Arborvitae Hedge Sudden Death: Herbicide Damage Suspected

Indiana Hedge: Solid Brown Dead Zone on Neighbor Side

15-year-old arborvitae hedge (37 plants). Backside of east hedge: solid brown dead leaves/branches bottom 3 ft. After heavy rain 9/23, fine. 9/28 mowing noticed death. Different pattern spreading forward. Power-washed, removed dead/mulch. Sporadic browning on other side too.

Primary Suspect: Herbicide Damage

Uniform pattern suggests herbicide. Any lawn care applications nearby?

Note from Expert

Diagnosis via internet is hard. Started with photo question; user gave low feedback rating despite detailed answer.