| Large cardamom (Amomum subulatum Roxb.) is shade loving crop and is grown under humid and cool conditions. Sikkim has largest area under the crop in India. The crop ia affected by various fungal and virus diseases. 1. LEAF STREAKSymptoms:
- The symptoms of leaf streak are characterized by the presence of numerous elongated translucent streaks on young leaves along the veins.
- Within 3-4 days the streaks turn reddish brown and develop a straw coloured necrotic area in the centre which is surrounded by prominent dark brown margins.
Disease cycle and epidemiology
- Leaf streak is caused by Pestalotiopsis royenae(D.Sacc.) Steyaeri.
- Accervuli are dark brown to black.
- Conidia are multiseptate, usually 5-celled, three median ones are brown and two end ones are hyaline, having simple or branched appendages.
- Cool and moist weather favours the disease.
- Pathogen overwinters in the form of acervuli or dormant mycelium.
i) The glosey variety, with a crinkled leaf pattern is more susceptible to the pathogen than the Sawney variety, which has smooth leaves.2. RUSTSymptoms:
ii) Fungicides like carbendazim (0.1%), zineb (0.25%) are effective.
- The disease is mostly observed during May and June on the lower surface of leaves in the form of minute, brown uredosori (Plate-3).
- The numerous uredosori are surrounded by chlorotic halos during early stages of development.
- In severe cases, the whole leaf gets covered by uredosori resulting in premature drying.
- The disease is caused by Phakopsora elettariae (Racib.) Cummins.
- Uredospores sessile, obovoid to ellipsoidal, echinulate, yellowish brown and become cinnamon brown with age.
- Teliospores one-celled, erragularly arranged in 2-7 layers, oblong to ellipsoidal.
3. LEAF SPOT AND BLIGHTSymptoms:
- Spray the crop with mancozeb (0.25%) or tebuconazole (0.05%) and repeat after 10 to 15 days interval
- The disease is recorded around Gangtok causing heavy foliage damage.
- Minute grey spots with chlorotic haloes develop on the leaves mostly from the tips of margins (Plate-4).
- The spots are irregular in shape, with a prominent reddish brown margin surrounded by chlorotic holes and the central portion becomes necrotic.
- Several such spots often coalesce and give a blighted appearance to the foliage.
- The disease is caused by Pestalotiopsis versicolor (Speg.) Steyaert.
- Pathogen forms dark brown to black erumpent acervuli.
- Conidia are fusiform, four septate with apical and basal appendages.
- The disease is prevalent during April to September.
- Minute brown spots appear on the leaves initially which expand very fast during rainy season.
- A typical spot is generally elliptical upto 5 X 4 cm in size with greyish white centre, brown margins and surrounded by a chlorotic halo.
- The black acervuli arranged concentrically in greyish white portion of the spots, can be seen by the naked eye.
- The spots are more conspicuous on the upper surface.
- The spots coalesce and the entire leaf blade either dries up in winter or rots during rainy season. Perithecia are found in dry leaves.
Disease cycle and epidemiology:
- The disease is caused by Glomerella cingulata (Stons.) Spauld &Schrenk (Ann. Colletotrichum gloeosporioide(Penz.)Penz. & Sacc.
- Ascomata single or in groups mostly immersed in host tissue.
- Ascospores small, hyaline.
- Conidia straight and cylindrical.
- The pathogen overwinters in the form of mycelium in the plant debris. Conidia are produced in acervuli.
- High humidity along with moderate temperature favour the disease.
- Collect and destroy the infected plant debris.
- Spray the crop with carbendazim (0.1%) singly or in combination with mancozeb (0.25%)
- This is one of the important diseases of large cardamom in nursery and field.
- Maximum damage to the nursery occurs in February and March.
- The intensity of the disease is severe in plantations from October to February.
- Sudden wilting of the plant or individual leaf is the characteristic symptom of the disease.
- The first symptom is chlorosis of the older leaves at the junction of petiole with pseudostem.Chlorosis begins at the base of the petiole of one or two of the older leaves and progresses to the younger ones.
- The emerging heart leaf commonly shows necrosis and the base of the pseudostem may split.
- All the leaves eventually collapse leaving the pseudostem exposed.
- Brown to black vascular discolouration is seen in the outer leaf sheath throughout the pseudostem.
- The roots show blackening and the bark is peeled off easily.
- Finally the whole clump dries up.
6. SPIKE ROT, ROOT ROT AND COLLAR ROTSymptoms:
- The disease is caused by Fusarium oxysporum (Schlech. ex. Fr.).
- Pathogen and disease cycle and management are explained in tomato diseases chapter
- The initial symptoms appear as water-soaked areas with purple brown margins on calyx or corolla.
- The infection extends very fast and results in complete rotting of flowers and failure to form capsules.
- The whole spike becomes slimy, soft and watery.
- Yellowing of seedlings is the main symptom of the disease in the nurseries while the pseudostems are attacked near the ground level.
- The affected portion becomes constricted, watery and soft as a result of which seedlings collapse.
- Roots of affected seedlings are destroyed completely.
- The disease is caused by Rhizoctonia solani Kuhn.
- Pathogen, disease cycle and epidemiology are explained in potato diseases.
- Rouging of plants, field sanitation, proper drainage, removal of diseased plant debris and weeds are effective in reducing the disease.
- Before the onset of monsoon drench and spray with carbendazim (0.1%) or Bordeaux mixture (4:4:50) or mancozeb (0.25%).
VIRAL DISEASES7. CHIRKEYSymptoms:
- This is a major disease of large cardamom.
- The disease spreads rapidly and the symptoms can not be identified unless closely observed.
- In young leaves, discrete pale green to yellow longitudinal stripes running parallel to each other cab be seen, but in mature leaves, the symptoms are masked.
- The flecks measures 2.5 mm and the characteristic mosaic symptoms are also seen.
- The affected plants produce flowers and spikes but without capsules.
Disease cycle and epidemiology
- The disease is caused by a virus.
- The corn aphid Ropholosiphum maydis is the vector for the disease.
- The disease is also spread by planting infected suckers.
- Removal of volunteers .
- Use healthy planting material.
- Control aphid vectors.
- The foorkey disease was first reported by Vasudeva in 1956.
- It causes severe damage in Darjeeling district of West Bengal.
- The symptoms of the disease are production of bushy growth of stunted shoots which are sterile.
Disease cycle and epidemiology:
- Disease is caused by a virus.
- Virus particles are 32 nm in diameter.
- Ttransmitted through banana aphid Pentalonia nigronervosa.
- Diseased plants survive for few years but remain sterile and unproductive.
- Infected plants should be uprooted and the surrounding are drenched with systemic insecticides to control movement of aphids on the main host as well as collateral hosts such as corn, banana, peach and squash.
- The plantation should be regularly sprayed once in three weeks with metasystox to check the movement of aphids.