Major Grapevine diseases are:-
1.Downy mildew: Plasmopara viticola
- Irregular, yellowish, translucent spots on the upper surface of the leaves.
- Correspondingly on the lower surface, white, powdery growth on leaves.
- Affected leaves become, yellow, brown and get dried.
- Premature defoliation.
- Dwarfing of tender shoots.
- Brown, sunken lesions on the stem.
- White growth of fungus on berries which subsequently becomes leathery and
- Later infection of berries results in soft rot symptoms.
- No cracking of the skin of the berries.
- Spread: Through sporangia by wind, rain etc.
- Survival: As oospores present in the infected leaves, shoots and berries. Also as dormant mycelium in infected twigs.
- Optimum temperature: 20-22°C
- Relative humidity: 80-100 percent
- Spray Bordeaux mixture 1 % or Metalaxyl + Mancozeb 0.4 %.
2.Powdery mildew: Uncinula necator
- Powdery growth mostly on the upper surface of the leaves.
- Malformation and discolouration of affected leaves.
- Discolouration of the stem to dark brown.
- Floral infection results in shedding of flowers and poor fruit set.
- Early berry infection results in shedding of affected berries.
- Powdery growth is visible on older berries and the infection results in the
- Cracking of skin of the berries.
- It spread through air-borne conidia
- Through dormant mycelium and conidia present in the infected shoots and buds.
- Sultry warm conditions with the dull cloudy weather, highly favourable.
- Spray Inorganic sulphur 0.25 % or Chinomethionate 0.1 % or Dinocap 0.05 %.
3.Bird’s Eye Spot/Anthracnos: Gloeosporium ampelophagum Elsinoe amphelina
- The disease appears first as dark red spots on the berry.
- Later, these spots are circular, sunken, ashy-gray and in late stages these spots are surrounded by a dark margin which gives it the “bird’s-eye rot” appearance.
- The spots vary in size from 1/4 inch in diameter to about half the fruit.
- The fungus also attacks shoots, tendrils, petioles, leaf veins, and fruit stems.
- Numerous spots sometimes occur on the young shoots.
- These spots may unite and girdle the stem, causing death of the tips.
- Spots on petioles and leaves cause them to curl or become distorted
- Seed-borne-infected vine, cuttings and air-borne conidia
- As dormant mycelium in the infected stem-cankers
- Warm wet weather
- Low lying and badly drained soils.
- Removal of infected twigs
- Copper oxychloride 0.2% or Mancozeb 0.25%
- TamilNadu Agritech Portal