Thuja Plicata #416855 - Ask Extension

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Thuja Plicata #416855

Asked July 25, 2017, 7:49 PM EDT

I have a 5 year old Thuja Plicata, 15 feet tall, where the outer leaves have started to turn yellow in the past few weeks. The leaves close to the trunk are still green. I lost another thuja tree about 2 years ago when it turned yellow. All the other Thuja trees in the row are still green. I have enclosed a picture of it next to one that is still green as comparison. I have also enclosed a picture of the leaf and the underside of the leaf. I cannot see any insect damage.

Prince George's County Maryland

Expert Response

We viewed your photos. This does not look like a disease or insect issue. This looks like a type of root problem. Some issues you may be dealing with are site problems, root competition for moisture and nutrients from the other trees, poor genetics (weakened root system from the start), planting techniques, planting too deeply, root system rootbound in the container, etc.
Take a look at our publication on these types of problems http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG86%20Common%20Abio...
 See our website for information on planting techniques and post planting care http://extension.umd.edu/hgic/trees-and-shrubs/planting-process

All you can do is keep watered during dry periods and make sure mulch is no thicker than several inches and away from the trunk.. Looks like there is no mulch around the root system. Most likely you will have to replace the tree.

In the future it is a good idea to have a mix of different tree species so you do not lose the  whole stand to a disease or insect issue. Also, if you have to replace the same tree species, the size may not be as noticeable. 
mh

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