1.AZHUKAL OR CAPSULE ROT
Azhukal, a Malayalam name which literally means rotting, is a serious disease of this crop and causes a crop loss upto 30 per cent.
Symptoms:
- During monsoon period, the disease appears on tender leaves and capsules as water-soaked lesions, which are surrounded by yellow halo and later on these lesions turn black and the tissues become dead.
- In advanced stages, the infection spreads to panicles and tillers.
- In extreme cases, the rhizomes also rot resulting into the death of the plant.
- Immature infected capsules rot and fall off emitting a foul smell but mature capsules become shriveled after infection.
- Pseudostems and roots are also infected.
Pathogen (s):
- Initially Phytophthora nicotianae (Barda de Hann) var. nicotianae Waterhouse was reported to be the causal agent of this disease.
- Later on, the involvement of Pythium vexans de Bary and also Phytophthora meadii McRae A2 mating type and Fusarium spp. have also been reported.
Disease cycle and epidemiology:
- The associated pathogen(s) are soil borne in nature and overwinter in the form of oospores or chlamydospores.
- Colocasia plants are reported to be the collateral hosts of P. meadii.
- Wet and humid weather conditions accompanied with low temperature prevailing in the plantations are highly favourable for the disease development.
- During August, the high rainfall and resultant increased relative humidity become the most congenial conditions for the disease development.
Management
i) Avoid movement of rhizomes from diseased area to disease free area for planting.
ii) Remove infected panicles and rhizomes.
iii) Improve drainage in the plantations.
iv) Soil amendment with neem cake has also been found effective (250 g/m2).
v) Biological control of P. meadii infections using antagonistic fungi like Trichoderma spp. and Laetisaria sp. has also been found effective.
vi) Application of fungicides like Bordeaux mixture (4:4:50) or copper oxychloride (0.3%) or metalaxyl + mancozeb (0.25%) or Aliette (0.3%) has been recommended.
2. RHIZOME ROT /ROOT ROT/DAMPING OFF
Rhizome rot is one of the oldest endemic fungal disease occurring in different parts of Kerala and Karnataka and is also called clump rot. The disease has also become increasingly important in nurseries causing damping-off. The disease incidence ranges from 9 to 60 per cent in different areas of Idukki.
Symptoms:
- The foliage of the infected plants becomes yellow followed by drooping of leaves.
- The infection is initiated at the collar region which becomes brittle and breaks off even at slight disturbance.
- As the disease advances, rotting of the collar region starts which extends to the rhizomes and roots and the affected tillers later fall off.
- Rhizome rot and shoot lodging is are severe during monsoon season.
- In seedlings, the damping off symptoms are produced and these die and collapse en masses.
Pathogen:
- Pythium vexans de Bary and Rhizoctonia solani Kuhn are the two fungi associated with rhizome rot while Fusarium oxysporum Schlecht.: Fr. is involved with seed and seedling rot.
Disease cycle and epidemiology:
- Pathogens responsible for this disease are soil borne and the apparently healthy seedlings from infected nurseries serve as the carrier of the inoculum to the main field.
- Poor drainage is considered as the main predisposing factor for disease initiation.
- Intensity of rainfall influences the disease development and more than 80 per cent infection occurs in between June-October.
- Nematode (Meloidogyne incognita) predisposes the seedlings to damping off or rhizome rot caused by Rhizoctonia solani.
Management
i) Roguing of infected plants in older plantations and change the site of nursery.
ii) Proper drainage.
iii) Apply pongamia cake (250g/m2) and Eupatorium leaves as mulch is useful in reducing the damping-off.
iv) Treat nursery bed soil with Formaline (5%) three weeks before transplanting.
v) Treat seed with carbendazim +thiram (0.25%) or carbendazim + captan (0.25%) or captan alone (0.4%) after treatment with nitric acid minimize seed rot incidence.
vi) With the initiation of the disease, spray the crop with the metalaxyl + mancozeb (0.25%) or Bordeaux mixture (4:4:50) and repeat at 10-12 days interval.
3. CHENTHAL OR BACTERIAL CANKER
This is a foliar disease and is locally known as Chenthal. Maximum reduction of 7-13 per cent in the yield has been noticed in Mysore variety.
Symptoms:
- Elongated water soaked lesions appear on the abaxial surface of young leaves.
- In advanced stages, the lesions become brown to dark brown with a pale yellow halo and the leaves wither resulting in wilting of pseudostems.
- The disease affected gardens present a burnt look.
- Flowers produced after disease appearance fail to form capsules.
Pathogen:
- Corynebacterium, a gram positive bacterium was reported as the causal organism.
- There are reports of association of Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. and Cercospora sp. also with the symptoms.
- After infection, the lesions develop in 12 h at temperature of 22-24o C at 90-95 per cent relative humidity.
Management
i) Weeds and ginger are collateral hosts and it is desirable to remove such weeds and avoid ginger cultivation.
ii) Provide adequate shade and use mulches to conserve moisture to reduce the disease.
iii) Spraying with Penicillin (0.01%) controls the disease. Spread of the disease can be checked by sprays of mancozeb (0.25%).
VIRAL DISEASES
4. MOSAIC OR KATTE DISEASE
The disease is locally known as Katte meaning a disorder and is known as marble disease in Anamalais. The disease is widely distributed in cardamom growing tracts of India with incidence ranging from 0.01 to 99 per cent. The infection of plants at the seedling stage leads to cent per cent losses in yield.
Symptoms:
- Slender chlorotic flecks measuring 2-5 mm in length appear on the youngest leaf of the affected tiller which later develop in to discontinuous pale green stripes which run parallel to the veins from the midrib to leaf margin (Plate-2 a &b).
- All new emerging leaves show characteristic mosaic symptoms with stripes of green tissue evenly distributed over the entire leaf lamina.
- Mosaic type of mottling is often seen on the leaf sheaths and young pseudo stems.
- The infection is systemic in nature and gradually spreads to all the tillers in a plant.
- In advanced stages, the affected plants produce shorter and slender tillers with few shorter panicles and degenerate gradually.
Pathogen:
- The disease is caused by Katte virus which have 650 x 10-12 nm homogenous flexuous particles and inclusion bodies.
Disease cycle and epidemiology:
- It is transmitted by banana aphid Pentalonia nigronervosa Coq.
- Clones from infected gardens, seedlings raised in the vicinity of infected plantations, voluntary seedlings collected from infected plants and few infected zingiberaceous hosts form the primary source of disease introduction to cardamom plantations.
- Entry of the virus also occurs in contiguous and nearby plantations upto 1000 m from the external inoculum source.
Management
i) Use healthy planting material which reduces the spread of the disease.
ii) Periodic surveillance of the plantations should be done at least twice a year to detect the virus infection and infected plants may be removed immediately.
5. KOKKE KANDU
The disease is of recent origin especially in cardamom growing pockets of Hassan, Coorg and Chickmagalur districts. The occurrence of the disease has also been reported from North Kanara in Karnataka. The incidence of the disease ranged from 10.4 to 42.8 per cent in Hongadahalla.
Symptoms:
- The first symptom of the disease is vein clearing which may be continuous or discontinuous and later these affected areas turn necrotic followed by shredding of lamina.
- All the new shoots are stunted with yellow mottling on pseudostems.
- Light yellow mottling is often clearly visible on panicles and capsules.
- Plants produce distorted leaves and capsules in advanced stages of infection.
- The new leaf gets entangled in the old leaf and forms characteristic hook like tillers and hence the name Kokke Kandu.
- Rossetting of leaves and cracking of capsules are also seen in advanced stages of infection.
- The newly infected plants show only faint discontinuous vein clearing symptoms with clear mottling symptoms on pseudostems in the summer months.
- The affected plants decline very rapidly and become stunted and perish within the same year of infection.
Pathogen:
- The disease is caused by a vein clearing virus. Successful transmission of the disease is obtained through cardamom aphid Pentalonia nigronervosa Coq., f. caladii.
Management:
- The affected plants should be destroyed.
- Since the infections are detected in nurseries located in the vicinity of affected plantations, it is imperative that the nursery sites may be selected away from such plantations.
Other diseases of importance are: Nilgiri Necrosis Disease (Virus).