Question From: N. Lowes - Sault Ste. Marie, Michigan, United States
Q: Wasp or hornets and flies are eating my mountain ash tree bark. Help
European hornets ( Vespa crabro) are the likely culprits. Spray the tree with a dormant oil to kill the over wintering nymphs. For professional help, which is recommended if you have a large tree, contact your local certified arborist. Best And Happy Yardening, Nancy.