Symptoms
Symptoms begin as pin-point to small (up to
1/4 inch), irregular, red-brown spots which
appear on unifoliate leaves 2 to 3 weeks
after planting (Figure 1). Spots appear on
both leaf surfaces, but they tend to be more
pronounced on the lower surface. Individual
spots may coalesce to form larger blackishbrown
irregular blotches. Numerous spots
cause leaves to yellow and drop from plants;
yellowing and defoliation are the result of a
host-specific toxin produced by the fungus
in diseased tissue. Spotting occurs most
prominently on unifoliolate leaves of young
plants (Figure 2) or throughout the canopy
during pod fill to maturation (Figure 3).
Brown spot is often confused with a bacterial
disease, bacterial leaf blight (Figure 4).