Black scurf: Rhizoctonia solani
Symptom:
- Black speck, black speck scab, russet scab on tubers.
- At the time of sprouting dark brown colour appears on the eyes.
- Affected Xylem tissue causes to wilting of plants.
- Infected tuber contains russeting of the skin.
- Hard dry rot with browning on internal tissue.
- Seed tubers are a source of spread. Moderately cool, wet weather and temp 23 °C are the favourites for the development of the disease.
Identification of pathogen:
Mode of spread and survival:
- The sclerotia on the seed tubers is the principal source of infection of the subsequent crop raised with these tubers.
- On the return of favourable conditions, the mycelium present in the soil may develop producing new hypae.
Management:
- Disease-free seed tubers alone should be planted.
- If there is a slight infection of black scurf that can be controlled by treating seed tubers with mercuric chloride solution for 1.5 hr with acidulated mercuric chloride solution for 5 min.
- Treating the soil with pentachloroni trobenzene at the rate of 70 kg/ ha lowers the incidence of the disease, but it is too expensive and cumbersome.
- Well, sporulated tubers may be planted shallow to control the disease.
- The disease severity is reduced in the land is left fallow for 2 years.
