The following points highlight the seven major diseases of grapes fruit. The disease are: 1. Anthracnose 2. Cercospora Leaf Spot 3. Downy Mildew 4. Powdery Mildew 5. Foot Rot 6. Rotting of Berries 7. Water Berry.
Disease # 1. Anthracnose or Die Back:
The disease is caused by the fungus Elsinoe ampelina Shear. Small light brown spots appear on young leaves which later enlarge, turn dark brown and give shot-hole appearance. In severe attack, early defoliation occurs. Dark brown sunken spots with raised margins develop on new shoots/canes leading to their death from tip backwards.
Similar spots appear on laterals of clusters. Under favourable conditions dark brown depressed spots appear on berries also. On the berries, the disease is referred to as ‘bird’s eye spot’ because of the grey centre surrounded by a reddish-brown zone.
Control:
(i) Prune the shoots and canes during January-February and give one dormant spray of Bordeaux mixture (2:2:250) after pruning using 125 litres of water per acre.
(ii) Spray with Bordeaux mixture (2:2:250) in the last week of March using 250 litres of water per acre.
(iii) Spray Bavistin 50 WP @ 500 g per acre in last week of April using 500 litres of water.
(iv) Spray Bordeaux mixture (2:2:250) in the last week of May in 500 litres of water per acre.
(v) Spray Score 25 EC @ 500 ml in mid-July and Bavistin 50 WP @ 500g per acre in end July using 500 litres of water.
(vi) Spray Score 25 EC @ 500 ml in mid-August and Bordeaux mixture (2:2:250) in end August in 500 litres of water per acre.
(vii) Spray Score 25 EC @ 500 ml in mid-September and Bordeaux mixture in end September using 500 litres of water.
Disease # 2. Cercospora Leaf Spot:
The disease is caused by Cercospora spp. The disease appears in March-April but becomes serious from August onwards with maximum attack during September-October. Necrotic small area on leaves with straw coloured centre and reddish brown margins appear. Severe attack results into drying of leaves and early defoliation.
Control:
(i) Proper fertilization of the vines results into reduced attack of leaf spot,
(ii) Spray the fungicides as recommended for anthracnose.
Disease # 3. Downy Mildew:
Downy mildew is caused by fungus Plasmopara viticola (Berk and Curt). Light yellow oily spots appear on upper surface of leaves which on the lower surface are covered with white downy growth of the pathogens. Later, the spots become brown and brittle.
Leaves with many active spots drop pre-maturely. The diseases start appearing in nursery and on grown up vines in March-April. After rainy season i.e., August-September, it assume serious proportions and continue to appear in humid weather. It affects tendrils and fresh growth of the shoots also.
Control:
(i) All the pruned canes should be destroyed as the buds may contain dormant mycelium.
(ii) Old fallen leaves should be collected from the orchard soil and destroyed.
(iii) Other control measures are the same as for anthracnose. Give one additional spray of Bordeaux mixture (2:2:250) in mid-September using 500 litres of water per acre.
Disease # 4. Powdery Mildew:
The disease is caused by an Ascomycite Uncinula necator (Schw). The fungus spreads over the new shoots, leaves and canes in the spring and later infects the berries. It is one of the most important and widely distributed diseases of grapes.
The disease may be found on new growth and is more conspicuous on the upper surface of the leaves. The entire leaf surface may be covered by indistinct white patches which later have a powdery appearance. Usually, they enlarge so that the entire upper surface of the leaf has a dusty coating.
The severely attacked leaves curl upwards during warm dry weather. They, however, usually retain their normal green colour but may show some discolouration towards the end of the season Spots on the canes are of the same general appearance as on the leaves.
The young berries may have spotting as on the leaves and show powdery growth of the fungus on its entire surface. Damage to the fruit may result in rusty spotting and misshapen berries. Sometimes the fruit splits as a result of the retarded growth of the infected area.
Control:
(i) Spray the vines with 0.25% wettable sulphur (1.25 kg in 500 litre of water).
(ii) Spray Bayleton @ 200g or Topas 10 EC @ 200 ml in 500 litres of water in mid-March, last week of April and first week of May.
Disease # 5. Foot Rot or Collar Rot:
This disease is especially present in grape cuttings and young vines and is caused by Rhizoctonia sp. In the case of young vines the roots and the collar region turn brownish with the shredding of bark and internal brown discoloration. Ultimately the vines wilt and die. Leaves turn yellow and ultimately the vines wilt and die.
Control:
(i) The cuttings for planting should be dipped into 0.2% Ziram suspension (2 g per litre of water).
(ii) The soil in the pit should be drenched with 0.4 percent Captan (400 g in 100 litres of water) thoroughly before planting the cuttings.
Disease # 6. Rotting of Berries:
Various kinds of air-borne fungi like Penicillium, Aspergillus, Rhizopus, Botrytis etc. attack the maturing or matured fruit and cause blue mould rot, black mould rot, Rhizopus rot and Botrytis rot, respectively. Grapes berries, are attacked when still on the vine.
The wasps aid in injuring the berries and releasing the juice which serves as substrate for the growth of fungi. In Perlette, which has compact bunches, the growth pressure ruptures some berries and released juice flows into other berries where fungi grow and causes various types of rotting.
Control:
(i) In case of compact bunched varieties such as Perlette, practice the thinning of bunches as recommended under thinning.
(ii) Use insecticides or repellents to guard against wasps and other insects causing injuries to berries.
(iii) During June, spray grapevine with 0.2% Ziram (1 kg per 500 litres of water) at 7 day interval. Stop spraying a week before harvesting the bunches.
Disease # 7. Water Berry:
This disorder is caused due to water stress or excessive nitrogenous fertilizer or over-bearing. The drying of berries is at the tips or is scattered all over the bunches during May and June. Berries look like small cellophane bags, half filled with sap and remain hanging on the bunches.
Control:
(i) Apply frequent irrigation during the summer (May and June).
(ii) Practice a proper thinning of the over bearing vines.