Chocolate spot

Chocolate spot is caused by two Botryotinia fungi; Botrytis cinerea affects crops intermittently, and is usually confined to flowering whilst Botrytis fabae is prevalent throughout the season. B. cinerea is more virulent, producing a 3% reduction in yield per percent disease infection whilst the mean yield loss from B. fabae is 0.5% per percent disease infection.

Symptoms
Disease infection appears as dark brown lesions, which enlarge and coalesce, usually occurring on the lower leaves first, moving to the middle and then upper canopy. Disease growth is optimal when temperatures of 15°C (59°F) and relative humidities of more than 85% predominate. Chocolate spot is generally associated with wet seasons and dense crops. Field beans in common with most pulses supply the assimilates for seed growth at each node from the leaves subtending that node. Thus, a strong relationship exists between disease infection in the podding region and seed yield.

Prevention
Control must be a programmed approach including preventative fungicides applied to each layer of the crop canopy throughout its expansion. Similar relationships exist for other Ascochyta and rust.