Stem rot

Causal organism: Helminthosporium sigmoideum var. irregular (Leptospheria salvinic or Magnaportha salvinii)

• High nitrogen levels increase stem rot but potassium reduces the harmful effect of excessive nitrogen.
• Phosphorus also stimulates the disease but with less effect.
• Silica inhibits the disease.
• The disease incidence is two or three times higher on plants infested by stem borers.

                         

Symptoms:

• Stem rot stars with small, blackish irregular lesions on the outer leaf sheath near the water level at the later growth stages of the rice plant.
• The fungus penetrates the inner leaf sheath and finally the leaf rots and sclerotia are formed.
• Further advance of the fungus causes infection on the stem.
• One or two internodes of the stem rot and collapse leaving only the epidermis and vascular bundles.
• Small back sclerotia dots are inside split internodes.

Management:

• Burn rice stubbles and infected straw.
• Avoid continuous flooding of field.
• Grow resistant varieties such as dudshar of Bengal, seri Raja, Lembu Basah, Machang, Ramined str 3, BPI- 76 and Hondurawada.