Greenhouse Pest Management: Prevention, Scouting and IPM

Integrated pest management (IPM) is a decision process: prevent avoidable introductions, monitor consistently, identify the cause, decide when action is needed, choose compatible controls, and check the result.

This page does not prescribe universal trap densities, action thresholds, biological-control release rates, humidity limits, or pesticide rotations. Those details depend on the crop, pest, climate, production goal, local registration, and chosen beneficial organism or product. Use current extension guidance, product labels, and qualified local help for the specific situation.

1. Start clean and reduce entry points

Inspect plants, cuttings, media, containers, and packaging before they enter the main crop. Separate incoming material where practical and monitor it before release. Keep doors closed when not in use, repair glazing and screen gaps, and control weeds inside and near the structure.

Fine insect screens can reduce airflow. UC IPM notes that a ventilation system may need modification when fine mesh is installed, so include screen resistance in ventilation planning.

2. Make sanitation a written routine

Remove crop debris and severely affected material in a way that does not spread pests through the greenhouse. Clean soil and organic matter from tools, benches, trays, and surfaces before using a disinfectant, and follow the product label for surface compatibility, concentration, contact time, rinsing, and worker safety.

Do not move tools, carts, clothing, or reusable containers from an affected area to a clean area without the planned sanitation step.

3. Build a repeatable scouting route

Use a greenhouse map and inspect the same zones on a regular schedule. Include:

• new growth and leaf undersides;
• flowers and buds where thrips may hide;
• media surfaces and drainage areas;
• plants near doors, vents, and incoming-material areas;
• weak, discolored, distorted, or sticky tissue; and
• recurring hot spots shown by earlier records.

A hand lens can help, but photographs or physical samples may be needed for a reliable diagnosis. Record “no pest observed” as well as detections so gaps in scouting are visible.

4. Use sticky traps for trends, not as the whole diagnosis

Sticky cards can help detect and compare some flying adult insects. Number each card, map its location, keep placement consistent, record the date, and identify catches as specifically as practical.

Cards do not represent every pest or life stage. Aphids, mites, immature whiteflies, soil organisms, and diseases require direct crop or media inspection. Choose card density, color, and placement from crop- and pest-specific guidance.

5. Identify the organism before choosing a control

Abiotic injury, nutrient disorders, root problems, chemical damage, and several pests can look similar. Before treatment, document:

• the plant species, cultivar, and growth stage;
• where symptoms began and how they spread;
• recent irrigation, fertilizer, pesticide, and environment changes;
• the pest or symptom on multiple plants; and
• roots, media, and drainage where relevant.

Use an extension diagnostic service or qualified laboratory when identification remains uncertain. A treatment chosen for the wrong cause can delay the real fix or damage the crop.

6. Establish a local action threshold

An action threshold is the point at which the expected harm justifies a control step. It changes with crop value, cosmetic tolerance, pest biology, virus risk, production stage, market requirements, and the time a control needs to work.

Begin with published guidance for the crop and pest, then refine it from consistent local records. Do not copy a commercial-floriculture threshold into a food crop or hobby greenhouse without checking its context.

7. Correct environmental and cultural contributors

Excess moisture, poor drainage, dense canopies, weeds, overfertilization, plant stress, and stagnant zones can contribute to problems. Fixing those conditions may support other controls, but it does not replace pest identification.

Avoid extreme environment changes that stress plants or conflict with crop requirements. Use measured conditions and the greenhouse ventilation guide when airflow or condensation is part of the problem.

8. Use biological controls with supplier-specific instructions

Predatory mites, parasitoids, nematodes, and other beneficial organisms differ in target pest, life stage, release timing, temperature and humidity needs, storage, and compatibility with pesticide residues.

Confirm the pest identity and follow the current supplier program for the crop and pressure. Record organism, batch, release date, location, environmental conditions, and follow-up observations. “Natural” does not mean that any beneficial will work in any greenhouse.

9. Follow pesticide labels and protect workers

Use only products registered for the site, crop, and target pest in the relevant jurisdiction. The label governs dose, application method, personal protective equipment, restricted-entry interval, preharvest interval, environmental precautions, and maximum applications.

Resistance-management groups can inform a rotation, but the label and a current crop-specific program still control. Do not improvise tank mixes or assume that different brand names use different modes of action. Consider compatibility with pollinators and biological controls.

10. Verify the result

Schedule follow-up scouting before applying a control. Compare the same plants, zones, and traps, and record crop injury, beneficial activity, pest stage, and trend. If the population does not respond, reassess identification, coverage, timing, resistance, environment, and reinfestation rather than simply repeating the same action.

Simple scouting record

| Field | Record | | --- | --- | | Date and scout | Who inspected and when | | Zone, bench, and crop | A consistent mapped location | | Pest or symptom | Identification and confidence level | | Count or severity | Same method each visit | | Crop stage | Seedling, vegetative, flowering, harvest, or other | | Recent changes | Plants, irrigation, environment, nutrition, or treatments | | Action | What was done, where, and under which instructions | | Follow-up date | When the result will be checked |

Official references

• UC IPM: Integrated pest management for floriculture and nurseries
• UC IPM: Floriculture and ornamental nursery pest guidelines
• UC IPM: Thrips identification and management
• U.S. EPA: Agricultural Worker Protection Standard

Consistent records turn pest management from a reaction into a process. Start with prevention and scouting, make the smallest justified intervention, and verify what happened before the next decision.