Fungal Diseaseप्याज का बैंगनी धब्बा रोग (परपल ब्लॉच)Parts: Leaves, Stem
Purple Blotch of Onion (Alternaria porri)
Affects: Onion, Garlic
Primary Chemical Cure
Azoxystrobin 11% + Tebuconazole 18.3% SC (Custodia) or Nativo WG
250-300 ml Custodia or 100 gm Nativo per acre.
Economic Threshold (ETL)
First emergence of purple centers on older foliage.
Initiate spray only when crossed
Bio & Organic Option
Preventive spray of Pseudomonas fluorescens @ 5 gm/liter with organic sticker.
Key Visual Diagnostic Symptoms
Inspect Leaves and Stem in the field for these definitive physical manifestations:
- Small, water-soaked lesions that rapidly enlarge into oval, purplish-brown sunken patches.
- Surrounded by a characteristic broad yellow chlorotic border.
- Infected leaf tips snap over and die, stunting bulb development.
Weather & Climate Factors Fueling Outbreaks
Warm, humid weather (25°C to 30°C) with persistent cloudiness and free moisture on leaf surface.
Track real-time rain and humidity on our Aaj Ka Mausam Radar to preempt epidemics.
Preventive Agronomic & Cultural Controls
- Ensure proper bed drainage to avoid standing water around bulb root crowns.
- Always add an agricultural spreading agent (silicone adjuvant) to pierce the waxy onion cuticle.
Recommended Active Molecule
View technical dilution rates, rainfastness intervals, and genuine brands:
Azoxystrobin 11% + Tebuconazole 18.3% SC
Strobilurin + Triazole • 250 – 300 ml per acre
Calculate Chemical Spray Tank Mix
Calculate exact chemical dilution for your knapsack pump or field acreage before spraying.
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Frequently asked questions
The recommended chemical control is Azoxystrobin 11% + Tebuconazole 18.3% SC (Custodia) or Nativo WG, applied at 250-300 ml Custodia or 100 gm Nativo per acre.. Ensure complete foliage coverage, spraying during early morning or evening hours.
First emergence of purple centers on older foliage.. Chemical sprays should only be initiated when the pest population or disease incidence crosses this threshold to avoid unnecessary spray costs and pesticide resistance.
Yes. Preventive spray of Pseudomonas fluorescens @ 5 gm/liter with organic sticker.. Combining biological controls with cultural practices like crop rotation and removing infected plant debris offers sustainable control without chemical residues.
Purple Blotch of Onion (Alternaria porri) predominantly infects Onion, Garlic, attacking the Leaves, Stem.