Brown Spot

Causative agent

Fungus Cochliobolus miyabeanus (Bipolaris oryzae)

Plant parts and life stages affected

Coleoptiles, leaves, leaf sheath, immature florets, branches of the panicle, glumes, and grains are affected.

Spots are present in plants at emergence; however, the disease is more prevalent as the plants approach maturity and the leaves begin to senesce.

It is a seed born disease.

Yield losses from leaf infection or leaf spots are probably not serious. Economic losses occur when the fungus attacks the panicle, including the grain. 

Symptoms

The fungus causes brown, circular to oval spots on the coleoptiles which may lead to seedling blight.

Seedling blight may cause sparse or inadequate stands and feeble plants.

The spots are smaller on young leaves, than on upper leaves.

Size and shape of the spots may vary from minute dark (dark brown to reddish brown) spots to large oval to circular spots (having dark brown margin and a light, reddish-brown or gray center). 

The spots on the leaf sheath and hulls are similar to those on the leaves. 

When the glumes are infected,  a general black discoloration could be observed.

When the immature florets are attacked, grain development might het hindered or kernels that are of light weight or chalky may result.