Arborvitae problem

Asked August 31, 2020, 8:31 PM EDT

I have a row of fifteen 35' (or so) arborvitae, one of which has browning at the very top. Not sure if it is due to bag worms but there are some scattered throughout the plants. (Only the one plant shows damage.) I have no way of reaching it for a sample or good photo, so I can't be sure what is causing this. If the problem is bag worms and I can hire someone to spray the around the affected area, what chemicals would you suggest? Any other approach? Is there a particular time of year to treat this problem? What about mites or aphids? My PHD in horticulture with experience in entomology friend says the leaves aren't stripped like what happens with bag worms. (He's not up on the current recommended chemical treatment.) I would be sick to lose this beautiful hedge.See photo

Cecil County Maryland

3 Responses

Hi! Thank you for your question. It is hard to tell from the photos submitted what may actually be causing your problem. My guess is that if you are not seeing bagworms hanging on the tree right now, that is probably not it. They would be large and visible this time of year. Bagworms are at the end of their life cycle and treatment won't be effective in control. You need to be very observant in late May and early June for timing of an insecticide application once the bagworms have hatched. We recommend treating the 2nd or 3rd week of June once they have hatched. A very safe treatment like a Bt would work well early. a systemic insecticide would be needed for control later in the season.

You can get problems from wind damage. Is it possible that part of the tree has been damaged? Broken or cracked? Sometimes branches will be damaged, but signs of damage don't always show up immediately, especially if part of it is still getting nutrients. My recommendation is to get an arborist there to take a look and make a connection with them for spraying in the spring if needed. If the top is damaged, the affected area should be removed by pruning properly. If the arborist suspects disease, ask them to retrieve a sample to be submitted to the UD plant diagnostic lab for diagnosis. Or the University of Maryland Plant Diagnosis Lab - Karen Rane is a very good pathologist.
You can look for certified arborist in the Delaware Nursery and Landscape Association's website directory - or look for one in Maryland. I hope this is helpful! Best regards, Tracy

Thank you for the information. I will consider it all fully. I did state in my original message that bag worms are scattered throughout the bushes, so the damage can still be from them. I have dealt with various landscape people but never an arborist. Can you recommend any in the Newark/Elkton area? (I am out near Fair Hill.)

Hi! I can't recommend one company specifically - we are unbiased in our information. I would recommend searching for tree companies with certified arborists and I am sure there will be companies that are suggested. If you would like to check their certification, you can contact the International Society of Arborists
Good luck!