brown spots on arborvitae

Asked July 8, 2014, 2:48 PM EDT

Dear Sir/Madam, I have about 10 arborvitae trees (?) (evergreens that are ~10 feet tall) growing along my driveway pretty close to each other forming a “natural fence”. A couple months ago one of the trees started to develop brown spot somewhere in the middle, while other part of the tree remained healthy. This dry spot is growing and seems to be contagious – neighbor trees started to develop brownish spots. Pictures are attached. Would you please advise how to save the trees? Thank you in advance, Maxim Soloviev

New Castle County Delaware

1 Response

Thank you for using Ask-An-Expert to help with your arborvitae problem. From the photo it looks like your tree has signs of a disease, but it also could be a result of red spider mites. The best way to get an accurate diagnosis is to bring a sample of the dying section & adjacent live section into our UD-Cooperative Extension New Castle County office. The address is: 461 Wyoming Road, Newark, DE ... phone: 302-831-2506.

Depending on the exact arborvitae species, these trees may have been planted too close. The lack-of-sufficient air space between plants fosters an environment for disease. Once limbs of arborvitae become intertwined and sunlight is unable to reach the foliage, the plant stops producing foliage in that area and concentrates growth where sunlight and photosynthesis can take place.

I hope you are able to find-out what is causing the problem and begin corrective action to help sustain your tree plantings. ~DOT