Pustules rupture tissue, exposing powdery, brick red mass of summer spores. Puccinia graminis has many specialized varieties. P. graminis tritici attacks wheat and barley. P. graminis avenae occurs chiefly on oats. P. graminis secalis occurs chiefly on rye.
Alternate host is common barberry, a tall erect woody shrub with bristle-toothed leaves.
About a week after infection, the fungus sporulates within the lesion producing a dark, gray powdery appearance. At heading, blast kills the entire panicle before grain fill is complete. Prevention Resistant varieties are readily available, e.g., Katy, Kaybonnet, and Drew. Blast damage can be prevented or greatly reduced by proper irrigation. Rice blast, which was code named II at the time, was part of US stockpile prior to 1972.