A few years ago, my husband and I added two Eastern redbuds (Cercis canadensis) to our front yard. Each spring, I look forward to their tiny magenta flowers followed by the emergence of heart-shaped leaves. This year, one of the two had only a few flowers and was extremely slow to leaf out.
At a distance, the tree seemed healthy, but closer inspection revealed the problem. Several toothpick-like structures were visible along the trunk and branches, the telltale sign of ambrosia beetles. Learning this was rather devastating since there aren’t any ways to manage beetle infestations. The tree came down, and I was determined to make our loss a learning experience for others.
A toothpick-like frass tube emerging from a dogwood trunk.
Terasa Lott, ©2021, Clemson Extension
After removing the tree, we cut away wood areas near the frass tubes to locate beetles, their galleries, and developing larvae. Considering adult females are about 1/8” in length, it was a bit like searching for a needle in a haystack. We successfully extracted a few adults and some larvae, which Dr. David Coyle identified as granulate ambrosia beetles (Xylosandrus crassiusculus).
Larvae of granulate ambrosia beetles inside a dogwood stem.
Terasa Lott, ©2021, Clemson Extension
Adult granulate ambrosia beetle next to a dime for scale.
Terasa Lott, ©2021, Clemson Extension
The good news is you can protect your trees from these invaders. Most ambrosia beetles are attracted to airborne chemicals produced by stressed trees, so prevention is as simple as keeping your trees healthy.
Tips for tree health:
- Maintain a 2-3” layer of organic mulch. Mulch should extend to the tree’s dripline.
- Provide adequate water during establishment and supplemental irrigation as needed.
- Fertilize based on a soil sample analysis.
- Protect the tree from mechanical damage and avoid soil compaction from traffic.
To learn more, see HGIC 2018, Ambrosia Beetles, and HGIC 1037, Tree Maintenance.
