Downy mildew
Pale blotches on top of the leaves and fuzzy growth underneath, after cool, damp nights.
What you'll see
- Pale green, yellow, purple or brown blotches on the upper leaf, often boxed in by the veins.
- Fuzzy white, gray or purplish growth under the blotches, mainly after damp nights.
- Leaves shrivel and drop, and plants such as impatiens can die.
Why it happens
Downy mildews are water molds, not true fungi. They need leaves that stay wet for hours in cool, humid weather.
How to fix it
- Pick off affected leaves as soon as you see them, and bin them rather than composting.
- Remove badly infected plants.
- Thin plants and water early, at the base, so the leaves dry quickly.
Keep it from coming back
- Avoid overhead and evening watering.
- Choose resistant varieties where you can.
- Don't replant the same kind of plant in that spot for at least a year.
Sources
General guidance, not a diagnosis. For valuable, edible or outdoor crops, check with a local extension service or plant expert. Use any product exactly as its label says, and keep children and pets away while it dries.