.
Fruit trees sprayed with foliar insecticides during June, July and August are much less likely to be attacked by trunk borers. For trees not receiving foliar insecticide sprays, insecticide application to the trunk at two-week intervals from late June to mid-August will reduce the likelihood of borer attack.
To prevent borers from laying eggs, a loose-fitting barrier such as mosquito netting or window screen can be wrapped around the lower trunk and closed at the top by tying it with a cord and closed at the bottom by mounding soil over it. Barriers should be in place by the end of June, but loosened or removed after harvest to prevent girdling. When a cord or trunk guard girdles a tree, it kills the tree and defeats the purpose of the trunk guard.”
There is a possibility that it could be necria (photos of the disease and more info) or a combination of necria and borer damage. No matter what, the soft trunk is a sign the plant will not ever fully recover.