Q: We have two large redbuds. One is in serious trouble due to ambrosia beetles; I sprayed it in late April with insecticide. Now I notice the other has “sawdust toothpicks”. Would a systemic treatment help?

A: Sad to say, there are no systemic insecticides that will kill Asian ambrosia beetles once they are in a tree. The insects are simply too deep for surface or systemic insecticides to hurt them. I have details on homeowner preventative sprays and making a monitoring trap at bit.ly/ambrosiab.