Brown spot

The first symptoms of brown spot disease are small, circular, dark-brown lesions on the lower leaves of field plants and sometimes on old seedlings or the senescing leaves of transplants. The lesions enlarge as the leaves mature and are surrounded by an irregular, yellow halo. The halo is caused by the secretion of toxins. Often there are numerous lesions, about 25 mm in diameter, which may coalesce and affect more than 80% of the leaf area. Large lesions may have numerous small, satellite circular lesions in their vicinity, arising from conidia washed off the main lesion.