Diseases of Tea
Blister blight – Exobasidium vexans
- Small pale or pinkish circular spots appear on leaves and attain a size of 2.5 cm diameter.
- The spots in the upper surface of the leaf becomes light brown in color and depressed while in under surface of leaf it bulges farming a blister like swelling.
- Lower budget portion is covered with a white powdery growth of fungus.
- When many spots coursers, curling of leaves will occur.
- When it spreads to young succulent stems affected portion are withered.
- The leaf yield is reduced vigor of the tea bush is affected.
- The mycelium is confined to the blistered areas on the leaves.
- They are septae and collect in bundles below the lower epidermis.
- Later by rupturing the epidermisa continuous layer of vertical hyphae are projected on the surface of spot.
- The fungus produces two kind of spores viz.,the conidia and basidiospores.
- The conidia are most abundant, borne singly at the tip of long stalks.
- Basidia are formed on the surface in large number but never form a continuous hymenium.
Mode of spread and survival
- The fungus completes its life cycle in 11-28 days and several generations of spores are produced in a season.
- It produces conidia and basidiospores in the same blister.
- Spores are air borne.
- The perpetuation of the fungus appears to be form the pre existing infected bushes.
- Removal and destruction of the affected portion.
- Spraying with Copper oxychloride 0.25 % in effective.
- Spray with 210 g of COC + 210 g nickel chloride/ha at 5 days interval from June – September and 11 days interval in October – November gives economic control.
- Spraying with systemic insecticides like Atemi 50 SL at 400 ml/ha (or) Baycor (300 EC) at 340 ml/ha a weekly interval is also effective.
- Chlorotalonil, Bayleton, tridemorph is also effective.
- Tridemorph at 340 and 60 ml/ha is satin factory under mild and moderate rainfall condition.
- Small dark brown irregular spots appear on leaf.
- They coalesce to produce a dark brown patch which eventually covers the whole leaf and drop off.
- Before the leaf turns black the lower surface assumes a white powdery appearance.
- Corticium invisum and C. theae
Mode of spread and Survival
- Basidiospores carried by workers.
- The disease develops rapidly when temperature is high and air is humid.
- At the beginning of rainfall they germinate and produce hyphae which start fresh infection.
- Occur in nursery shaded with Crotalaria.
- Basidiospores germinate only in wet weather or when leaves are covered with dew.
- Prune in December end, remove the prunings immediately, burn after drying.
- Collect all dead and dried leaves.
- Spray a copper fungide in third week of April.
Red rust: Cephaleurus mycoidea
- Orange yellow, circular patches appear on upper surface of leaves.
- The spots become brown and dry up.
- When it affects the given stem it hardens prematurely.
- Cephaleurus mycoidea also attacks Tephrosia sp. and Desmodium gyroides grown as green manure and shade.
- Rainy season is best suited for propagation of algae.
- Removal of infected portion and spraying with Copper oxychloride 0.25 %
Black root: Rosellina areuata
- The fungus originate from the dead heaped leaves of 5 – 7.5 above the soil level.
- From there if spreads to roots region of tea bushes.
- When bark is removed star like growth of mycelium can be seen.
- At the surface of the soil the mycelium surrounds the stem and kills the bank for the length of 7.5 – 10.0 cm.
- A swollen ring of tissue is formed round the stem above the dead patch.
- The fungus produces two kinds of fructification, a conidial stage and a perithecial stage.
- The conidia are borne on short bristle like stalks.
- The perithecia are black and spherical.
- They bear asci which in turn bear ascospores.
Mode of spread
- The disease is spread by wind
- Removal and destruction of infected plant.
- Clean cultivation with out fallen leaves.
- Dig a drench around the infected bush to provide sunlight in the drench which prevent the spread of mycelium.