DOWNY MILDEW OF GRAPEVINE
Causal Organism:
- Plasmopara viticola
- Sub-division: Mastigomycotina
Symptoms:
- Irregular, yellowish, translucent spots on the upper leaf surface.
- Corresponding dirty white, powdery fungal growth on the lower leaf surface.
- Infected leaves turn yellow, then brown, and eventually dry due to necrosis.
- Whitish fungal growth covers infected leaves, shoots, and tendrils.
- White fungal growth on berries that later becomes leathery and shriveled.
- Infected berries harden, turn bluish-green, then brown, and exhibit soft rot without skin cracking.
Disease Cycle:
- Primary Infection:Via sporangia or zoospores dispersed by wind and rain.
- Secondary Infection:Through oospores in infected leaves, shoots, and berries. Dormant mycelium in infected twigs also serves as a source.
Favourable Conditions:
- Temperature: 20-22°C
- Relative Humidity: 80-100%
Management:
- Collect and burn fallen leaves and twigs.
- Maintain orchard sanitation.
- Train vines high above ground to promote air circulation.
- Spray with 1% Bordeaux mixture or Copper oxychloride.
POWDERY MILDEW OF GRAPEVINE
Causal Organism:
- Uncinula necator (Imperfect Stage: Oidium tuckeri)
- Sub-division: Ascomycotina
Symptoms:
- Small whitish patches on both surfaces of young leaves.
- Patches enlarge, covering the leaf with a whitish powdery coating.
- In advanced stages, affected leaves become greyish-white, dwarfed, twisted, and malformed.
- Floral infection leads to flower shedding, discoloration, and poor fruit set.
- Powdery growth appears on older berries, leading to cracking of the berry skin.
Disease Cycle:
- Primary Infection: Through dormant mycelium and conidia in infected shoots and buds.
- Secondary Infection: Air-borne conidia spread the disease.
Favourable Conditions:
- Weather: Cool and dry.
- Temperature: 27-31°C
- Relative Humidity: Up to 91% (favorable during November and December).
Management:
- Practice clean cultivation by removing and destroying diseased parts.
- Spray with wettable sulphur @ 0.3% or use Karathane or Calixin @ 0.1%.
ANTHRACNOSE (BIRD’S EYE DISEASE) OF GRAPEVINE
Causal Organism:
- Elsinoe ampelina (Imperfect Stage: Gloeosporium ampelophagum)
- Sub-division: Ascomycotina
Symptoms:
- Circular, greyish-black spots with yellow halos on leaves.
- Center of spots becomes grey, sunken, and may fall off, leading to a ‘shot hole’ symptom.
- Sunken spots with ashy grey centers and dark margins on fruits, known as ‘Bird’s Eye’ symptom.
- Pinkish spore masses develop in the center of spots during warm, wet weather.
- Mummification and shedding of infected berries.
Disease Cycle:
- Primary Infection: Pathogen survives as dormant mycelium in stem cankers.
- Secondary Infection: Spread by conidia through air or water.
Favourable Conditions:
- Weather: Warm and wet conditions.
- Soil: Low-lying and poorly drained soils enhance disease severity.
Management:
- Remove and destroy infected twigs.
- Use disease-free cuttings for planting.
- Spray Bordeaux mixture (1%) four times a month from pruning until before fruit maturity.
- Spray with Carbendazim + Mancozeb @ 0.2%.
