Sheath Spot Symptoms on Rice
Sheath Spot (fungus - Rhizoctonia oryzae): This disease is similar to the early
stages of sheath blight and is caused by a related fungus. Small sclerotia initiate the
disease on the outermost leaf sheath. A reddish-brown lesion develops on the
plant near the waterline. During internode elongation, the sheath spot may be pushed up above
the waterline because of this new growth. With age, the lesion enlarges slightly to
assume an eliptical to irregular shape (1/2 to 1 inch long) with a distinct purple-brown
border and a tan-to-straw colored center. The sheath spot fungus does not develop on the leaf
blades as is the case with sheath blight. Rather it remains on the outer sheath only.
Sometimes the fungus will cause a yellowing of the leaf attached to the sheath it has infected.
Some reduction in yield may occur in tillers that are infected; however, it is
generally minor and too few tillers are affected to result in a significant yield loss.
February, 1996
