Effect of measured levels of Sigatoka disease of bananas on fruit quality and leaf senescence
AbstractOn termination of Sigatoka control measures, from four to eight month were required for premature ripening to appear depending on the amount of spotting present at the time spraying was stopped and the sea on of the year. When the average age of the youngest leaf with spots was younger than leaf No.9 and when more than 50 per cent of the spotted plants had leaves younger than No. 8 spotted, premature ripening appeared within four to five months. When spraying was resumed with benomyl it required about 2·5 months to eliminate premature ripening. Ripening was normal from 1 to 1·5 months after the average age of the youngest leaf spotted was less than No. 9 and less than 20 per cent of the spotted plants had leaves younger than No. 8 spotted. Premature ripening can occur at spotting levels that do not affect stem weight. However, with increasing amounts of potting, stem weights are reduced and most stems ripen or soften in the field before reaching harvesting grade. There was no difference in number of days from flowering to harvest between normal stems and stems that ripened prematurely except at very high levels of spotting. Then there was a difference in age of only two to three days between normal stems and stems that ripened prematurely in the field. Leaves with spotting senesced, as indicated by rate of petiole collapse, up to 25 per cent more rapidly than non-spotted leaves. Depending on the intensity of spotting there were from one to three fewer leaves present at harvest as a result of Sigatoka infection. Premature ripening did not occur under the following leaf spot levels: average age youngest leaf spotted-not younger than leaf No. 9; percentage of plants spotted with leaves younger than No. 8-not more than 20; percentage of medium sized non-flowered plants spotted-not more than 60. These levels are proposed as the minimum standards for Sigatoka control that prevent premature ripening in Central America.