They are probably getting ready to go back down for the summer. They don't stay up until winter... they do their thing and then go dormant.

I'm not a plant pathologist but I've also noticed the same desease on an old mayapple bed in my back yard.It seems to get worse every year.I dont even get any fruit anymore.I think starting a new bed in a different area is the solution.Thats what I did.I just transplanted a few root pieces away from the old bed and they grew like weeds without the yellow spots.