We have a row of Arborvitae in which some are turning brown. Hopefully we've watered them sufficiently and one member of the family has worked in a nursery and knows red spider when she sees them, and there are no red spider. We did have to take out several arborvitae last year and repurposed the trunks into a primitive split rail zig-zag fence at the foot of the row of arborvitae bushes. Could there be something (as in bugs or disease) in the dead trunks that has moved from the dead and downed bushes to the living ones?
Benton County Oregon
Your arborvitae could be suffering from a disease or be insect related. There are several diseases that cause browning of branches and more insects than red mites that can invade them. Water either too much or not enough is frequently the issue with them. The abnormally hot summers we have had for the last couple of years could have stressed your trees if they were not regularly watered. The extremely wet winter we just experienced could have drowned the roots or caused root rot to set in if the soil stayed saturated for a prolonged time period. I suggest that you take samples in to the master gardener help desk of your plants and some photos of the entire stand of trees to help you determine what is causing your issues. A timeline of when the problem started would be helpful. Until a cause is determined for what is causing the death of the trees you have already lost I do not want to speculate if ‘something’ is traveling from your repurposed wood that you used in your split rail fence. The Benton County Master Gardener help desk is located in the OSU Extension Office at 4077 SW Research Way in Corvallis. Phone is 541-766-3549. I suggest calling before taking a sample in to ensure that a Master Gardener is on duty. Don’t forget the photos!