Sigatoka leaf spot is a serious disease of banana that destroys large areas of plantations resulting in severe reduction in fruit yield.
The commercial cultivars nendran and robusta are highly susceptible to this infestation whereas in rasthali and palayankodan varieties the disease severity is less.
This infestation is caused by a fungus and was first recorded in the Sigatoka valley of Fiji. Economic losses of 50-100 per cent have been incurred due to the incidence of this disease.
Dark brown spots
Symptoms of Sigatoka disease first appear as small dark brown spots or lines on the underside of third or fourth opened leaf. The spots become sunken surrounded by a yellow halo. Eventually these spots or streaks expand and become brown or black and make a characteristic black patch on the leaves.
The infection gives a scorched appearance to the foliage. Infection on younger leaves is more severe causing them to dry up more quickly. Appreciable fruit loss occurs as there is drastic reduction of leaf surface area for photosynthesis.
Infected banana plants produce fruits of inferior quality as the banana fingers produced do not develop properly and remain small and thin.
Spores of the fungal pathogen form in abundance during tropical and sub tropical summers along with intermittent rainfall especially if there is a film of water on the leaves.
The principal means of spread is through rain but later with the progressive development, spores are also discharged through air currents.
Spotting of leaves starts to increase during June, July, peaks in October-November and remains at a high level through December.
Management mainly involves chemical control using fungicides like copper oxychloride, mancozeb, chlorothalonil or carbendazim at the prescribed dosage.
Fungicide spraying on the foliage and pseudostem should be commenced with the initial appearance and repeated at two weeks’ interval. Use of the different fungicides in rotation will reduce the risk of resistance development in the pathogen to the systemic chemicals.
(Dattatray L. Shinde, PG students plant pathology and Prof. Kamala Nayar, College of Agriculture, Vellayani, email: firstname.lastname@example.org, phone: 0471- 2383573)