Late Summer Ambrosia Beetle Attacks

— Written By and last updated by Carol Hicks

Frass toothpicks and sawdust collected in the crotch of a crape myrtle tree. Photo: SD Frank

Granulate ambrosia beetles are primary pests of nurseries in spring. However, it seems like every year folks report ambrosia beetle attacks on landscape trees in late summer. It is usually not clear if these are granulate ambrosia beetles but there are dozens of related species that do similar looking damage. In this case I found a row of crape myrtles that all had dozens of holes and the tell-tale frass toothpicks. These four crape myrtles were planted between the sidewalk and street but so are many of the 17,000 crape myrtles in Raleigh. So why these four? Why not the dogwoods planted a few feet away? Dogwoods are very suseptible to ambrosia beetles. Who knows? In any case it is not clear what will happen to these trees. Generally trees attacked by ambrosia beetles die because 1) they are full of holes and 2) the ambrosia fungus interferes with vascular transport. I will watch these trees for the next year or two to find out. In general though this is not a reason to spray all the trees in a landscape. Ambrosia beetles target stressed trees and home in on them very specifically.