Editor’s Note
This article is part of the Insect Netting Knowledge Series, focusing on onion, garlic, and leek protection against thrips and virus transmission.
For mesh physics and ventilation principles, visit the Insect Netting Hub Page.
Introduction
When Jorge, an onion grower in Peru, noticed silver streaks appearing across the leaves of his early-season onions, he knew exactly what it was—thrips. Within weeks, the plants weakened, bulbs became lighter, and harvesting projections dropped nearly 30%. Sprays did little. The insects hid deep inside the leaf sheaths, untouched by chemicals.
It wasn’t until he switched to 50 mesh insect netting—reinforced with red photoselective netting—that thrips numbers finally collapsed, and bulb weight rebounded.
Stories like Jorge’s are now common worldwide. Thrips is one of the hardest pests to control with pesticides, but one of the easiest to suppress with well-designed insect netting.
This guide explains exactly how onion, garlic, and leek growers can use mesh size, red photoselective nets, and ventilation design to stop thrips while protecting crop health and yield.
Why Onions, Garlic & Leeks Need Insect Netting
Thrips causes severe economic losses
Thrips damage isn’t superficial—it directly reduces crop physiology and yield:
- Scraping of leaf tissue → silvering, curling
- Reduced photosynthetic efficiency
- Weak plants more vulnerable to stress
- Bulb weight drops 20–45% under severe infestation
- Leek marketability drops due to cosmetic scars
Expert Insight
Thrips populations explode under warm, dry conditions, making netting an essential barrier during peak pressure periods.
Thrips is a major virus vector (the real threat)
Onions, garlic, and leeks are susceptible to several thrips-transmitted viruses:
- Iris Yellow Spot Virus (IYSV)
- Tomato Spotted Wilt Virus (TSWV)
- Other Orthotospoviruses affecting allium species
Sprays cannot stop virus transmission. Only physical exclusion—insect netting—prevents infection.
Why chemicals fail against thrips
- Thrips hide between leaf sheaths where sprays cannot reach
- Rapid reproduction → fast resistance development
- Hot climates reduce spray persistence
- Spray intervals become too frequent and costly
Want to reduce sprays and stabilize bulb yield?
Request a Thrips Netting Consultation
Thrips Biology & Mesh Size Selection
Thrips body width defines mesh selection
Thrips are tiny—one of the smallest pests in vegetable systems.
| Parameter | Measurement |
| Thorax width | 0.19–0.25 mm |
| Body length | 1.0–1.5 mm |
| Behavior | Easily carried by wind into structures |
Key Interpretation
To exclude thrips, mesh aperture must be ≤0.25 mm, which corresponds to 50–75 mesh depending on yarn size and tension.
Which mesh sizes work for allium crops?
| Mesh Size | Aperture (approx.) | Thrips Exclusion | Notes |
| 40 mesh | ~0.45 mm | Limited | Often insufficient for onions |
| 50 mesh | ~0.32–0.35 mm | Strong | Recommended standard |
| 75 mesh | ~0.20 mm | Very strong | For vents & virus-hotspots only |
Expert Insight
Allium crops require finer mesh than most vegetables because thrips pressure is especially high in dry, windy seasons.
Warning
Finer mesh increases temperature—ventilation must be engineered properly.
The Red Net Advantage (Photoselective Anti-Thrips Technology)
Red insect netting has become one of the most successful thrips-reduction technologies in Allium crops.
Why red nets work (light spectrum behavior)
Research shows thrips respond strongly to light wavelengths:
- Red / far-red light disrupts thrips landing and settling behavior
- Red light alters insect orientation and reduces feeding time
- Photoselective nets diffuse light → stronger leaf color and thicker cell walls
Grower Benefit
Red nets do not replace mesh size, but enhance thrips repellency, giving 30–60% fewer thrips even with the same mesh aperture.
Red nets vs transparent nets（Performance Comparison）
| Feature | Transparent Net | Red Net |
| Thrips abundance | High | Reduced 30–60% |
| Virus incidence | Medium–High | Lower |
| Leaf color & vigor | Normal | Stronger greens, better turgor |
| Light diffusion | Standard | Higher |
| Stress tolerance | Basic | Slight improvement |
Expert Interpretation
Red nets shine in high-light regions such as the Middle East, Peru, Mexico, and Australia.
Real-world results（Red net case summary）
- Onion growers using red nets reported fewer thrips and stronger leaf architecture
- Garlic farmers observed lower IYSV infection rates
- Leek growers saw cleaner leaves and fewer cosmetic scars
- In dry windy valleys, red nets reduced wind-borne thrips landings dramatically
Want to test red netting for your allium crops?
The Heat Problem: Fine Mesh Raises Temperature
Because thrips require 50–75 mesh for exclusion, growers must manage the downside: reduced airflow.
How temperature affects onion, garlic & leek performance
High temperature causes:
- Faster thrips reproduction
- Bulb initiation stress
- Lower bulb weight
- Higher evapotranspiration
- Premature leaf senescence
Ventilation loss as mesh becomes finer
| Mesh Size | Airflow Reduction | Temperature Rise |
| 25 mesh | ~0% | +0°C |
| 40 mesh | 20–25% | +1°C |
| 50 mesh | 35–45% | +2°C |
| 75 mesh | 50%+ | +3–4°C |
Expert Insight
Because allium crops are relatively heat-sensitive during bulb formation, 50 mesh must always be paired with good ventilation design.
The Dual-Zone Mesh System (Industry Standard for Thrips Exclusion)
To balance exclusion with temperature, most commercial allium growers use a dual-zone design.
Roof mesh: 25–32 mesh（Cooling priority）
The roof must release heat quickly.
- Prevents thermal stress
- Maintains leaf turgidity
- Reduces virus susceptibility
Warning
Do NOT use 50 mesh on the roof.
Sidewalls: 50 mesh（Thrips exclusion zone）
This is the barrier that stops the majority of thrips entering.
Vents, doors & windward sides: 75 mesh
These are high-risk entry points.
Expert Insight
Thrips do not “choose” to enter—they are blown in by wind. So wind-facing vents must always receive finer mesh.
Where to use red netting?
- As full sidewall coverage
- As supplemental panels on windward sides
- As wrap-around bands near canopy height
- In areas with extreme thrips pressure or virus history
Need help designing a dual-zone thrips-proof structure?
Recommendations for Different Production Systems
Open-field allium production
- Use 50 mesh red or transparent nets as overhead row covers
- Secure edges to prevent thrips entry from below
- Best for early-season or virus-sensitive crops
Low tunnels / high tunnels
- Roof: film
- Sidewalls: 50 mesh
- Windward vents: 75 mesh
- Optional red net panels
Benefit: Perfect balance for spring–summer onion crops.
Full net-houses（High-value garlic / onion seed production）
- Roof: 25–32 mesh
- Sidewalls: 50 mesh
- Doors & vents: 75 mesh
- Best for large, continuous, commercial production blocks
Expert Insight
Seed garlic and seed onion grades benefit most from sealed structures—virus pressure must be near zero.
Installation Guidelines That Actually Stop Thrips
Seal the base completely
Thrips often crawl in from the soil surface.
Reinforce wind-facing walls
Place 75 mesh panels or red nets to block wind-borne thrips.
Use a double-door airlock
Prevents thrips from entering during harvest operations.
Repair small tears immediately
A 1 cm tear can allow thousands of thrips into a field.
Need installation accessories? Clips, hooks, tensioners available
IPM Integration: Netting + Agronomy
Using netting alone delivers strong thrips control, but integrating agronomy practices brings results to 90–95%.
Key IPM practices:
- Yellow sticky traps for monitoring
- Manage nitrogen to avoid overly tender leaf tissue
- Remove nearby weeds (alternative hosts)
- Maintain soil moisture—thrips dislike humidity
- Use reflective mulch if available
- Field scouting every 3–4 days
Expert Insight
Netting reduces invasion—but IPM reduces population pressure, producing a more stable system.
Conclusion
Thrips is one of the most difficult pests to control in onions, garlic, and leeks—especially because it causes both direct feeding damage and serious virus transmission. Chemical control frequently fails, making insect netting the most reliable, long-term solution.
The most effective system combines:
✔ Mesh size (50 mesh standard; 75 mesh for vents)
✔ Dual-zone net-house design
✔ Red photoselective netting for behavioral suppression
✔ Proper installation and sealing
✔ Strong ventilation engineering
✔ IPM practices
When implemented together, growers can dramatically reduce thrips populations, minimize virus pressure, and protect yield and bulb quality throughout the season.
Want mesh recommendations or a custom allium net-house design?
Request a Free Agronomy Consultation
FAQ — Insect Netting for Onion, Garlic & Leeks
What mesh size is best for controlling thrips in onions and garlic?
50 mesh is the recommended standard because its aperture is small enough to block thrips while still allowing manageable airflow. In high-risk regions or areas with strong viral pressure, 75 mesh should be used on vents and wind-facing walls for added protection.
Does insect netting increase temperature in allium crops?
Yes—finer mesh reduces ventilation and can increase temperature by 1–3°C depending on climate. Because onions and garlic are sensitive during bulb formation, growers should always pair 50 mesh sidewalls with 25–32 mesh roofs to release heat efficiently.
Why is red insect netting effective against thrips?
Red nets alter the light spectrum in ways that disrupt thrips’ ability to locate and settle on host plants. Studies and field reports show a 30–60% reduction in thrips on crops covered with red nets. They are especially effective in high-light regions where visual cues dominate insect behavior.
Can insect netting reduce virus incidence such as IYSV or TSWV?
Yes. Thrips are the vector for these viruses, and preventing their entry dramatically reduces infection risk. Netting cannot cure infected plants, but it prevents new infections from occurring—especially important in garlic seed and onion seed production.
What structure design works best for onion and garlic growers?
Dual-zone net-houses perform best: roof (25–32 mesh), sidewalls (50 mesh), vents (75 mesh). This setup balances cooling, thrips exclusion, and airflow stability. Low tunnels also work well for early-season protection.
Can insect netting replace pesticides entirely?
In many regions, yes—netting can reduce thrips pressure by 85–95%, allowing growers to greatly reduce chemical use. However, pairing netting with IPM improves long-term stability and delays resistance development in nearby populations.
