Chocolate spot

What you see

Small reddish-brown chocolate-coloured spots peppering the leaves, stems and pods. In a bad year the spots run together, the whole plant blackens and collapses, and the pods fail to fill.

Conditions

Mild, wet, humid weather on a crowded stand - classic for autumn-sown broad beans through a wet Atlantic winter. Potassium-poor and waterlogged soils make it far worse.

Treatment

Remove the worst affected leaves and improve airflow. Copper gives some protection. Feed with a potassium source - a plant with adequate potassium resists it noticeably better.

Prevention

Sow in well-drained ground with wide spacing. Do not overfeed nitrogen. Autumn-sown beans in a wet site are the highest-risk combination, so consider a spring sowing instead.

Months: December, January, February, March, April, May

Plants

Broad bean, Green bean, Peas

Remedies

Bordeaux mixture (copper), Wood ash, Seaweed extract

The thing people get wrong

The spots themselves are near-universal on overwintered broad beans and largely harmless - what matters is whether they stay as discrete spots or merge into blackened tissue. That transition is driven by plant nutrition as much as weather: potassium-starved beans on wet ground go from spotted to dead, well-fed beans on drained ground stay merely spotty and still crop.