It is about to bloom but what is the stuff on the leaves? It has been like this for a while but now worse.

Looks like powdery mildew: http://www.missouribotanicalga...

Definitely looks the same. Thanks for the informative link.

Yes, powdery mildew.

I have had relatively good luck ridding plants of powdery mildew by spraying them with a milk solution.
One part milk to 9 parts water.Measure does not have to be exact. I have found whole milk does a better job than skim and it needs more than one application 2-3 does it for me.
I have used this mostly on phlox and a few other plants ,I have goldenrod only in the wild areas of the garden and they do not get much attention.

I dug it up and cut back all the infected leaves. It is hard to believe it does not get enough sun but I will try it in one more place. Maybe it is a weak hybrid of goldenrod. It is solidago rugosa "fireworks"

I have 'Fireworks'. It is subject to powdery mildew. Mine is a strong grower - very strong, but they are susceptible.

Do you have it full sun with lots of air circulation? It really looks like fireworks, so worth it to pamper it a bit