Symptoms and Management Alternaria blight/Leaf blotch/Purple blotch of Onion and Garlic
Causal organism: Alternaria Porri .
Origin The disease was first reported by Ajrekar from Bombay in 1921.
Symptoms of Purple Blotch of Onion and Garlic
1. Symptoms first appear on leaves or seed stalks as small water-soaked lesions that quickly develop white centers. 2. Under favourable condition, these lesions enlarge, coalesce, become zonate and brown to purple that extend upward and downward.
3. In moist weather, the surface of the lesion, may be covered with black fruiting bodies of fungus. 4. The older leaves are more susceptible than younger leaves and younger leaves relatively more susceptible when they emerge close to bulb maturity. 5. Similar lesion may form on seed stalk, as a results seed either do not develop or are shriveled. The infected plants fail to develop bulbs.
6. Severely infected foliage of onion and garlic may exhibit dieback. 7. The bulb can also be affected at harvest when the fungus enters through the neck or injurious, causing storage rot.
Favourable conditions of Purple blotch of Onion and Garlic
Hot and humid climate with temperature ranging from 2130°C and high relative humidity (80-90%) favor the development of the disease.
Control Measures/Management of Purple blotch of Onion and Garlic
♦ Healthy seed should be used.
♦ Seed should be treated with Thiram @ 4 g/kg of seed.
♦ Crop rotation of 23 years with non related crops should be followed.
♦ Mancozeb @ 0.25% or chlorothalonil @ 0.2% or rovral @ 0.25% should be sprayed at fortnightly interval commencing from one month after transplanting.The sticker triton/sandovit should be mixed in spray solution.