Bean rust

What you see

Small rusty-brown pustules on the leaf underside, each ringed by a pale yellow halo, that rub off orange on your finger. Heavy attacks brown the whole leaf and defoliate the plant from the bottom up.

Conditions

Warm days, cool humid nights, and long dew periods - so it arrives in late summer and autumn. Dense stands that never dry are worst affected.

Treatment

Remove and bin affected lower leaves. Sulphur or a bicarbonate spray checks it if applied early. Late in the season it is usually not worth treating at all.

Prevention

Wide spacing on a windy site, morning watering at the base, and clearing all bean debris in autumn. Rotate two to three years.

Months: July, August, September, October

Plants

Green bean, Runner bean, Broad bean

Remedies

Wettable sulphur, Potassium bicarbonate spray, Bordeaux mixture (copper)

The thing people get wrong

Bean rust in September is usually not worth a single minute of your time - the plants are within weeks of finishing anyway and the pods are unaffected. The judgement worth making is timing: rust in July on a crop with two months left is worth treating; rust in September is a signal to pick the last beans and pull the plants.