Chocolate spot is a fungal problem affecting broad beans only. Small brown spots appear on the upper surface of broad bean leaves. Dark streaks on stems may be seen. Pods and beans may also be discoloured. Adjacent spots may merge to form large blotches. Severely affected plants may die off. This fungal infection is encouraged by damp or humid air and may overwinter on remains of infected plants.
Grow beans on a well drained site and avoid using high nitrogen plant feed (which will increase the development of soft, infection prone growth). Lift and destroy badly infected plants. Space plants well (at least 23cm apart) to increase air circulation. Ensure good weed control between the rows which should help to minimise humidity and damp air around the plants.
There is currently no chemical registered for the control of chocolate spot on broad beans.