Diseases:
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Powdery Mildew, Downy Mildew, Anthracnose.
Physiological disorders:
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uneven ripening, post-harvest berry drop, flower-bud and flower drop and pink berry formation are major ones.
Uneven ripening:
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Presence of green berries in a ripe bunch of coloured grapes is called uneven ripening. It is a varietal character and a problem in Bangalore Blue, Bangalore Purple, Beauty Seedless and Gulabi grapes. Within a variety this problem varies from bunch-to-bunch. Generally inadequate leaf area, and non-availability of reserves to a developing bunch is the reason. Cultural practices like cluster thinning, girdling and use of growth regulators can reduce uneven ripening. Application of Ethephon (25Oppm) at colour break stage is recommended to reduce the problem.
Postharvest berry drop:
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This is due to weak pedicel attachment to the berries. This is common in Anab-e-Shahi, Cheema Sahebi and Beauty Seedless. Spraying of NAA (50ppm), a week prior to harvesting can minimize the post-harvest berry drop.
Flower—bud and flower drop:
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When panicles are fully expanded, the flower-buds drop before the fruit set. This is common in north India but not in the south. The reasons for this disorder are not known. Stem girdling about 10 days prior to full bloom can reduce the problem.
Pink berry formation:
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It is a common disorder in Thompson Seedless and its clone Tas-A-Ganesh in Maharashtra. Pink blush develops on a few ripe berries close to harvesting. The pink colour turns to dull red colour and the berries become soft and watery. They do not stand for long after harvesting. Although the definite cause of the disorder is not known, it is recommended to spray a mixture of O.2% ascorbic acid and 0.25% sodium diethyl dithiocarbamate at fortnightly intervals commencing berry softening.
