Symptoms
On leaves, elliptical or spindle-shaped lesions (0.5-1.5 x 0.3-0.5 cm), with pointed ends and grey or white centres; dark-green to reddish-brown margins, sometimes with a yellow halo. Under humid conditions, abundant conidia are produced on lesions. In cases of severe infection, lesions coalesce, killing the leaves. Leaf sheaths dry up and whole plants may be killed. Severely infected fields have a scorched appearance.
On resistant rice cultivars, hypersensitive spots or small, round to elliptical, brown lesions are formed.
On leaf collars, rotting may result in premature leaf fall. On lower nodes, rotting causes 'white heads'.
On panicles, all parts of the rachis, rachilla and grains may be infected. Most often, the basal node of the panicle is infected, resulting in 'neck rot' or 'rotten-neck' and 'white heads'. Bluish-grey fungal growth and sporulation occurs over infected regions. Early infection results in white heads or partially filled heads; late infection after grain filling, in 'broken necks'.