Studies on Premature Leaf Fall in Apple - a New Problem

In last few years, apple plantations in Himachal Pradesh were severely affected by an early leaf drop. The disease appears invariably after the onset of rainy season and is characterized by sudden defoliation following yellowing of older leaves in lower portion of trees with or without necrotic lesions. The leaves in upper portion of trees which escape immediate fall develop necrosis turning ash grey, late in the season. In 1996, the effect was so severe in some orchardsthat only fruits were left on thetreeswithoutfoliage. The orchards located in the valley areas, along the rivulets and shady locations were the worst affected. At first, Golden Delicious appeared to be the most susceptible cultivar but further observations revealed almost similar susceptibility in all the test Delicious cultivars. Disease incidence, however, varied from orchard to orchard and even within the same orchard. Well managed orchards were less affected and some of them were totallyfree from this malady. Trees treated with mancozeb, propineb and carbendazim had very less leaf drop, whereas other fungicides hexaconazole and captan did not inhibit the problem significantly. No fungal infection was apparent in the leaves dropped in early season. However, fruiting bodies of Marssonina sp. were found in ash coloured necrotic portions of the later affected leaves.