Major Castor diseases are given below:-
1.Castor Seedling Blight: Phytophthora colocasiae
- The disease first makes its appearance on both the surfaces of the cotyledonary leaves in the form of a roundish patch of dull green colour which soon spreads to the point of attachment causing the leaf to rot and hang down.
Spot on older leaf
- The infection further spreads to the stem with the result that the seedling is killed either due to the destruction of growing point or by the collapse of the stem.
- The true leaves of seedlings and the very young leaves of older plants may also be affected, but ordinarily, not much injury is caused.
- The leaf spots turn yellow and then brown and concentric zones of lighter and darker brown colour are formed.
- The disease spots coalesce at a later stage and cover almost the entire leaf.
- The affected leaves shed prematurely. Under moist conditions, a very fine whitish haze is found on the under-surface of the leaf spots.
- In the case of mature plants also the disease may spread from young leaves to the stem through the petiole.
- It will be drained, damp and low lying localities should be avoided for sowing castor.
- Seed dressing with 4g Trichoderma viride formulation on 3g Metalaxyl per kg seed can reduce disease incidence.
- Soil drenching with Copper oxychloride @3g /lit or Metalaxyl 2g/lit.
2.Castor Alternaria Blight: Alternaria ricini
- All the aerial parts of the plant, i.e., stem, leaves, inflorescence and capsules are liable to be attacked.
- These may appear on any portion of the leaf and are irregular, scattered, and have concentric rings.
- These are brown and later become covered with bluish-green or sooty growth.
- When the attack is severe the spots coalesce and form big patches resulting in premature defoliation of the plant which gradually wilts away.
- In one case the capsules, when half mature, wilt suddenly, turn brown and due to the collapse of the pedicel the capsules fall or hand down.
- They are smaller in size and have under developed and wrinkled seeds with little oil content.
- Seed treatment may be useful in combating the initial phase of the disease.
- Use of healthy seed and treat the seed with Captan or Thiram @ 4g/kg seed or spray Mancozeb at 2.5g/lit concentration at an interval of 15days commencing from 90days of crop growth.
3.Castor Cercospora Leaf Spot: Cercospora ricinella
Spots on leaf
- The disease appears as minute black or brown points surrounded by a pale green ring.
- These spots are visible on both the surfaces of the leaf.
- As the spots enlarge, the centre turns pale brown and then greyish-white surrounded by a deep brown band which may be narrow and sharp or broad and diffused.
- The fructifications of the fungus appear as tiny black dots in the white centre.
- The diseased spots often occur in great numbers scattered over the leaf and are roundish when young but may become irregularly angular when mature.
- When the spots are close together, the intervening leaf tissue withers and large brown patches of dried leaf may result
- Spraying with Mancozeb 0.25%
- Spraying twice with Mancozeb 2.5g/lit at 10-15 day interval reduces the disease incidence.
- Treat the seed with Thiram or Captan 4g/kg seed.
4.Castor Powdery Mildew: Leveillula taurica
Powdery mass covering entire leaf
- It is characterised by typical mildew growth which is generally confined to the under-surface of the leaf.
- When the infection is severe the upper-surface is also covered by the whitish growth of the fungus.
- Light green patches, corresponding to the diseased areas on the under surface, are visible on the upper side especially when the leaves are held against the light.
- When the weather is comparatively dry spray twice Wettable Sulphur 3g/lit at 15 days interval, starting from 3 months after sowing.
- Spray 1ml Hexaconazole or 2ml Dinocap /lit of water at fortnight intervals. The variety Jwala is resistant to this disease.
5.Castor Wilt: Fusarium oxysporum
- Leaves are droop and drop off leaving behind only top leaves.
- Diseased plants are sickly in appearance.
- Wilting of plants, root degeneration, collar rot, drooping of leaves and necrosis of affected tissue and finally leading to the death of plants.
- Necrosis of leaves starts from margins spreading to interveinal areas and finally to the whole leaf.
- Split open stem shows brownish discolouration and white cottony growth of mycelia much prominently in the pith of the stem.
- Selection of disease free seed.
- Grow tolerant and resistant varieties like Jyothi, Jwala, GCH-4, DCH-30 and SHB 145.
- Burning of crop debris
- Green manuring and intercropping with red gram
- Treat the seed with Thiram @ 3g/ kg or Carbendazim @ 2g/ kg seed or with 4g Trichoderma viride formulation.
- Multiplication of 2.5 kg T.viride formulation by mixing in 50kg FYM, Sprinkling water and covering with polythene sheet for 15days and then applying between rows of the crops is helpful in reducing the incidence.
- TamilNadu Agritech Portal