Japanese Maple – Asian Ambrosia Beetle toothpicks
Q: My Japanese maple appears to have fallen victim to some sort of attack. Some of the limbs and branches have begun to sprout some kind of growths and the leaves on the affected limbs and branches are wilting. What is this, and how do I stop it?
A: I don’t have good news I’m afraid. The growths are the so-called “toothpicks” that signify an attack by Asian ambrosia beetles. It is hard to predict whether any of the limbs will recover. It all depends on how many beetle holes were made.
If parts of your tree are alive at the end of this summer it would make sense to protect it next year. These beetles emerge in February. Spray the trunk and limbs then with an insecticide that contains permethrin (click for sources) , bifenthrin (click for sources) or deltamethrin (click for sources) and repeat in March.