These mildews are a group of fungi that attack a wide range of vegetables, fruits and ornamentals.

Small, yellow, pale green or brownish spots appear on leaves and cause portions of the leaf to dry out and die. In humid conditions, greyish downy patches develop on the undersides of the leaves under each spot.

Control:
Don't overcrowd plants and avoid overhead watering. Remove and burn affected leaves.

Spray with a fungal spray, wetting the undersides, too. If plants are regularly infected, your climate is probably too humid for them.