|No one is monitoring this website. I'm still waiting to see an authoritative comment on my previous question about Diablo Ninebark mold.
|I'm sorry if you did not receive a response earlier. Unfortunately, we have no way to go back and resend our answers. Based on the information in your question now, I suspect your plant may be suffering from a fungal infection such as mildew. Ninebark is occasionally subject to mildew problems when the weather conditions are conducive to it. You can try removing affected leaves and spraying to control it, however it is difficult to control once it has become widespread on the plant.
In general, preventive measures can help. Make sure the plant is sited in a spot with good air circulation and thin the plant each spring so that air can circulate within the shrub. Also avoid wetting the foliage should you need to water the shrub. A thorough cleanup of fallen leaves in the fall as well as any prunings is also useful in limiting sources of reinfection.
If it reappears next year, immediately remove the affected foliage and consider a spray program. Your local county extension should be able to confirm the diagnosis and based on knowing that, advise you on what to use and how/when is best to apply it for maximum results.