Is anyone having mildew issues with this plant. It is in full sun for about 5-6 hours. I'm in zone 6B

I just Googled and they can be susceptible to mildew (probably due to their arching growth habit blocking sun and air circulation underneath). I'd spray with water mixed with a little sudsy liquid dish soap and try to get the spray up underneath the branches as well. That's what I use on my crape myrtles when they fall prey to powdery mildew after rainy spells.

I've had one for about 4 years in a sunny spot [zone 7, Long Island]. It's grown really big with zero issues. It has tons of white flowers that are turning cherry red now, the only issue is its crowding out daylillies around it.

Mine is 10 years old, also zone 7, Long Island, and had mildew just one wet fall.

No problems with mine that are grown in full blazing sun with no neighbors encroaching on their sun space. I have noticed that it does not tolerate shading -- it will lose the competition for light.

SE Michigan, I have 6 ninebarks with no signs of mildew. However, this season seems to be ideal for mildew. I have many many peonies that look terrible. Usually I only get a dozen or so peonies with mildew. This year I have several dozen. Actually, one of my mildew peonies is right next to one of my ninebarks. Ninebark look great.

My ninebarks have also been mildew free all these years and they are directly under a couple maple trees with a retaining wall at their backs.