Importance of Sigatoka leaf spots

The spread of black Sigatoka to Africa and the American tropics within the last 25 years has made the disease the most economically important disease of bananas and plantains. Although bananas are severely defoliated by Sigatoka diseases, they are not usually killed unless infection is heavy on a highly susceptible cultivar. However, a good level of disease control is essential for export fruit, as fruit from affected plants tends to ripen prematurely (Ramsey, et al., 1990). Where the disease is not controlled, the leaves senesce faster decreasing the functional leaf area and thus decreasing yields. In addition, yield is reduced in areas with both types of Sigatoka leaf spot, as it can become necessary to harvest fruit at a lower grade (i.e. younger) in order to lessen the chances of premature ripening of the fruit in transit (Stover, 1974; Stover & Simmonds, 1987).

The cost of black Sigatoka control has been estimated as approximately three to six times greater than for yellow Sigatoka. For example in Honduras in 1984, black Sigatoka control was approximately 26% of the cost of producing a box of bananas, and was reported to reduce the yield of commercially-grown 'Horn' plantains (Musa AAB) by 50% (Stover & Simmonds, 1987). In Costa Rica in the 1980s, the cost of control measures for black Sigatoka alone was estimated at approximately US$ 17.5 million/year, and the estimated cost of black Sigatoka control in Central America, Colombia and Mexico from detection until 1985 was over US $350 million (Stover & Simmonds, 1987).