Early Blight of Potato

Early blight (EB) is a disease of potato caused by the fungus Alternaria solani. It is found wherever potatoes are grown. The disease primarily affects leaves and stems, but under favorable weather conditions, and if left uncontrolled, can result in considerable defoliation and enhance the chance for tuber infection. Premature defoliation may lead to considerable reduction in yield. The disease can also be severe on …

Early blight (EB) is a disease of potato caused by the fungus Alternaria solani. It is found wherever potatoes are grown. The disease primarily affects leaves and stems, but under favorable weather conditions, and if left uncontrolled, can result in considerable defoliation and enhance the chance for tuber infection. Premature defoliation may lead to considerable reduction in yield. The disease can also be severe on tomatoes, and can occur on other solanaceous crops and weeds.

Symptoms :The initial symptoms appear in the form of small, isolated scattered pale brown spots on leaves with deep greenish-blue fungal growth. The lower leaves are attacked first and then the disease progresses upwards. In the necrotic tissue, concentric rings develop, which give a target board effect. There is usually a narrow chlorotic zone around the spots fading into normal green. In case of severe infection, the leaves are shriveled and fall down. The stem lesions often girdle it and cause Collar – rot in young seedling plants leading to collapse of branches or entire above ground portion. On tubers the affected region is darker than the healthy area and the lesion soon shrinks slightly as dry, corky rot develops.

Casual Organism : Alternaria solani

Disease Cycle: Mycelium and conidia can survive in plant debris and on seed tubers. The conidia germinate in moist weather and cause primary infection directly or through stomata, first on lower and then on upper leaves. The secondary infection takes place through conidia carried by wind, water or insects.

Epidemiology : The optimum temperature for conidial germination is 28-30°C. If season starts with abundant moisture and frequent rains, disease becomes serious, followed by warm and dry weather, which is unfavourable for the host but helps rapid disease development. Weaker plants are more susceptible.

Control :

1. Crop rotation and field sanitation is a rational measure to avoid primary infection from spores that have survived from previous crop.
2. Fungicidal sprays starting from 30 days after sowing at an interval of 10-21 days (depending upon the intensity of disease). For this purpose, Bordeaux Mixture (4:4:50), Dithane M-45 (0.6%), Daconil (0.3%), Acrobat MZ, Ridomil Gold MZ, Banko (0.2 – 0.25%) can be used.
3. Proper fertilization of the crop to maintain the plant vigour.