Purple Blotch:
It is an important disease prevalent in all the onion growing areas. Hot and humid climate with temperature ranging from 21-30°C and relative humidity (80-90%) favour the development of the disease. It is more common in kharif season. The symptoms occur on leaves and flower stalks as small, sunken, whitish flecks with purple coloured centres. The lesions may girdle leaves/stalks and cause their drooping. The infected plants fail to develop bulbs .The intensity of disease varies from season to season.
White rot:
The initial symptom of the disease is yellowing and dieback of leaf tips. Scales, stem plates and roots get destroyed. The bulbs become soft and water soaked. White fluffy or cottony growths of mycelium with abundant black sclerotia resembling mustard grain are seen on the infected bulbs.
Control:
Repeated cultivation of onions on the same piece of land should be avoided. Crop rotation with cereal crops is recommended.
Seed treatment with Thiram (4 g/kg of seed) and drenching of soil with Mancozeb (0.25%) are effective in controlling the disease. Application of bio-control agents like Trichoderma viride to the soil reduces the disease inoculum.
Neck rot:
The infection usually takes place in the field and symptoms become evident in storage. It is more severe when moist conditions prevail just before and during harvest and while onions are cured in the field. Excessive nitrogen and untimely irrigation increases the incidence of this disease, which is more severe in mild than in pungent onions. The fungus causes softening of the scales which appear water soaked. Under moist conditions, a grayish fungal mat develops on the surface of the scales.
Control:
For effective control of die disease, leave it to dry in the field for two days. These bulbs should be further dried in shade for 10-15 days before storage. Care should be taken to avoid injury to the bulbs during post-harvest handling. The crops should be sprayed with Carbendazim (0.2%) 10-15 days before harvesting
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