Stem Rot Symptoms on Rice
Stem Rot (fungus - Sclerotium oryzae): Stem
rot becomes most noticeable in rice fields during the latter stages of
maturity. The disease occurs in circular to irregular areas in
fields and causes premature death and lodging of the plants. The
fungus attacks the rice plant near the water line usually during
late tillering or early reproductive stages of growth. It first
causes black, rectangular lesions with distinct angular borders on
the leaf sheath. Later the lesions become larger, more diffuse,
irregular in shape, and penetrate deep into the culm. As rice
approaches maturity, injury to the stems increases and reaches its
peak at harvest. Weakened stalks break during this stage and
plants lodge making harvest difficult. Plants infected early yield poorly. Ratoon cropping in
many areas is impractical because of the high percentage of plants killed by the disease.
Diagnosis is confirmed by obtaining an infected plant, splitting the base of
the stem, and observing the presence of tiny, black sclerotia in
internal stem tissues. Control measures include the following:
crop rotation, use of early maturing varieties, fluctuating the
flood water level, avoiding excessive rates of nitrogen, and rice
stubble destruction. Some fungicides help to suppress this disease
but are not highly effective.
February, 1996
