Onion (Allium cepa L.; family Amaryllidaceae) is one of India's most important commercial vegetables, grown in the western, northern and southern parts of the country. Maharashtra, Gujarat, Uttar Pradesh, Odisha, Karnataka, Tamil Nadu, Madhya Pradesh, Andhra Pradesh and Bihar are the major onion-growing states. India ranks second in the world for onion production after China; within India, Gujarat stands second after Maharashtra. The all-India average productivity is about 12,580 kg/ha, while Gujarat records the highest at around 22,120 kg/ha.
Onion is a cool-season crop that still tolerates a wide range of conditions. The ideal temperature is 12.8-21°C for vegetative growth and 15.5-25°C for bulb development; very low temperatures early on favour bolting, while a sudden rise in rabi causes early maturity and small bulbs. It grows best on Goradu and medium black soils with good drainage and organic matter, at a pH of 5.8-6.5.
Early identification matters: thrips alone can wreck both yield and quality by opening the way for blast and viral infection, while damping-off can cause 60-75% nursery loss and bulb rots make the produce unsellable. This guide brings together the full integrated pest management (IPM) approach — pest and disease identification, favourable conditions, cultural, biological and chemical practices, crop-stage timing, nutrition and digital monitoring.
Major insect and mite pests of onion
1. Onion thrips (Thrips tabaci)
Onion thrips is the single most damaging pest of onion across India. Adults are about 1.5 mm long with slender yellow-brown bodies and two pairs of fringed wings; the pale, wingless larvae feed alongside them deep in the centre of the onion neck.
Symptoms of damage: Both adults and larvae feed within the leaf using a punch-and-suck action, puncturing the epidermis and drawing out sap. Removal of chlorophyll leaves silvery-white patches and streaks on the leaves. Under heavy feeding, leaves take on a silvery cast and wither, and tiny black "tar" spots of excrement appear. Thrips also transmit Iris yellow spot virus, and their feeding wounds open the door to blast and bulb-quality loss.
Favourable conditions: Hot, dry weather favours rapid thrips build-up. High nitrogen and frequent irrigation make the crop more succulent and more attractive to thrips.
Cultural control:
- Use resistant/tolerant varieties (TNAU hybrids CO2, CO3, CO4) and practise field sanitation.
- Avoid planting successively after garlic or other preferred hosts such as cabbage, cotton, tomato, cucumber and melons, and plant new crops upwind of older ones.
- Use reflective silver or aluminium-painted black mulch to repel thrips in seed crops.
- Prefer sprinkler irrigation, which suppresses thrips far better than drip or surface irrigation.
- Plant two border rows of maize (or an inner row of wheat with an outer row of maize) around the plot as a barrier crop.
Mechanical control: Set up blue pan-water or sticky traps at 4-5 per acre, 15 cm above the canopy, to monitor and mass-trap thrips. Locally available tins painted blue and smeared with grease, Vaseline or castor oil work too.
Threshold monitoring made simple: Using Fyllo Smart Sticky Traps, growers can track thrips populations digitally and get alerts for the specific pest, with the spray chemical names, required quantity and schedule, when numbers cross the threshold — directly on their phone via the Fyllo App. This removes the need to count tiny thrips on sticky cards by hand every few days.
Biological control: Conserve the nymphal parasitoid Ceranisus menes and predators such as syrphid flies, minute pirate/anthocorid bugs (Orius spp.), predatory thrips (Aeolothrips fasciatum), damsel bugs, lacewings, coccinellids (Cheilomenes sexmaculata) and spiders.
Chemical control: Only when the pest population crosses the threshold and the pest-to-defender (P:D) ratio is unfavourable, spray Fluxametamide 25 EC @ 1 mL/L or Broflanilide 300 GL @ 0.36 mL/L; Fipronil 5 SC @ 1.5 mL/L is another registered option. Use high pressure and volume, direct the nozzle at the base of the leaves, and add a spreader/sticker (0.05-1.0%) so the spray holds on the erect leaves. In seed crops, control thrips well before the flowers open, and rotate chemical classes to prevent resistance.
2. Onion maggot (Delia antiqua)
The onion fly lays white, elongated eggs on the soil near the stem; the legless, creamy-white maggots (about 8 mm when full-grown) are the damaging stage.
Symptoms of damage: Maggots use hooked mouthparts to enter the base of the plant and feed on roots and the basal plate of the bulb. Damaged seedlings first wilt, then become flaccid and die, often forcing maggots to move to neighbouring plants. Second-generation feeding on developing bulbs causes distorted growth with rotting tissue; late-season feeding makes bulbs unmarketable.
Favourable conditions: Cool, moist soils and close spacing favour maggot survival; any wound on the bulb eases their entry.
Cultural control: Avoid close spacing, follow crop rotation with non-host crops, and maintain strict field sanitation.
Biological control: Conserve ground beetles, rove beetles and spiders by keeping grassy refuge strips at field margins.
3. Mites — bulb mite, eriophyid mite and red spider mite
Three mites attack onion. The bulb mite (Rhizoglyphus robini) is a shiny white mite that enters injured bulbs and rapidly turns them to rotten pulp — usually a secondary invader of already-damaged bulbs. The eriophyid mite (Aceria tulipae) feeds on young leaves and between bulb scales, causing stunting, twisting, curling and discolouration, and is linked to virus transmission. The red spider mite (Tetranychus cinnabarinus) feeds on leaf undersides, leaving stippled, bleached foliage with fine silk webbing; it thrives in hot, dry weather.
Cultural control: Flood irrigation reduces bulb-mite and eriophyid-mite levels in the soil; avoid planting onion after cole crops (especially cauliflower) or in continuous onion/garlic rotations; a thorough water spray washes red spider mites off the plants.
Biological control: Conserve predatory mites (Amblyseius spp., Phytoseiulus persimilis), anthocorid bugs (Orius spp.), green lacewings (Mallada basalis, Chrysoperla zastrowi sillemi), predatory coccinellids (Stethorus punctillum), staphylinid beetles (Oligota spp.) and spiders. Beauveria bassiana is a useful entomopathogen against mites.
Other pests at a glance
Besides the pests of national significance above, a few caterpillars are important in particular states. Because they are leaf- and pod-feeding moths, their adults and egg masses can be monitored and intercepted, but their larvae bore and feed concealed, so sticky traps do not control the larval stage.
| Pest | Key damage | Main control measure |
|---|---|---|
| Gram pod borer (Helicoverpa armigera) — Punjab | Larvae scrape and feed on leaves | Pheromone traps @ 4-5/acre; bird perches @ 20/acre; release Trichogramma pretiosum @ 40,000/acre weekly from flower initiation |
| Tobacco caterpillar (Spodoptera litura) | Larvae feed on foliage, heavy defoliation in severe cases | Hand-pick egg masses; pheromone and light traps; ecological engineering with cowpea/maize guard rows; EPNs (Steinernema feltiae) @ 20-120 crore IJ/acre |
| Cutworm (Agrotis ipsilon) — Assam | Larvae cut seedlings at the base at night | Field sanitation; deep summer ploughing; monitor with pheromone traps @ 4-5/acre |
Major diseases of onion
1. Damping-off (Pythium, Rhizoctonia, Fusarium, Sclerotium spp.)
A destructive nursery disease with two phases: pre-emergence rot kills seed and seedlings before they emerge, while post-emergence damping-off rots the collar region at the soil surface so seedlings collapse and die.
Favourable conditions: Most severe in the kharif/rainy season, causing about 60-75% damage; high soil moisture with moderate temperature and high humidity drive the disease.
Cultural control:
- Raise the nursery on raised beds (more than 15 cm high for drainage) and avoid excessive watering.
- Solarise nursery beds with transparent polythene for 30 days before sowing, and do not raise the nursery continuously in the same plot.
- Sow clean, healthy seed thinly on well-decomposed FYM.
- > Treat seed/seedlings with Trichoderma spp. and Pseudomonas fluorescens*.
2. Purple blotch (Alternaria porri)
The most common foliar disease of onion. Symptoms appear on leaves and flower stalks as small, sunken, whitish flecks with purple-coloured centres; the lesions enlarge, girdle the leaf or stalk and cause drooping, and badly infected plants fail to form bulbs.
Favourable conditions: Hot, humid weather of 21-30°C with 80-90% relative humidity.
Cultural control: Use healthy seed and resistant varieties (TNAU hybrid CO2); follow 2-3 year rotation with non-host crops; ensure good drainage; use recommended N and P doses; and give seed a hot-water soak (50°C for 20 minutes).
Chemical control: Spray difenoconazole 25% EC @ 40 ml in 200 l of water/acre, or kitazin (iprobenfos) 48% EC @ 80 ml in 80 l of water/acre, adjusting volume to crop stage and equipment.
3. Stemphylium leaf blight (Stemphylium vesicarium)
Infection starts on the radial leaves of transplanted seedlings at the 3-4 leaf stage. Small yellowish to orange flecks or streaks appear in the middle of the leaves and develop into elongated, spindle-shaped spots with a pinkish margin. On the seed crop, infection of the inflorescence stalk causes severe loss.
Favourable conditions: Warm, humid weather of 18-25°C with long periods (16 hours or more) of leaf wetness.
Cultural control: Collect and burn crop residues; follow long rotations with non-host crops; improve field drainage and reduce plant density; give seed a hot-water soak (50°C for 20 minutes).
Chemical control: Spray mancozeb 75% WP @ 600-800 g in 300 l of water/acre, or zineb 75% WP @ 600-800 g in 300-400 l of water/acre.
4. Colletotrichum blight / anthracnose / twister disease (Colletotrichum gloeosporioides)
Water-soaked, pale-yellow spots appear on the leaves and spread lengthwise to cover the whole blade; affected leaves shrivel, curl and droop, and the characteristic twisting and abnormal elongation of leaves gives the "twister" name.
Favourable conditions: Most severe in warm (25-30°C), moist soils high in organic matter; fungal growth slows sharply below 15°C.
Cultural control: Practise field sanitation by destroying infected plant debris, and grow resistant varieties.
5. Fusarium basal rot (Fusarium oxysporum f. sp. cepae)
Leaves yellow and the plant is stunted, drying from the tip downwards. Infected roots turn pink and rot; in advanced stages the bulb decays from the lower (basal) end until the whole plant dies.
Favourable conditions: Moist soil and temperatures around 27°C.
Cultural control:
- Follow 4-5 year rotation with non-host crops, and try mixed cropping with tobacco and sorghum to lower inoculum.
- Solarise soil with 25-gauge polythene for 30 days in summer.
- Ensure good drainage and deep summer ploughing.
- Avoid injury during cultural operations, and use resistant varieties.
6. Bulb rots in storage — white rot, pink root, black mould, green mould and bacterial rots
Several pathogens attack bulbs in the field and in storage. White rot (Sclerotium cepivorum) yellows leaf tips, then rots scales and roots with white cottony mycelium bearing black, mustard-sized sclerotia — worst in cool, dry soils. Pink root rot (Phoma terrestris) turns roots pink to maroon and shrinks bulb size (optimum 24-28°C). Black mould (Aspergillus niger) and green mould enter through the neck as foliage dies down, producing powdery black or green spores; they are worst above 30°C in the field or 24°C in storage with surface moisture. Bacterial soft rot and brown rot / slippery skin turn inner scales watery and foul-smelling so the rotted core slides out of the neck — favoured by warm, humid 20-30°C conditions.
Cultural control: Grow the crop with balanced nutrition, good tilth and drainage, and crop rotation; cure and dry bulbs quickly after harvest (two days in the field, then 10-15 days in shade); discard affected bulbs before storage; maintain aeration; avoid bruising; and store onions cool (ideally 1-15°C). For white and pink root rot, rotate with cereals and green-manure crops and solarise the soil; hot-water treatment of bulbs (49°C) helps against white rot.
7. Viral diseases — Iris yellow spot and onion yellow dwarf
Iris yellow spot virus (IYSV) shows as cream, elliptical or diamond-shaped spots on leaves and flower stalks (scapes), which can collapse at the spot; it is transmitted by onion thrips in a persistent manner, so disease severity rises with thrips numbers. Onion yellow dwarf virus shows yellow streaks at the base of the first true leaves, progressing to complete yellowing, crinkling and flattening of leaves and undersized bulbs; it is carried by infected seed bulbs and onion sets and spread by aphids.
Cultural control: Plant healthy, thrips-free and virus-free transplants; follow three-year or longer rotation between onion crops; remove and destroy diseased plants (roguing) and alternate hosts, culls and weeds; use sprinkler irrigation to suppress thrips; and set up blue sticky traps to monitor the vectors. Managing the thrips and aphid vectors is the heart of controlling both viruses.
Nutrient deficiencies and correction
A well-nourished onion crop resists pests and diseases better, and much of what looks like disease is actually a nutrient disorder. Always base fertiliser decisions on a soil test — too much nitrogen makes the crop succulent and prone to thrips and rots, while too little stunts growth.
| Nutrient | Deficiency symptoms | Correction |
|---|---|---|
| Nitrogen | Yellowish-green, erect, curled, wilted, dwarf leaves; soft tissue above the bulb at maturity | Foliar spray urea 1% or DAP 2%, twice at weekly intervals |
| Phosphorus | Slow growth; light-green leaves; tip burn on older leaves; few dried outer scales | Soil-apply recommended P at sowing; foliar DAP 2% twice at fortnightly intervals |
| Potassium | Tip burn; dark-green, erect leaves; bolting; older leaves yellow and necrotic | Foliar K2SO4 @ 1%, twice at weekly intervals |
| Sulphur | General, uniform chlorosis including young leaves | Foliar K2SO4 or CaSO4 @ 1%, twice at fortnightly intervals |
| Manganese | Tip burn, light-coloured, curling leaves; delayed bulbing with thick necks | Foliar MnSO4 @ 0.3%, twice at fortnightly intervals |
| Zinc | Interveinal necrosis; young leaves yellow with pitting on mature leaves | Foliar ZnSO4 @ 0.5%, twice at fortnightly intervals |
| Iron | Interveinal chlorosis of the youngest leaves, progressing to bleached leaves | Foliar FeSO4 @ 0.5% |
Physiological disorders such as rubberification and premature sprouting of bulbs occur in low-lying, over-irrigated fields and with high nitrogen (especially as urea); balanced nutrition, including zinc sulphate and ammonium molybdate, and avoiding excess water and late harvest help control them.
Crop-stage-wise IPM calendar
| Crop stage | IPM practice |
|---|---|
| Pre-sowing | Do a soil test and apply nutrients accordingly. Add well-rotted FYM @ 10 t/acre (incorporated 2-3 weeks before transplanting) or vermicompost @ 4 t/acre (one week before). Deep-plough in summer, adopt the stale seedbed technique or soil solarisation (45-gauge/0.45 mm polythene for three weeks) to cut weeds and soil-borne pests, and keep bunds weed-free. |
| Sowing / planting | Treat seed/seedlings with Azotobacter and PSB cultures @ 240 g each/acre and with Trichoderma spp. and Pseudomonas fluorescens. Apply NPK @ 40:20:40 kg/acre — one-third N, the entire P and 60% K as a basal dose. For heavy weed pressure, spray oxyfluorfen 23.5% EC @ 170-340 ml in 200-300 l of water/acre as a pre-plant application, or quizalofop-ethyl 5% EC @ 300-400 ml in 150-180 l of water/acre 20 days after planting, followed by a hand weeding if needed. |
| Vegetative stage | Apply the second one-third of N at 21 days and the last one-third at 45 days after transplanting, with the remaining 40% potash top-dressed at 21 days. Keep the crop weed-free for the first 30-45 days. Begin weekly AESA field scouting from establishment, selecting five spots and five plants each, and act on the P:D ratio. Install blue sticky traps @ 4-5/acre for thrips, pheromone traps @ 4-5/acre for caterpillars (change lures every 2-3 weeks), light traps @ 1/acre (operate 6-10 pm), and bird perches @ 20/acre. Installing Fyllo Smart Sticky Traps at this stage automates the daily counting of thrips and other flying pests and sends threshold alerts through the Fyllo App, so sprays are timed to real field numbers rather than the calendar. Release Trichogramma pretiosum @ 40,000/acre weekly from flower initiation if caterpillars are active. |
| Reproductive / bulb stage | Apply the third N dose (13.33 kg N/acre) at 60 days after transplanting. Remove damaged leaves, rogue diseased plants, and continue the same insect and disease management as the vegetative stage. Correct any nutrient deficiency based on soil test and leaf symptoms. |
| Harvest and post-harvest | Harvest when the tops begin to yellow and fall over, lifting bulbs gently without bruising the outer scales. Cure bulbs at 30-45°C and 60-75% RH for 1-4 days until the necks brown, cut necks to about an inch, and store in a cool, dry place to prevent the storage moulds and bacterial rots described above. |
Natural enemies and their conservation
Protecting the natural enemies already present in the field is the most cost-effective first line of defence. Onion's key defenders include the parasitoids Ceranisus menes (thrips), Trichogramma, Tetrastichus, Telenomus, Campoletis chlorideae, Chelonus blackburni and Bracon spp. (caterpillars) and Aphaereta pallipes (onion maggot); and predators such as ladybird beetles, green lacewings (Chrysoperla zastrowi sillemi), hover flies, minute pirate bugs (Orius spp.), predatory thrips and mites, spiders, praying mantis, ground and rove beetles, and birds like king crow and common mynah.
To conserve them:
- Avoid broad-spectrum sprays when the P:D ratio is favourable (the general rule is 2:1).
- Grow flowering insectary plants such as sunflower, marigold, buckwheat, cowpea, coriander, mustard and alfalfa on borders and bunds.
- > Do not uproot nectar-source weeds like Tridax and Ageratum*.
- Add organic matter and reduce tillage to protect below-ground defenders.
- Never spray chemicals within seven days of releasing parasitoids.
Fyllo Smart Sticky Traps and the Fyllo App
Onion IPM asks growers to watch thrips numbers closely, time sprays correctly, rotate chemicals and adjust nutrition by crop stage — a lot to track by hand. Fyllo Smart Sticky Traps make the monitoring part automatic. The traps use AI-based image recognition to identify and count the flying pests that land on them — especially onion thrips, along with aphids and small moths — and sync the data to the Fyllo App, so growers see live pest counts without checking cards in the field every few days. When numbers cross the threshold, the app sends an alert naming the pest, the recommended spray chemical, the quantity and the schedule.
The app also helps with crop-stage spray planning, chemical rotation to slow resistance, and soil-test-based nutrient recommendations. Sticky traps monitor flying insects only; soil pests like onion maggot, mites, bulb rots and viral diseases still need the cultural and biological measures above. See how this fits into onion crop management.
Key takeaways for onion growers
- Thrips are the number-one pest. Scout weekly, use blue/sticky traps, prefer sprinkler irrigation, avoid excess nitrogen, and spray only when the threshold and P:D ratio call for it.
- Manage the vectors to manage the viruses. Iris yellow spot and onion yellow dwarf are controlled mainly by keeping thrips and aphids down with healthy transplants and trap-based monitoring.
- > Start clean in the nursery. Raised beds, solarisation, thin sowing and Trichoderma/Pseudomonas* seed treatment prevent damping-off, which can take 60-75% of seedlings.
- Cure and store carefully. Most black mould, green mould and bacterial rots are decided at harvest — dry bulbs well, discard damaged ones, and store cool and airy.
- Feed by soil test and rotate chemicals. Balanced nutrition keeps the crop resistant, and rotating insecticide and fungicide classes prevents resistance build-up.
Conclusion
Onion rewards steady, season-long attention more than any single spray. By combining good nursery hygiene, resistant varieties, regular AESA scouting, trap-based monitoring, conservation of natural enemies, need-based chemical use and careful curing, growers can protect both yield and bulb quality. Always follow the product label for dose, timing and pre-harvest interval, and consult your local KVK or agricultural university for region-specific advice. Tools like Fyllo Smart Sticky Traps and the Fyllo App can make the monitoring and decision-making simpler, smarter and more affordable.
