Brown Leaf
Spot (fungus - Bipolaris oryzae): This disease, previously called Helminthosporium
leaf spot, is common in Texas. Most conspicuous symptoms of the disease occur
on leaves and glumes of maturing plants. Symptoms also appear on young seedlings
and the panicle branches in older plants. Brown leaf spot is a seed-borne disease.
Leaf spots may be evident shortly after seedling emergence and continue to develop
until maturity. Leaf spots vary in size, are typically 1/8 inch in diameter, and
are circular to oval in shape. The smaller spots are dark brown to reddish brown,
and the larger spots have a darkbrown margin and reddish brown to gray centers.
Damage from brown spot is particularly noticeable when the crop is produced in
nutritionally deficient or otherwise unfavorable soil conditions. Significant
development of brown spot is often indicative of a soil fertility problem. Brown
spot may be reduced by balanced fertilization, crop rotation, and the use of high
quality planting seed. Foliar fungicides are not economical for controlling brown
leaf spot on most commercial long grain varieties. Rice seed with infected glumes
can result in diseased seedlings. Seed treatment fungicides reduce the incidence
and severity of seedling blight caused by this fungus.
