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Lesions first appear as very small, oblong to round yellowish spots on the leaf
blade, leaf sheath, stalk and, occasionally, the outer ear husks and tassels of
maize. Lesions may occur in bands across the leaf blade. The spots seldom
become greater than 1 mm in diameter except where two or more of them coalesce,
and they may become so numerous as to give the entire leaf blade a rusty
appearance (Tisdale, 1919). Infected tissues within the lesion turn
chocolate-brown to reddish-brown and lesions coalesce to form large, irregular,
angular blotches. Cells of infected tissues disintegrate and expose dusty
pustules containing large numbers of golden-brown to dark-brown sporangia. The
entire leaf sheath may become brown because of the coalescence of large numbers
of lesions. Where infections are this numerous, the entire leaf is often killed
before the plant becomes mature (Tisdale, 1919).
On the stalks, water-soaked lesions may be seen beneath the leaf sheath. Lesions may coalesce to form brown blotches, and later, small pockets of brown sporangia form in the stalks. Stalks may be completely girdled at the nodes and they are easily broken by the wind following invasion of the tissue by the fungus (Tisdale, 1919).
Brown spots appeared on maize leaves when injured roots were inoculated with a sporangial suspension of Physoderma maydis. Symptoms also appeared on the leaves when injured collar regions at the base of the stem just above the soil level were inoculated (Lal and Chakravarti, 1977a).
Cultural Control and Sanitary Methods
Destruction of crop residues has had a significant impact on brown spot severity in the next crop. For example, brown spot developed in susceptible maize inbreds and hybrids planted in overwintered debris in 1972; in contrast, little or no disease occurred where infested debris was ploughed in (Burns and Shurtleff, 1973 ).
Resistance exists in genotypes of maize throughout the world (Thompson et al., 1963; Brewbaker, 1975; Aujla et al., 1976; Lal and Chakravarti, 1977c; Kaiser and Prodhan, 1990). Resistance is inherited by additive and dominant effects, but additive effects are more significant (Moll et al., 1963; Thompson et al., 1963; Thompson, 1969).
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
P. maydis is an important disease in areas of abundant rain and high
temperatures. Yield losses of 20% have been reported in India (Lal and
Chakravarti, 1976). It is normally a minor problem in the USA. Losses of 6-10%
were reported in North Carolina in 1919 (Tisdale, 1919), and 1.9% in
Mississippi in 1957 (Broyles, 1959). In 1971, a severe outbreak occurred in
white maize in Illinois, with 80% lodging in some fields (Burns and Shurtleff,