Thrips Trouble in Ornamentals? What’s Working Right Now in Biological Control

Western Flower Thrips (Frankliniella occidentalis) and Onion Thrips (Thrips tabaci) remain two of the most damaging pests in ornamental greenhouse production. In high-visual-value crops like bedding plants and flowering annuals, even low-level infestations can compromise shipments and erode profits.

This post breaks down what makes thrips so persistent—and how growers can stay ahead, without relying on chemical control as the main line of defense.

Why Thrips Are Difficult to Control in Ornamentals

Thrips thrive in ornamental greenhouses for several reasons:

• Warm, humid conditions accelerate their reproduction

• Flower-dense canopies provide food and shelter

• They hide in leaf undersides, delaying detection

• They transmit viruses like TSWV and INSV

• Spray resistance is growing in many populations

  
  

Takeaway: Chemical-only strategies are falling short as resistant populations develop. A preventive biological approach—targeting multiple life stages—is becoming the new standard.

Which Biological Agents Are Most Effective

Several biocontrol agents have shown consistent results in managing thrips across greenhouse ornamental crops. All are PMRA-registered (Canada) and widely used across North America:

Biocontrol Agent	Targets	Best Use
Neoseiulus cucumeris	Thrips larvae	Cool-season prevention; great for spring bedding plants
Amblyseius swirskii	Thrips & whiteflies	Performs well above 20°C; ideal for summer crops and heated zones
Orius insidiosus	Thrips adults & larvae	Works best in flowering crops; needs daylight and moderate warmth
Beauveria bassiana	Thrips (fungal contact)	Effective in high humidity; ideal as a rotation tool
Dalotia coriaria (Atheta)	Thrips pupae in media	Active in growing media; helps break the lifecycle at the soil stage
Stratiolaelaps scimitus (Hypoaspis)	Thrips pupae in media	Soil-dwelling predator; complements foliar bios by preventing adult emergence

What Leading Growers Are Doing Differently

1. Starting Early

• Bios like cucumeris and swirskii are most effective when applied preventively.

• Sachet systems offer slow-release coverage from transplant onward.

  
  

2. Adapting to Microclimate

• Swirskii thrives at 20°C or higher.

• Beauveria bassiana needs 65–70% RH to perform—misting systems help.

• Environmental sensors allow for better strategy alignment.

  
  

3. Targeting Multiple Life Stages

• Foliar predators like Orius and swirskii suppress adults and larvae in the canopy.

• Atheta and Hypoaspis control pupal stages in the growing media—where thrips often escape foliar bios.

• Layering bios across life stages builds stronger, more sustainable population suppression.

  
  

4. Scouting Weekly

• Use sticky cards + direct crop inspection.

• Log both pest and predator populations.

• Adjust release rates based on conditions—not assumptions.

  
  

5. Tightening Cultural Controls

• Remove weeds, debris, and volunteer plants that harbor thrips.

• Install fine mesh screens on vents and entries.

• Rotate bio-compatible soft chemistries (e.g., insecticidal soaps, B. bassiana) when needed.

  
  

What the Results can Look Like

Impact Area	Benefit
Crop Quality	Fewer visible damage symptoms; higher tray acceptance
Shipping	Better readiness for retail and export schedules
Resistance	Reduced dependence on chemical sprays
Compliance	Alignment with low-residue and organic protocols
Peace of Mind	Predictable outcomes without constant reaction

Best Practice Summary

Don’t...	Instead...
Wait until thrips show up	Start bios at transplant or early crop stages
Use one bio across seasons	Match bios to climate, crop timing, and pest life stage
Rely on sticky cards alone	Combine with visual inspection for accuracy
Expect sprays to fill gaps	Design bios + soft chemistry rotations upfront

Need Help Building a Thrips-Resilient IPM Plan?

At Crop Defenders, we support ornamental growers with:

• Biological selection by crop type, climate, and pest pressure

• Seasonal release planning

• Life-stage-targeted strategies (foliar + soil bios)

• Chemical compatibility review and rotation advice

  
  

Contact Us to schedule a free consultation, and let's co-create a thrips program that's tailored for your greenhouse's unique varieties, location, and growing system.