cedar foliage discoloration & loss

Asked August 4, 2020, 12:03 PM EDT

9 years ago I transplanted some small cedars,which over the next few years seemed to do well in growth and health
.A couple of years ago several of them became afflicted with something that caused the foliage to turn orange and drop from the branches.
All but one seems to have recovered with new growth and have sustain good foliage and color for a couple of seasons .
Still one remaining tree seems to be suffering .
In the last few weeks it seems to be afflicted again with the discoloration on the upper section of the tree. The green foliage looks pale and unhealthy compared to the other cedars and the orange color has returned
It was doing well earlier this season with new growth and good color especially on the lowest branches.
There has been, until this past week, a rather lengthy dry spell during which I watered the tree.
It is about 12 ft high with a base trunk diameter of about 6 inches.
What would the tree be suffering from and is there a remedy to return it to a state of healthy foliage growth

New York

3 Responses

Thank you for contacting us. Browning and die-back is a very common complaint with cedars or arborvitae. There are several possible causes but you will need to determine which might apply in your case.

Die-back is often the result of root damage, frequently due to too much or too little water. These trees can turn brown quickly in a drought, and sometimes they do not show signs of branch death until long after the damage occurred. The symptoms may be the result of last year's conditions.

Make sure they receive ample water in both summer and winter. Desiccating winter winds can have the same effect as summer drought. The trees should receive an inch of water per week across the entire drip zone. Long, slow application from a drip irrigation system is best. Test the soil about 2-inches down with your finger. It should feel cool and damp, otherwise, it needs water.

Apply 2 to 3 inches of wood chip mulch across the entire drip zone of the trees, but be sure to pull it several inches away from the trunk to prevent possible rot.

Be sure to irrigate well just prior to when the ground freezes in winter. Cedars are sensitive to dry winds and salt. Sufficient water and wood chip mulch will help prevent this type of damage.

Too much moisture can also cause roots to rot, so good drainage is required.

Another possible cause of browning is a tiny pest called the arborvitae leafminer. This insect feeds within the scale-like leaves, injuring them and eventually causing foliage at branch tips to turn tan, then brown. If detected, cut off and destroy any infested, damaged twigs during fall or winter. Wipe your tools with rubbing alcohol after each cut to prevent spread of plant disease.

For a severe problem, you may wish to contact a certified arborist due to the size of the tree. Leafminer larvae can be sprayed thoroughly in mid-spring and again in late summer with a pesticide containing spinosad. Dilute the concentrate in water according to the product label. Wear gloves to protect your hands, and spray only on a calm day to prevent drift of the insecticide. Be sure to note the protective cautions on the label also.

I cannot say whether your tree will re-foliate at the top. Branches that still have green growth will probably continue to grow, while those that are entirely brown probably will not.

thank you so much for your time ,input and advice.
I will check out the soil condition under the tree but I recall when transplanting all the trees, it is actually very sandy..the drainage is excellent & soil percolation rate is fast..I am not sure if root rot is the cause ..
I did spray with a pesticide called Malathion last year and the year before ,but only once during the warmer season each year ..does this contain spinosad ? if not what product would I look for that contains spinosad. the line of cedars are next to a line of White Pine interspersed with some Balsam Fir...
It is difficult to water the during the winter as the snow is very deep
I have included some new photos

Hello again,

I realize that watering in the winter is not practical. The important thing is to make sure the trees are fully hydrated before the ground freezes. Snowmelt will certainly help to hydrate trees also, but in recent years climate change has diminished the snow accumulation in many regions.

If you are able to confirm the presence of leafminers, do a Google search for spinosad products, and then choose Images. This should show many products that contain spinosad. Spinosad is a naturally-derived product that is more environmentally-friendly than Malathion. However, that is not to imply that it is "safe". It is still necessary to follow the instructions carefully and use all safety precautions.

You may still wish to consult with a certified arborist who can physically inspect your trees and offer an opinion.