That appears to be a fungal disease - you can see the fungal spores (black dots) on the reverse of the needles. Tsuga are prone to a couple of needle blights but most common is Fabrella tsugae.

I thought that too. I think, with doing some research, that is is circular scale. Can anyone confirm that? Treatment is dinoetefuran.

You can confirm yourself :-) Do they scrape off? Scale will scrape off easily with your finger nail but fungal spores not so much (more dusty than a single entire organism like the scale).

They scrape off really easily. Like flakes. So I guess that confirms scale. Anyone have treatment recommendations? I've found the dinotefuran online and of course it's expensive.

Horticultural oil is routinely suggested as a control for scale, however its timing of application is critical. You want to apply when the insect is in its crawler stage and these are usually in abundance from mid May through early June. However, effective management of this pest is extremely difficult since all
stages of development may be present during the growing season. There is
an abundance of crawlers from late May through early June. Repeat applications may need to be made for effective crawler management
until mid-September. Maintaining healthy trees may reduce the chances
of an increase in the population of this pest. Research has demonstrated
that nitrogen fertilization of hemlocks enhanced population increases
of this armored scale so back off on any planned fertilizing.

Neem oil can also work.

I found a product called Green Light (Scott's) Ash Borer killer. It has 2% dinotefuran and seems to have good feedback from those treating scale. It's not the 20% kind arborists recommend but that stuff is over $100. And it's a small conifer so I'll never need that much. I know it's still early in the season and they haven't gotten active yet. I've got other small tsuga candensis planted in the same area so I want to treat it and get it under control. The dinotefuran is systemic so it will continue to kill all year long.

What's the mode of application? Also, just as a point of interest, that and most all other neonicotinoids-for better or for worse-are likely not long in the marketplace.

unless its some prime specimen ... just getting rid of it is often the simplest alternative ...

dont spend 50 bucks on oils.. sprayers.. and your precious time ... repeatedly over a few years ... to save a 20 buck plant ... unless of course.. you have all the stuff sitting around anyway ..

especially if a chemical solution is advised .. often.. its not worth the minor exposure ... [which is not the case here]

ken

It's a rare tsuga. At least for me. I searched for over a year to find one and I'm not ready to let it die or kill it. I'd rather kill the pest.

If you go w/gardengal's recommendation, any oil or Neem has to be applied underneath the needles, which can be difficult. Top of the needles won't work.