I would have a certified arborist in your area inspect the trees. Summer drought probably put those trees in stress and they should be looked at. You may have more than one problem. An onsite inspection should run around $75. Well worth the investment. Best And Happy Yardening, Nancy.
Arborvitae With Borers And Likely Stress
Question From: l. drew - ARKANSAS
Q: we have over 30 arborvitae approx 10 ft tall growing in a row for privacy. after receiving 9.5 inches of snow my husband noticed one branch that did not come back up and saw the branch crumbled under inspection. so we are aware now that we have a borer in our trees. we spray 2 times a year with volc oil, but need to know what we can do now in january to protect this huge investment of trees.