What happened to my arborvitae shrubs?

[Charles Ho]

Two things happened to my arborvitae shrubs and I don't know why (I included pictures). I'm pretty much a novice about this stuff

1) One single tree died out of a long line of them. Strange how just one shrub out of a row died, doesn't seem like it's insects or anything as it didn't spread across the row of them. Is there any way to nurse it back to health or should I just replace it?

2) In one section of the row, the shrubs have gotten thin and bare. Again don't know why it is happening to just one section. I fertilize and water them all equally. Again, can I nurse them back to health, or should I just replace them?

By the way, this is a great forum with really helpful people. Thanks!

 

[Zale]

Wrong plant for the space it is in. Shearing them doesn't help either. I would pull them and install a upright form of taxus.

 

[BC WetCoast]

We deal a lot with arborvitae and when we see a single stem death, it's either a weak individual (think of individual trees as people, where some people seem to be more susceptible to illness) or armillaria, which is a root rot.

If you peel the bark back at the ground line and see a white mat just under the bark, then it's armillaria.

If you have a section of trees that are doing poorly, what I've seen is too much shade. Although naturally they are shade tolerant, they become sparse in too much shade.

They can handle a lot of shearing, but it looks like they have been sheared too hard on the sides in the past. I have found the varieties - Smradg or Brandon work best for hedges.