DiseasePeronospora farinosa f.sp. betae
Downy Mildew
Duggsopp
How to recognise it
Pale yellow or brown patches on the upper leaf surface, with a corresponding grey-purple downy growth on the underside. Favoured by cool, humid weather and poor air circulation.
Prevention
Space plants generously (rows at least 40 cm apart) to maximise airflow. Avoid overhead watering; water at the base in the morning so foliage stays dry. Do not compost affected material.
Treatment
Remove and destroy affected leaves immediately; do not compost. Improve airflow around remaining plants. A copper-based fungicide can slow spread in severe cases, but cultural measures are more effective long-term.