Marssonina Blotch disease is caused by Marssonina Coronaria. It is one of the most serious disease of apple in India. All the commercial varieties of apple are susceptible to this disease. The main damage caused by Marssonina Blotch is premature defoliation of apple trees with fruit still hanging on the tree. The pathogen causes dark spots on both the leaves and fruit, which may weaken the trees.
The disease usually starts in rainy summers with grey-black spots on the upper side of the leaves. These spots develop into larger spotted areas surrounded by red edges. The numerous spots turn the leaf yellow and prematurely fall off the tree. Defoliation starts approximately after two weeks of the first symptom. Severe defoliation reduces the quantity and quality of apples, and sometimes affects flower initiation in autumn, leading to reductions in fruit set in the following season. As such no symptoms are seen on the fruit but can be seen rarely in heavily infected orchards.
Proper sanitation is required to keep away disease. The spores of the Marssonina Blotch can be destroyed by destroying the fallen leaves in autumn.
Marssonina Blotch infection starts 50 days after full bloom. No need to do any sprays for Marssonina Blotch before 50 days after bloom. For Marssonina, Preventive sprays are often more useful than curative sprays. If weather remains dry spraying after 20 days interval helps and if weather remains humid or rainy, sprays are considered after every 12 days.
Protective sprays of fungicides provide significant reduction in disease incidence of Marssonina Blotch. Fungicides that are highly effective and exhibit maximum disease control are—
- Copper Oxychloride (post harvest application only)
Fungicides used in combinations are also seems effective and decrease possibilities of increase in pest resistance .
- Dodine plus Hexaconazole
- Zineb plus Hexaconazole
- Mancozeb plus Carbendazim
- Fluopyram plus Pyrachlostrobrin
- Metiram plus Pyrachlostrobrin
- Tebuconazole plus Trifloxystrobin
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