Thrips are tiny creatures that have a huge ability of causing havoc in green houses. They feed on plant sap, leave silvery spots, and even cause the leaves to wither.  Due to their size, they hide well  in flowers, buds, on leaf underside and in the soil. It is therefore  important to detect an infestation early to avoid further damage. 

Here are some of the best methods to monitor thrips in greenhouse crops. Think of “monitoring” as detective work: you’re always looking, watching, recording, and using clues to decide when to act.

1. Sticky Traps (Yellow, Blue, Hot-Pink, etc.)

Sticky cards or traps are one of the most useful, low-cost ways to monitor thrips.

• Color matters: Thrips are attracted to certain colors. Yellow and blue sticky cards often work well. Hot-pink cards sometimes attract even more, especially for certain species.

• Placement: Put traps just above or at canopy height. Also near vents, doors, and entry points where thrips might enter.

• Density / frequency: One or two traps per 1,000 square feet (≈ 90-100 square meters) is common; in large greenhouses, spread them out evenly. Inspect them weekly, count how many thrips are caught, and record trends.

Traps give early warning. They don’t catch every thrip, but they tell you whether there’s a problem when you can still respond cheaply.

2. Visual Inspection / Scouting

Sticky traps catch flying adults. But many thrips live hidden among leaves, buds, or soil. So direct plant checking is essential.

• Hand-lens or magnifier: Use a 10×-20× magnifying glass. This helps you see tiny larvae, eggs, and damage spots.

• Inspect new growth, flowers, buds: Thrips love tender parts of plants. Open flowers often hold them. Buds sometimes hide them so well you need to gently open to inspect.

• Tap test: Tap flowers or leaves over a white sheet of paper to dislodge thrips. They fall and you can see them moving.

Do scouting regularly, at least once a week. More often if you’ve had trouble with thrips before. Keep records: number of thrips, location in greenhouse, plant type. Trends are more important than one-off counts.

3. Indicator Plants

Sometimes certain plants show damage earlier than your main crop. These are called indicator plants.

• Petunias are often used as indicator plants for Western Flower Thrips (WFT), because damage or virus symptoms show more quickly on them.

• Put a few indicator plants in spots around the greenhouse: near doors, vents, or among the main crop benches. Inspect them carefully. If you see thrips there, you might act across the greenhouse soon.

4. Environmental & Physical Monitoring

Thrips’ life stages include ones that live off the plant (soil or growing medium), sometimes in pupal stages. So paying attention to the environment and structure helps.

• Soil / growing medium checks: Pupae often drop to soil or growing medium. Checking soil or under mats, benches, or pots for pupal stages or dead leaves helps.

• Screens / mesh barriers: Using fine mesh (microscreening) on vents, doors to keep thrips out is very effective.

• Sanitation: Keep greenhouse clean. Remove weeds, plant debris, old crop materials. Weeds near vents or outside can harbour thrips. Fallen leaf litter gives places for pupae and eggs.

5. Technological / New Methods

Modern tools are helping make monitoring faster and more precise.

• Computer vision / image analysis: There are recent studies using cameras and deep learning to automatically detect and count thrips. These tools can reduce labor time and spot patterns humans might miss.

• Digital magnifiers / apps: Using smartphone cameras with magnifying lenses, or using apps that assist in damage detection or insect counting helps small growers or those without lab gear.

6. Thresholds & Decision Points

Monitoring is only useful if you act when needed. That means setting thresholds: how many thrips per trap, or how much damage, triggers action.

• For some crops, 5 thrips/trap/week is a threshold; for others, 20 thrips/trap/week. It depends on how sensitive your crop is, what damage you consider acceptable.

• Use graphs of trap catch numbers over time to see whether thrips population is rising or falling. If rising, act early so damage doesn’t escalate.

7. Putting It All Together: Integrated Monitoring Plan

Here’s how you might combine those methods into a full plan:

Task	Frequency	Tools / Methods
Weekly trap check and count	Once per week	Sticky cards at canopy height and near entry points
Weekly visual inspection	Once per week (more often for sensitive crops)	Hand lens, tap test, inspection of buds/flowers
Check indicator plants	Weekly	Inspect very carefully, record findings
Soil / medium inspection	Bi-weekly or monthly	Look under pots, benches
Record keeping	Every monitoring event	Table/chart of trap counts, visual findings, damage signs
Threshold review	As needed (when trap counts high or damage seen)	Decide control actions: biological, cultural, chemical

 

Why Monitoring Is Exciting (Yes, Exciting!)

• It gives you early warning, so you can act before big damage happens. Less panic, more control.

• You start to see patterns: when thrips spike (maybe after a warm spell, or when a new crop comes in), where hotspots are (corners, vents, certain benches).

• You avoid overusing pesticides because you only spray when you need to. This saves money, protects beneficial insects, and reduces resistance.

• It combines old-school observation with new tech: sticky cards, hand lenses, indicator plants, plus apps and image detection. There’s a detective in every grower!

Final Thoughts

It does not have to be frightening and intimidating to monitor thrips in greenhouse crops. Simple tools such as sticky traps, indicator plants, and frequent visual checks, allow you to detect thrips early. Growers who use protection plus and other smart strategies often avoid large crop losses, and get healthier plants.

Early detection implies that you are able to address smaller infestations easier, which results in using fewer sprays, less damage, and overall, fewer costs.