Onion Eleventh to twelfth week practices

Damping-off:

The disease is more prevalent during kharif season and causes about 60-75% damage. High soil, moisture and moderate temperature along with high humidity especially in the rainy season leads to the development of the disease. Two types of symptoms are observed-

Pre-emergence damping-off: The pre-emergence damping off results in seed and seedling rot before these emerge out of the soil.

Post-emergence damping-off: The pathogen attacks the collar region of seedlings on the surface of soil. The collar portion rots and ultimately the seedlings collapse and die. 

Control: 

Healthy seed should be selected for sowing. The seed should be treated with Thiram @ 2g/kg of seed before sowing. Continuous raising of nurseries in the same plot should be avoided. The topsoil of the nursery should be treated with Thiram @ 5g/m² area of the soil and nursery should be drenched with the same chemical @ 2g/litre of water at fortnightly intervals. Soil solarization by spreading 250 gauge polythene sheets over the bed for 30 days before sowing and application of bio-control agent Trichoderma viride in soil @ 1.2kg/ha is also found effective to control damping-off to considerable extent.

Basal Rot:

The disease incidence is more in the area where the onion crop is grown continuously. A moderate temperature of 22-28°C favours disease development. Initially yellowing of leaves and stunted growth of the plant is observed and later on, the leaves dry from tip downwards. In the early stage of infection, the roots of the plants become pink in colour and rotting takes place later. In the advanced stage, the bulb starts decaying from lower ends and ultimately the whole plant dies. 

Control: 

Since the pathogen is soil borne, it is difficult to control disease. Mixed cropping and crop rotation reduce the incidence of disease. Soil solarization by spreading a polythene sheet of 250 gauge in the summer season for 30 days reduces the infectious propagules, which in turn reduces the disease. Seed treatment with Thiram (2 g/kg of seed) and soil application of Carbendazim, Thiophanate Methyl (Topsin-M) or Benomyl @ 0.1% is effective in controlling the disease. Seedling dip in Carbendazim (0.1%) or with antagonist viz. Pseudomonas cepacis, and Trichoderma viride significantly reduces the basal rot in onion crops.