Downy Mildew

Causal Organism:

• Pseudoperonospora cubensis
• Sub-division: Mastigomycotina

Etiology:

• The pathogen is an obligate parasite that survives on collateral hosts or in plant debris.
• Produces sporangia that are dispersed by wind or splashing rainwater.

Symptoms:

• On Leaves:
  • Yellow, angular spots on the upper surface.
  • Purplish downy growth on the lower surface under moist conditions.
  • Leaves turn yellow, dry, and fall off prematurely.
  • Stunted plant growth and poor fruit development.

Disease Cycle:

• Primary Infection: Fungus survives on collateral hosts or plant debris.
• Secondary Infection: Spread by wind-borne sporangia or splashing rainwater.

Favorable Conditions:

• Cool (15-25°C) and moist weather.
• High relative humidity (>85%).

Management:

• Cultural Practices:
  • Remove and destroy infected plant debris.
  • Avoid overhead irrigation to reduce leaf wetness.
  • Practice crop rotation with non-cucurbit crops.
• Chemical Control:
  • Metalaxyl + Mancozeb @ 0.2% spray at the first sign of disease.
  • Repeat applications at 7-10 day intervals during favorable conditions.

Powdery Mildew

Causal Organisms:

• Erysiphe cichoracearum
• Sphaerotheca fuligena
• Sub-division: Ascomycotina

Etiology:

• Obligate parasite producing conidia that are dispersed by wind.
• Can survive in crop debris or as cleistothecia (sexual spores).

Symptoms:

• On Foliage, Stems, and Growing Parts:
  • Whitish or dirty grey powdery growth.
  • Affected areas turn brown and dry up.
  • Severe infection causes premature leaf fall and plant death.

Disease Cycle:

• Primary Infection: Initiated by ascospores from cleistothecia.
• Secondary Infection: Spread by wind-borne conidia.

Favorable Conditions:

• Cool dry weather for conidial germination (20-27°C).
• High Relative Humidity (>50%) favors disease development.

Management:

• Cultural Practices: Use resistant varieties when available. Ensure proper plant spacing for good air circulation.
• Chemical Control:
  • Spray Calixin @ 0.1% or Karathane @ 0.2%.
  • Sulfur dusting or Neem oil sprays are also effective.

Vascular Wilt

Causal Organism:

• Erwinia tracheiphila
• Type: Bacterial Disease

Etiology:

• Bacterium is transmitted by the Striped Cucumber Beetle (Acalymma vittatum) and Spotted Cucumber Beetle (Diabrotica undecimpunctata).
• Bacteria enter through feeding wounds on the plant.

Symptoms:

• On Leaves and Whole Plant:
  • Initial wilting of a single leaf that spreads throughout the plant.
  • Leaves become dull green and wilt without yellowing.
  • Entire plant collapses and dies.
  • Creamy white bacterial ooze seen when infected stem is cut and squeezed.

Disease Cycle:

• Primary Infection: Bacteria survive in the gut of striped cucumber beetles.
• Secondary Infection: Spread occurs as beetles move from plant to plant while feeding.

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Favorable Conditions:

• Monocropping of cucurbits increases beetle populations.
• High beetle populations during warm growing seasons.

Management:

• Cultural Practices:
  • Plant resistant cultivars if available.
  • Remove and destroy infected plants to prevent spread.
• Insect Control:
  • Carbaryl (Sevin), Malathion, or Rotenone sprays to control cucumber beetles.
  • Row covers can be used to protect young plants from beetle feeding.
• Preventive Measures:
  • Start insect control early, as soon as seedlings emerge.
  • Practice crop rotation to break the life cycle of the beetles.