nurtomiDowny mildew
Yellow patches with growth underneath deserve a closer look.
What to look for
Depending on the plant, upper leaf surfaces can develop yellow or angular patches while gray or purplish growth appears underneath in humid conditions. Many leaf problems look similar, so inspect both sides.
What to do
Separate the affected plant when practical, remove affected leaves and avoid wetting foliage. Improve spacing and inspect new growth. Seek plant-specific advice if the problem spreads.