The crop is susceptible to a number of diseases, which are mainly viral and fungal in origin. Large cardamom productivity is affected seriously by viral diseases. However fungal diseases are not major constraints. There are two viral diseases on large cardamom causing severe damage to the plantations. Chirke is serious as far as rate of spread is concerned; Foorkey is serious as far as yield loss is concerned. Among fungal diseases, flower rot, clump rot, leaf streak and wilt are known to cause damage to the plant and ultimately reduce the crop yield.
This virus disease is characterized by mosaic with pale streak on the leaves. The streaks turn pale brown resulting in drying and withering of leaves and plants. The flowering in diseased plants is extensively reduced and only one to five flowers develop in one inflorescence, as against 16–20 in an inflorescence of healthy plants () and by the end of third year of crop the loss is around 85 per cent. The cultivar Kopringe is resistant to chirke while the perennial weed, Acorus calamus L. was found to be highly susceptible (). The disease is readily transmitted by mechanical sap inoculation and in field it is spread by aphids, Rhopalosiphum maidis Fitch., within a short acquisition feeding period of 5 min.
Primary spread of diseases from one area to another area is through infected rhizomes and further spread within the field is by aphids (). Rapid serological method was developed to locate chirke diseased plants under field condition in the manner as described by Bradley and Munro ().
This disease is characterized by dwarf tillers with small, slightly curled pale green leaves. The virus (spherical particles of 37 nm diameter) induces remarkable reduction in size of leafy shoots and leaves of the infected plants and also stimulates proliferation of large number of stunted shoots arising from the rhizome. The spikes/inflorescence are transformed into leafy vegetative parts and fruit formation is altogether suppressed. The diseased plants remain unproductive and gradually degenerate. Foorkey symptom appears both on seedlings and grown up plants ().
Unlike Chirke, Foorkey virus is not transmitted through sap but by the aphids Pentalonia nigronervosa Cog. and Micromyzus kalimpongensis Basu (). The primary spread of disease from one area to another is through infected rhizomes and further spread within the plantation by aphids. Infected rhizomes can be killed by injecting Agroxone-40.
Management of chirke and foorkey
The following methods are adopted to considerably minimize these two viral diseases in the affected plantations ():
(i) Regular rouging of diseased plants, if any.
(ii) The diseased plants are uprooted and destroyed as and when they are traced.
(iii) Uprooted plants are taken to an isolated place, chopped into small pieces buried in deep pits for their quick decomposition.
(a) Use of healthy and disease free planting materials preferably seedlings; (b) suckers as planting material from diseased area are avoided for replanting and (c) raising nurseries in the vicinity of infected plantations are avoided.
Leaf streak disease
It is a fungal disease caused by Pestalotiopsis royenae (D. Sacc) Steyaert., and is a serious disease among foliar diseases and is prevalent round the year. The disease symptom is the formation of numerous translucent streaks on young leaves along the veins. The infection starts from emerging folded leaves; infected leaves eventually dry up causing loss of green part and reduce the yielding capacity of the plant. Dzongu Golsey is found more susceptible to leaf streak ().
Three rounds of 0.2 per cent spray of copper oxychloride at 15 days interval, two schedules in a year i.e. February–March and September–October can control this disease.
A fungal disease caused by Fusarium and Rhizoctonia sp. The affected flowers turn dark brown and fail to develop into capsules, if infection takes place before or at the time of fertilization. If infection occurs after flowering or during fruit set, the affected fruit or capsule loses color and odor (). The disease can be managed by avoiding: (a) accumulation of leaf mass or mulch over the inflorescence/spike during rainy season and, (b) soil spills over spikes.
A fungal disease caused by Fusarium oxysporum is prevalent in swampy and open areas. Early symptom is chlorosis of the older leaves commencing from the petiole region and progressing inwardly towards the young leaves. As the infection progresses, the pseudostem also gets rotten, thereby blocking the vascular bundles, and pseudostem is collapsed as the infection progresses. Ultimately the plant dries up.
Drenching 0.5 per cent Dithane M-45 or Thiram would help in checking further spread of disease in nurseries as well as in main plantation. Planting in swampy or dry area should be avoided.
Selections from the book: “Cardamom. The genus Elettaria”. Edited by P.N. Ravindran and K.J. Madhusoodanan. Series: “Medicinal and Aromatic Plants — Industrial Profiles”. 2002.