Downy mildew

A cool-season fungal-like disease showing yellow patches on the upper leaf with a greyish-purple fuzz beneath, worst in damp, still weather.

Angular yellow blotches on top of the leaf, fuzzy grey-purple growth underneath, in cool wet spells.

Remove affected leaves, improve airflow and stop overhead watering. Harvest leafy crops promptly.

Space plants, water in the morning at the base, and avoid crowding through the wet season.