Question: I see large holes in the trunk of my cottonwood tree, but I’ve seen no insects in them. There is sawdust coming out of the holes. What threat does that pose to the tree?
Answer: A very great threat. That’s damage of cottonwood borers, nemesis of willows as well. They’re the larval form of the large black and white beetle with long antennae extending back over its back. You might use a borer preventive spray on 6-week intervals in the growing season, but that’s a lot of work for unpredictable results. If you ever notice a mature cottonwood that is really sparse and lethargic, that’s probably the accumulated damage of this insect pest. Trees like that need to be removed before they fall and damage property and hurt people and pets.