KAU Agri Infotech Portal

Onion (Allium cepa L.)

Purple blotch (Alternaria porri)

Symptoms

The symptoms occur on leaves and flower stalks as water-soaked small, sunken, whitish flecks with a purple coloured centres and zonations.
These blotches have prominent yellow halo that extends upward and downward for some distance.
Circular to oblong concentric black velvety rings appear in the chlorotic area.
The lesions develop towards the base of the leaf.
The lesions may girdle leaves or stalk and cause their drooping.
The infected plants fail to develop bulbs and if bulbs develop, they decay.

Management

Use of healthy and disease free seeds for planting.
Crop rotation of 2-3 years with non-related crops.
The field should be well drained.
Follow proper drainage at regular intervals
Use the recommended doses of N and P fertilizers.
Hot water soaking of garlic seed (50 °C for 20 minutes).
Use resistant varieties.
Seed treatment with Trichoderma viride or Pseudomonas fluorescens (20 g/litre of water/ kg of seeds).

Chemical Control

Sl.No	Generic Name	Trade Name	Color code	Dosage/litre	Knapsack Sprayer (Capacity 10L)	Recommendation		Remarks
Sl.No	Generic Name	Trade Name	Color code	Dosage/litre	Knapsack Sprayer (Capacity 10L)	Dosage/acre (200 L)	Dosage/hectare (500 L)	Remarks
1	Carbendazim 50 WP	Bavistin, Benfil, Bengard, Benlate, Benmain, Bensaan, Carben, Carziim50, Dhanustin, Dhanustin 50 WP, Fungiguard, Gancarzin50, Glizim, Mintho, Tagstin, Tiara, Zoom	Green	2 g/ litre of water/kg of seed	-	-	-	Seed treatment
2	Mancozeb 75 WP	Devidayal M-45, Dhanuka M 45, Dhanuka M-45, Dithane, Dithane M-45, Hilthane, Hindustan M 45, Indofil M 45, Izeb M-45 Manzate, Luzen-45, Macoban, Macoban M-45, Mancosaan, Mancosaan M-45, Maneb Manzane, M-Guard, Savour M 45, Tata M-45 Eurofil-NT, Uthane M-45, Veera, Zinthane	Green	4 g/ litre of water/kg of seed	-	-	-	Seed treatment
3	Thiram 75 WS	Hexathir, Tagithram, Thiram 75 DS, Thiride, Vegfru Thiram	Blue	4 g/kg of seed	-	-	-	Seed treatment
4	Copper hydroxide 77 WP	HiDice, Kocide 101	Blue	1 g/ litre of water	10 g	200 g	500 g	-
5	Copper oxychloride 50 WP	Bensaan, Blitox, Blue copper, Bluetrox, Copter, Cupramar, Cuprina, Dhanucop, Fytolan, Fytox, Fytran, Fytolan, Hilcopper, Killex copper, Maincop Dhanucop, Star cop, Tagcop, Trucop	Blue	2 g/ litre of water	20 g	400 g	1000 g	-
6	Mancozeb 75 WP	Devidayal M-45, Dhanuka M 45, Dhanuka M-45, Dithane, Dithane M-45, Hilthane, Hindustan M 45, Indofil M 45, Izeb M-45 Manzate, Luzen-45, Macoban, Macoban M-45, Mancosaan, Mancosaan M-45, Maneb Manzane, M-Guard, Savour M 45, Tata M-45 Eurofil-NT, Uthane M-45, Veera, Zinthane	Green	3 g/ litre of water	30 g	600 g	1500 g	-
7	Carbendazim 50 WP	Bavistin, Benfil, Bengard, Benlate, Benmain, Bensaan, Carben, Carziim50, Dhanustin, Dhanustin 50 WP, Fungiguard, Gancarzin50, Glizim, Mintho, Tagstin, Tiara, Zoom	Green	1 g/ litre of water	10 g	200 g	500 g	-