Violet Root Rot
Violet root rot is caused by the fungus, Sphaerostilbe repens B& Br. Violet root rot attacks all tea plants above one year old in waterlogged areas.But the characteristic symptoms are produced on plants of about two years and above.
Affected roots are inky black or light violet in colour and freshly dug up ones often smell sour or vinegary.The surface of the wood is covered with thick, irregular white to orange flattened strands of mycelia that ultimately changes to purplish black. Fructifications may either look like small groups of pinkish or orange coloured pins (about 3mm long) with white heads on root surface or a cluster of minute red to black flower bud like bodies at collar region or little above.
Affected bushes bear leathery and yellowish leaves and carry few plucking points, become unproductive and finally die.
The disease caused by the fungus, Botryodiplodia theobromae (Pat.) may attack any part of the tea plant, young or old, only when the plant is debilitated by other causes. When the root is attacked, no characteristic symptom develops initially. However, in advanced stages small isolated or groups of greyish black to coal black hairy cushions develop, giving a shooty appearance which may extend upto collar. The wood when sliced, exhibit even bluish black discoloration.
Infection is believed to take place through air borne spores.
The fungus Rhizoctonia bataticola (Tank)or Macrophomina phaseoli attacks all tea plants, young and old, when they are debilitated by other causes as does Diplodia. Very often Rhizoctonia and Diplodia diseases occur together since their attack is favoured by the same conditions.
No outward symptom in the affected roots is visible. On the surface of the wood beneath the bark and also in the wood number of minute, irregular black dots (sclerotia) are noticeable, Rhizoctonia infested roots are very light in weight and completely devoid of reserve.