Question
we noticed some sawdust like residue on the ground under a locust tree and also a willow tree. We do not see any bugs or beetles. Is there something we can spray on the ground to kill whatever is attacking the trees?

Answer
You can spray the trunk with an insecticide called Onyx or Merit. Both of these will kill any insect that is boring into the trunk leaving the sawdust. Check with your local nursery/garden type store fro these. Spraying on the ground will not do any good since they are boring into the trunk.