Sheath Rot

Causative agent

Fungus, Sarocladium oryzae. 

affects most prevailing rice varieties.

usually minor, affecting scattered tillers in a field.

Occasionally, larger areas of a field may have significant damage. 

Plant parts and life stages affected

Uppermost leaf sheaths that enclose the young panicle during the boot stage

Symptoms

Lesions are oblong or irregular oval spots with gray or light-brown centers and a dark reddish-brown, diffuse margin, (a typical  irregular target pattern). 

Usually expressed as a reddish-brown discoloration of the flag-leaf sheath.

Early or severe infections affect the panicle causing the panicle to emerge partially. The un-emerged portion of the panicle rots, turning florets to red-brown – dark brown.

Grains from damaged panicles are discolored reddish-brown to dark brown and may not fill.

A powdery white growth consisting of spores and hyphae of the pathogen may be observed on the adaxial surface of affected sheaths.