mildew. There are sprays (standard fungicides, home made brews and organic options), some work and some don't. Every garden is different so it can be hard to find which one will work for you every time. I would snip off the leaves with the worst case of it and hope it improves the air flow around the plant. It only causes problems when it over whelms the plant.

I just remove the offending leaves.... of whatever is being attacked... mold mildew..

I got rid of aphids and the scales of my Murraya koenigii plant..

Keeping it indoors in winter in a dry environment causes these problems...

So I wait for the problem to be solved on its own, ..However, if it still shows ants crawling up the stems.... it is time to take a hose and hose them down and then pick the scales one by one...:-(