STRATEGIES TO CURTAIL FUNGAL DISEASES

 IN CARDAMOM PLANTATIONS

 

Praveena, R., Biju, C.N. and Ankegowda, S.J.

Indian Institute of Spices Research,

Cardamom Research Centre, Appangala,

Heravanadu Post, Madikeri 571 201

Karnataka

 

The serenity of unblemished cardamom plants vividly coloured in green shade bathed in golden rays filtering through the canopy of shade trees is certainly a feast for eyes. However, for centuries, the enchanting queen of spices clan is waging unrelenting battles against a battalion of pathogenic microbes, having the potential to steal away the picturesque of cardamom tracts. The microclimatic conditions prevailing in the cardamom ecosystem often favours these unsolicited intruders to proliferate and inflict damage to the plants. Cardamom suffers from the attack of various pathogenic microbial agents, of which diseases caused by fungi are of major concern. The disease induced by these organisms often attains severe proportions in nurseries and in plantations, where adequate crop protection measures are seldom adopted.

In primary nurseries, leaf spot caused by the fungus Phyllosticta elettariae is a destructive disease and appears mostly during February- April months with the receipt of summer showers. The disease manifests as small circular or oval spots, which are dull white in colour. These spots later become necrotic and leave a hole (shot hole) in the center of the affected portion (Fig.1).

In secondary nurseries, another type of leaf spot caused by Cercospora zingiberi is of common occurrence. The symptoms appear as yellowish to reddish brown coloured rectangular patches on the lamina, almost parallel to the side veins. In the later stages lesions colour of the lesions turns to muddy red.

 

Damping off or seedling rot usually appears in the primary nurseries during the monsoon season, when there is excessive soil moisture due to inadequate drainage. The disease is caused by soil borne fungi, Pythium vexans and Rhizoctonia solani and the incidence varies from 10 to 60 per cent. In severe cases, the seedlings wither and collapse in masses.

DISEASE MANAGEMENT IN NURSERY

·         Practice of raising nurseries regularly in the same site should be avoided.

·         Cardamom seeds should be sown in the month of August – September, to ensure sufficient growth of seedlings, so that seedlings develop sufficient tolerance to the disease.

·         In primary nurseries, thin sowing may be practiced to avoid overcrowding of seedlings.

·         Wherever required, provide adequate drainage facilities in primary and secondary nurseries.

·         Cardamom seedlings affected with damping off should be removed and proper phytosanitary measures should be practiced in the nurseries.

·         When leaf spot incidence is observed, spray carbendazim (Bavistin) @ 0.2 per cent on the leaves at fortnightly intervals. Two to three rounds of spraying may be undertaken depending on the intensity of the disease.

·          On initiation of damping off, drench the nursery beds with copper oxychloride (COC) (0.2 per cent) @ three to five liters per square meter. Two to three rounds of COC drenching may be resorted at 15 days interval, depending on the severity of the disease.

In cardamom plantations, capsule rot/Azhukal and clump rot were reported to be the most important fungal diseases. However, in the recent past incidence of several minor diseases are increasing resulting in a setback in the production and productivity of cardamom.

 

AZHUKAL OR CAPSULE ROT

 ‘Azhukal’ is a serious problem in cardamom plantations and is  a major constraint in the successful cultivation of cardamom in Kerala and elsewhere. The disease is caused by Phytophthora nicotianae var. nicotianae and P. meadii. During heavy and incessant rainfall conditions, crop loss as high as 40 per cent occurs.

 

The disease appears in the form of water soaked lesions on tender leaves and capsules. On the leaves, water soaked lesions later turns necrotic, surrounded by yellow halo. In advanced stages, the leaves rot and shred along the veins. Finally, the affected leaves break at the base of petiole and remain hanging. Plants of all ages are susceptible to the disease. However, under field conditions disease incidence is noticed mainly on the bearing plants. Infection on immature capsules results in rotting which emit a foul smell and later, fall off (Fig.2). Mature capsules when infected, become shriveled up on drying.

The disease attains maximum severity during the months of heavy and continuous rainfall which facilitates build up of high relative humidity, especially during July. Heavy shade and closer spacing coupled with favourable weather conditions predispose the plants to infection.

MANAGEMENT

·         Trashing and destruction of the infected parts should be done as a phytosanitary measure prior to the onset of southwest monsoon (May).

·         The dried leaves and leaf sheaths from the basal region of the plant should be removed to the maximum extent possible.

·         Thick shade may be regulated by gentle lopping of branches of the shade trees.

·          In plantations, wherever water stagnation is a problem, adequate drainage should be ensured. 

·         Prophylactic sprays with Bordeaux mixture (one  per cent) should be given during May-June and subsequent sprays may be undertaken during July –August. If the monsoon prolongs, a third spray may be given during September.

·         When the disease makes it appearance Fosetyl-Al (Aliette ) 0.2 per cent or potassium phosphonate (Akomin) 0.5 per cent can be sprayed @ 500-750 ml per plant.

·         Drenching of plant basins with 0.2 per cent copper oxychloride (COC) reduces soil inoculums levels and prevents further spread of the disease.

·         Application of potential antagonistic fungal agents like Trichoderma viride or T. harzianum mass multiplied on suitable carrier media to the plant basins @ 1kg during May and September –October further helps in checking soil borne diseases. If the soil is drenched with COC or other fungicides, Trichoderma should be applied only after 15 days.

 RHIZOME ROT

 

Rhizome rot also known as clump rot is one of the earliest reported fungal diseases in cardamom.  Soil borne pathogenic fungi such as, Pythium vexans,  Rhizoctonia solani and Fusarium sp. are the causal organisms .The disease initially manifests as yellowing of foliage, followed by drooping of leaves. The collar region becomes brittle and breaks off at slight disturbance. As the disease advances, rotting extends to the rhizomes as well as roots and the affected tillers subsequently fall off (Fig.3) . Rotten rhizomes become soft, dark brown coloured and emit a foul smell. Lodging of tillers due to rhizome rot diseases is severe during the monsoon season.

 

MANAGEMENT

 

·         Phytosanitary measures as recommended in the Azhukal disease may be practiced.

·         Once the disease appears in the plantations, basins of the cardamom plants should be drenched with two to three liters of COC (0.2 per cent). Drenching of COC may be repeated at 30 days interval for two to three times depending on severity of the disease.

·         Application of Trichoderma culture multiplied on a suitable substrate helps in promoting growth of the plants as well as checking the disease development.

 

LEAF BLIGHT

In recent years, leaf blight popularly known as Chenthal caused by Colletotrichum gloeosporioides gained considerable importance. The disease which appears during mid- monsoon, becomes severe during late monsoon periods (October-November) and declines by March. The symptoms initially manifests on the leaves as yellow lesions which later elongate to form necrotic streaks that run parallel to the veins. Several such lesions later coalesce to form yellowish-brown to reddish-brown patches, which subsequently withers off (Fig. 4). In the advanced stages of disease development, several such lesions develops on both young as well as older leaves which eventually dries up and gives a burnt appearance to the affected plants. Intermittent rains and prevalence of misty conditions in the plantations favours the incidence and spread of the disease.

 

MANAGEMENT

 

            Timely and meticulous adoption of recommended cultural practices and plant protection measures reduces the incidence of leaf blight to a considerable extent.

·         Leaf blight affected portions should be destroyed during May, before the onset of monsoon.

·         The disease is more severe under exposed conditions, due to poor adoption of shade regulation practices. Intensity of the disease can be reduced significantly by providing adequate shade in the plantations. It is appropriate to regulate shade before the onset of South –West monsoon season. Optimum shade levels may be maintained in the plantations by allowing upto 40-60 per cent filtered light.

·          As a prophylactic measure, Bordeaux mixture (one per cent) @ 500 ml to one liter /plant should be sprayed during May – June before the onset of monsoon, which may be repeated during the months of August- September.

·         Once leaf blight appears in the field, fungicide sprays with the combination product of carbendazim and mancozeb (Companion) 0.1 per cent or carbendazim (Bavistin) 0.2 per cent @ 500 - 750 ml/plant may be adopted. Spraying should be undertaken during August-September which may be repeated for two to three times at an interval of 30 days depending on the severity and extent of damage. Adequate care should be taken that the entire foliar portion is covered with the spray solution.

 

LEAF BLOTCH

 

Leaf blotch, comparatively less important disease is caused by Phaeodactylium alpiniae. During monsoon season, lesions develop at the tip or near the leaf midribs which subsequently turns to brownish necrotic patches. The mycelia and conidial masses of the fungus are visible as thick grey coloured mats or powdery coatings on the underside of the blotched area. During dry weather conditions infection is restricted to smaller lesions and spread of the disease in plantations is also limited. The disease can be managed by adopting foliar sprays with Bordeaux mixture (one per cent), copper oxychloride (0.2 per cent) or mancozeb (0.3 per cent).

 

STEM LODGING

 

 The disease mainly affects the tillers and widely distributed in the cardamom plantations in Idukki district of Kerala and lower Pulney Hills of Tamil Nadu. The disease is incited by Fusarium oxysporum and the disease appears commonly during the post-monsoon periods

 The disease is characterized by the formation of pale discoloured patches on the middle portion of the tillers, which lead to dry rot. As a result of the infection, the tillers become weak and break off at the point of infection. The partially broken tillers bend downwards and hang from the point of breakage (Fig. 5). When the infection occurs at the collar region, the tillers fall of giving a lodged appearance. In the affected tiller leaves and leaf sheaths dries off. Spraying with Bavistin (0.2 per cent) or Hexaconazole (Contaf) 0.2 per centcan manage the disease.

 

ROOT TIP ROT

The disease makes its appearance during post monsoon season and attains severity during summer. The symptom includes rotting of the root tips followed by die back of roots (Fig. 6). The lower leaf of affected tillers become yellowish and gradually dries off. The disease is caused by Fusarium oxysporum . Spraying and drenching plant basins with carbendazim (Bavistin) 0.2 per cent or hexaconazole (Contaf) 0.2 per cent are recommended and the application may be repeated at 15- 20 days interval for effective management of the disease.