Widespread distribution. North and South America, Asia, Oceania. A damaging fungal disease.
First, on older, outer, leaves - yellow spots with grey centres, up to 12mm diam., developing into a blight. Later, on the stalks.
Spread by rain splash, on wind and on seed. Survival in crop debris and seed.
Cultural control: seed treatment: hot water (48°C for 30 min), but only treat seed <3 years’ old; in nursery, use pasteurised or soilless mixes; use wide spacing and raised beds to improve air circulation in field; use drip not overhead irrigation; plough in remains at harvest, or collect and burn.
Chemical control: seed - thiram; field – chlorothalonil, mancozeb, copper; or those in strobilurin, DMI (demethylation inhibitor) groups of fungicides, alternating with the first any of the first three.