Purple blotch is a soil-borne disease. Symptoms of this disease are small, sunken, white spots on onion leaves and stalks with purple centres. Its lesions surround the leaves/stalks and can cause them to drop. Infected plants fail to develop bulbs.
Prevention Measures:
Use healthy seeds for sowing.
Adopt crop rotation of 2-3 years and make a proper drainage system.
Use recommended doses of fertilizers containing nitrogen and phosphorous.
Before sowing, treat the seeds in hot water for 20 minutes at 50 °C and select resistant varieties.
Soil Treatment: To protect against this disease, spread Trichoderma viridi 500 gm in soil with 4 to 5 tonnes of well-decomposed cow dung per acre evenly before sowing. Re-use Trichoderma Viridi 500g/acre after 30 days.
Chemical Control:
Seed Treatment: Before sowing, treat the seeds with Carmanova 2.5 gm/kg seed solution.
Preventive measures at the onset of disease symptoms: Spray Hexaconazole 5% SC (Novacone), @ 400 ml + Silicomax (sticker) @ 50 ml per acre in 200 litres of water or Kitazin 48 when the initial symptoms of the disease appear. Spray % EC @ 200 ml + Silicomax (sticker), @ 50 ml per acre in 200 liters of water or spray Pseudomonas fluorescens (Monas curb @ 250 g @ 250 g in 200 liters of water) for biological control.
