Thrips are the most serious pests of onion all over the country. Sometimes 50-60% losses in bulb crop are observed due to thrips attack. Thrips are found in the axil of green leaves where these suck the juice of early-emerging leaves. Small white silvery patches are seen all over the leaves. The infested plants show stunted growth with twisted leaves. If the infestation comes in the early stage of growth, bulb formation stops completely.
In pre-emergence damping off, seedlings are killed before they reach the soil surface. Post emergence is characterised by the toppling of seedlings anytime after they emerge from the soil. It is more common during Kharif season with temperature and humidity are high
It is common in Northern and Eastern India. Its severity varies from 5 to 50 % and is more severe in rabi than Kharif crop during March and April. Small yellow to pale orange spots or streaks develop on the middle of leaves stalk on one side. The spots frequently coalesce into extended patches to cover the entire foliage. In seed crop, inflorescence stalk is severely damaged.
It is common during Kharif season. Hot and humid climate with a temperature of 25-30oC and relative humidity of 80-90 % favour development and spread of the diseases. The disease appears as small whitish sunken lesions which enlarge and coalesce covering the entire leaf. Concentric zones may develop within the lesions
1.Rice root-knot nematode
Usually, young seedlings are infected and thus may result in complete destruction of the crop. Infection by nematode causes abnormal swelling of roots known as root knot or galls, yellowing, wilting and stunting of plants.
Validated Integrated Pest Management Interventions for Onion Crop
- Raised nursery beds up to 10 cm above ground level with good drainage and rice bran ash.
- Mix entire nursery bed with effective strains of Trichoderma spp.@ 50 g / 3 sq. m with FYM / vermicompost
- Need based spray of urea @ 0.2% to reduce yellowing caused due to unprecedented rains during January-February Main Crop
- Planting outer row maize as barrier crop against onion thrips.
- Seedling dip in Pseudomonas inflorescence before transplanting @ 5 ml/litre.
- Give adequate irrigation during crop season as thrips pupae get rotten in soil with continuous retention of moisture.
- Irrigating fields through sprinkler wash off the thrips.
- Install blue coloured sticky traps @ 20 / acre for thrips management.
- Need based application of sulphur 80 WP @ 0.2% or for sulphur deficiency.
- Spray the crop with dimethoate 30 EC @ 660 ml or fipronil 80 WG @ 75 g or oxy-demeton methyl 25 EC @ 1.2 litre / ha in 500 lit water for protection against thrips. Thrips control is critical during bulb initiation stage i.e. a seventh week or 50 days after transplanting (DAT).These are effective even at higher temperature against thrips when population crosses ETL of 30 thrips/plant. Addition of sticker (0.1%) is essential for retention of spray fluid on leaves.
- Need based application of neem cake @ 250 kg/ha for nematode management.
- Spray zineb 75 WP @ 1.5-2 kg / ha in 750-1000 lit water against downy mildew and blight.
- Need- based spray with difenconazole @ 0.1 % or tebucunazole 25.9 % m / m EC @ 625-750 ml / ha in 500 lit water or metiram 55 % + pyraclostrobin 5 WG @ 1500-1750 g / ha in 750 lit water against purple blotch.
Conservation of natural enemies
The commonly seen natural enemies of pests in onion cropping system should be protected from unwanted and excessive sprays of chemical pesticides.
- National Research Centre for Integrated Pest Management.