Identification: Dieback on row of Cedars

Hello,

Along the side of my property I have been battling dieback on my row of cedars the last 3 years. Several plants have been relaced as well. I was originally told it was related to mites. The last two seasons the mites have been targeted with miticides and I believe controlled. Looking with a microscope I see very little insect pressure.

In South Western Ontario we have humid summers. The side where the dieback occurs is shaded and the lawn is irrigated. I am starting to wonder if this can be related to disease rather than insects.

Any advice or input is welcome.

Thank you in advance.

Derek

 

When you look up close at the leaf scales, the ones affected and browning, do you see any tiny holes?

 

They're arborvitae (Thuja occidentalis) not cedars (Cedrus spp.).

It does look more like a fungal disease, but hard to tell without microscopic examination. Shade doesn't help either, they'll always be thin and open where they don't get enough sun.