KnockOut Rose dying- black spot?

[Izzie]

In my quest for finding some roses that will happily overwinter in CO, I'm trying my first root-rose (as opposed to grafted). (next experiment is a David Austen)
The Knock Out family of roses has had great success in CO.

I purchased it's original member from a reputable local grower: Rosa 'Radrazz' The Knock Out® Rose from Conard Pyle
In true "Izzie" fashion, I spent nearly 20 min looking at each one available until I found one that I deemed healthiest and worthy.

But it immediately started pouting and looking diseased after we potted it.


Took it out of it's original black bucket and potted into a large insulated plastic pot that doesn't get super hot in the sun- it's about 20"x17".

Soil: 1:1 ECO compost: Moisture Control Soil by Miracle Grow

We've never had problems with this mix.


I don't have pictures yet, I'll take some as soon as it stops raining.

It looks very similar to Black Spot. The bush is being defoliated pretty quickly. I have not been able to find any pests.


I've treated with a systemic Ortho rose disease product, with no effect after a week.

Any tips on how to attack this? I've never had to deal with black spot before- just been lucky.

Will Neem Oil put a dent in it?

Should I do antifungal sprays or steer towards antifungal systemics?

It would be a shame to lose this sweet plant so soon.