Emerald Cedars turning brown


I planted 10 6-7 ft emerald cedars in the spring. I live in an area on Vancouver Island that sees a fair bit of moisture just a few hundred feet from the ocean (eastern side). The trees seemed to be doing okay until severe browning started occurring this September. I started taking the brown off by hand and noticed at the bottom it looked like a blackening as though a few branches had been torched which is not the case. Also wood ticks(the gray shelled looking insects) were lodging up where the dead needles were collecting. Their larvae was also set up in the main trunk of the trees. I’m sure this must be the problem and want to know what to do about it.


It sounds like you might have a couple of issues with your Thuja occidentalis ‘Smaragd’ or Emerald/Eastern White cedars.  Dieback of cedars is often not the result of one single cause, but a combination of stresses.

The blackening at the base could be the result of a foliar blight called Keithia blight.  This is caused by the fungus Didymascella thujina.  According to the BC Ministry of Agriculture, infected leaf scales have small, black, circular shotholes that often turn white. The foliage turns brown and drops, leaving branches bare. Small trees and seedlings can be killed entirely but mature landscape trees are less severely affected. On mature trees in dense stands and damp or shaded areas, low branches can appear scorched. Upper branches are less affected. In the landscape, the disease can be controlled with fungicides if necessary. They recommend applying a product containing fixed copper, zineb or mancozeb every 2 weeks from late March to mid-June, especially during wet weather.

Your description of a gray shelled wood tick could be possibly be a Redwood Bark Beetle which feeds on both red and white cedars and is found in coastal locations from Alaska to southern California.  Its larvae are white, legless with a pale brown head and the adults are brown to black in colour.  The female beetles attack already weakened trees by boring into the bark to lay her eggs.  Can you see any small holes of about 1.5-2mm in size to indicate that this has occured?  Unfortunately the recommended control for this insect is prevention.  For a list of other possible insect invasions, please refer to the Forest Pest Leaflet- Common Insects Damaging Junipers, Cedars and Cypresses in British Columbia at https://cfs.nrcan.gc.ca/pubwarehouse/pdfs/4593.pdf.

For further information that might be more specific to your area, contact the Vancouver Island Master Gardeners Association at  https://www.mgabc.org/content/vancouver-island-vimga .  This website includes a list of community clinics where you might bring a sample for an MG to view.