Black rot

Worst in warm, wet weather through the main brassica season, spring and summer.

Black rot is a bacterial disease of brassicas that turns leaf edges yellow then brown in a telltale V-shape and blackens the veins. It spreads in warm wet weather and on splashing water, seed and tools, and there is no cure, so clean seed and rotation are the defence.

How to identify

• Yellow V-shaped wedges spreading in from the leaf margins
• Black, darkened veins running through the affected wedges
• Leaves browning, wilting and dropping as it advances
• A foul-smelling rot in heads and stems in bad cases

How to prevent

• Use clean, certified disease-free brassica seed and seedlings
• Rotate brassicas on a long cycle and clear all crop debris
• Water at the base and avoid wetting and splashing foliage
• Do not work among brassicas while they are wet

How to control organically

• Pull out and bin infected plants whole, never composting them
• Avoid handling wet plants to stop spreading the bacteria
• Disinfect tools and stakes used around infected plants
• Rest the bed from brassicas for a few years
• Improve airflow and drainage to slow further spread