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%.