General recommendation for treating mildew

If the mildew is confined to just a few leaves or parts of the plant, I usually recommend they just cut it off and discard. Once it’s on the plant, it’s on the plant for the rest of the season, however, you can reduce the spread by making sure the plant gets plenty of sunlight and good air circulation (don’t jam it closely between other plants). Once the foliage drops in fall, remove it all, discard it, and hopefully the mildew will not recur the following year.