Sierra Greenhouse Insights

Greenhouse Pest Management: Complete Guide to Prevention & Control (2025)

By Sierra Greenhouse Experts14 minutes
Greenhouse pest management techniques demonstration with natural control methods
Greenhouse pest management techniques demonstration with natural control methods

Effective pest management keeps crops saleable, staff safe, and operating costs predictable. This production-grade guide turns the bullet list into a practical playbook with exact scouting routines, action thresholds, and control tactics you can run tomorrow morning.

Quick Wins (do these this week)

  • Number and map sticky cards; one card per 1,000 sq ft (minimum) and extras at doors/vents; raise to 1 per 1,000 sq ft for whitefly-prone crops and at least 1 per house for small spaces.
  • Start a weekly 30–45 min scouting loop with a 10–20× hand lens. Log counts by card ID and crop bench.
  • Quarantine all new plant material for 7–10 days; scout and treat before it enters production.
  • Drop overnight RH peaks: late‑day heat + vent; target canopy RH <85–90% and <8–12 hours continuous leaf wetness.
  • Standardize pesticide/bio rotations by IRAC (insecticides) and FRAC (fungicides) codes; never repeat the same code on successive generations.

Table of Contents

Understanding Greenhouse Pests

Pests arrive three ways: on incoming plant material, through openings (doors, vents), and via people/tools. Once inside, warm temperatures, dense canopies, and high humidity accelerate reproduction cycles. A basic rule: anything that increases canopy humidity, reduces airflow, or introduces uninspected plant material increases risk.

Insects & Mites: aphids, whiteflies, spider mites, thrips, fungus gnats, shore flies, leafminers, scale.

Diseases: Botrytis (gray mold), powdery mildews, downy mildews, root rots (Pythium/Phytophthora), leaf spots.

Other Pests: slugs/snails, rodents, birds, plant‑parasitic nematodes.

Prevention Strategies

Cultural Controls

  • Sanitation program: Remove plant debris daily (not to in‑house trash). Power‑wash and disinfect empty houses between crops; clean benches, floors, tools, and irrigation lines. Pre‑clean first (debris reduces disinfectant efficacy), then disinfect. Maintain weed‑free perimeters to break “green bridges.”
  • Environmental management: Maintain consistent airflow (HAF fans), avoid RH spikes at dusk/dawn with timed heat‑and‑vent cycles, and keep canopies pruned and spaced for air movement and spray coverage. Fix drainage; avoid algae.
  • Plant health: Feed to crop targets; avoid excess N that drives soft, pest‑attractive growth. Scout susceptible cultivars first.

Physical Barriers & Exclusion

  • Screening: Fit insect screens on vents/sidewalls sized to the smallest target (e.g., ~100 mesh for western flower thrips). Seal gaps, weather‑strip doors, and use self‑closing hardware.
  • Quarantine: Isolate incoming plugs/liners for 7–10 days; place indicator plants and sticky cards; treat and re‑inspect before release to production.

Monitoring and Detection

Sticky cards are your early‑warning system—and your dataset.

  • Density & placement: Minimum 1 card/1,000 sq ft, plus cards at doors and vents; for whitefly‑susceptible crops, increase density (up to ~1/1,000 sq ft across the house). Maintain at canopy height and keep locations consistent. Number every card.
  • Weekly routine: Inspect all cards and a fixed sample of plants/benches each week. Use a 10–20× lens for mites/thrips. Record counts by pest and card ID; graph trends.
  • Targeted plant scouting: Open flowers for thrips, flip leaves for mites/whiteflies, check media surface for fungus gnats/shore flies.

Pro tip: Make one house‑map with card IDs. If a card spikes, you immediately know which bench and crop to inspect and treat.

Action Thresholds

Use thresholds to switch from monitoring to action. Thresholds vary by crop and tolerance; tune these with your own history.

| Pest | Typical monitoring threshold (per card per week, per ~1,000 sq ft) | When using biocontrols | | --------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------- | | Western flower thrips | Start investigating around 10–15; highly sensitive crops <10; low‑sensitivity crops may tolerate 30–40 | Begin predator releases when ≥2 thrips/card/week are detected | | Whiteflies | No universal trap threshold; treat based on leaf inspections (adults/immatures per leaf) and trend; increase card density on susceptible crops | Begin Encarsia preventatively on at‑risk crops; escalate with rising scale parasitism targets | | Aphids | Treat when colonies first appear; focus on growing tips and undersides | Start Aphidius preventatively on hot spots; combine with bankers where appropriate |

Always integrate visual plant inspections with card counts; traps mostly capture fliers (e.g., thrips, whiteflies) and under‑estimate aphids/mites.

Common Greenhouse Pests

Aphids

What you’ll see: Clusters on tender growth; honeydew and sooty mold; distorted leaves.

Monitor: Focus on new growth and undersides. Card counts under‑represent aphids; use direct inspections.

Controls:

  • Biological: Aphidius colemani (parasitoid) preventatively on melon/green peach aphid; banker plants can stabilize populations. Typical preventive introductions range from ~0.1–3 wasps per 10 ft² weekly; adjust by pressure. Remove or relocate yellow sticky cards near release sites (they catch beneficials).
  • Chemistry: Rotate IRAC codes; avoid consecutive applications from the same code. Spot treat hot spots to preserve beneficials.

Whiteflies

What you’ll see: Adults fly when disturbed; on leaves, check for scales (nymphs) and sooty mold/honeydew.

Monitor: Increase card density on susceptible crops. Check lower leaves for live scales; track percent blackened (parasitized) scales when using parasitoids.

Controls:

  • Biological: Encarsia formosa parasitoid preventatively; common programs begin near 0.1 individuals/ft² weekly, increasing to 0.2/ft² as adults appear; alternatively 1–5 parasitoids per infested plant at 1–2 wk intervals until ~80–90% of scales are parasitized. Maintain 68–77°F and ~50–70% RH during release windows.
  • Chemistry: Use selective materials where possible; rotate IRAC groups. Keep yellow cards away from release zones to avoid trapping Encarsia.

Spider mites (two‑spotted)

What you’ll see: Stippled leaves, fine webbing under stress; thrives in hot, dry microclimates.

Monitor: Tap test over white paper; inspect undersides near veins and lower canopy.

Controls:

  • Biological: Phytoseiulus persimilis is a specialist predator; preventive/low‑pressure broadcasts often start around 0.5–1 predators/ft², increasing to 2/ft² in hot spots. Maintain RH >~70–75% and temps >~68°F for predator performance.
  • Chemistry: Spot treat outbreaks; rotate IRAC groups; avoid materials incompatible with predators.

Thrips (western flower thrips)

What you’ll see: Silvery flecking or streaks on petals/leaf tissue; distorted new growth; vector of tospoviruses.

Monitor: Blue or yellow cards; open flowers. Trend weekly counts.

Controls:

  • Biological: Amblyseius (Neoseiulus) cucumeris or Amblyseius swirskii preventatively (e.g., 25–300 mites/m² per release depending on crop/pressure; slow‑release sachets 1 per 6 ft² as a baseline), plus Orius insidiosus in flowering crops. Layer soil predators (Stratiolaelaps scimitus) against pupae in media.
  • Chemistry: Rotate IRAC codes aggressively; thrips develop resistance quickly. Integrate with sanitation (remove flowers in propagation) and screening (fine mesh on vents).

Natural & Biological Controls

Beneficial insects & mites work best when started early and supported by compatible sprays and sanitation.

  • Release strategy: Start preventatively on crops with a history of issues. Distribute evenly at canopy level; repeat on schedule. Keep yellow sticky cards away from parasitoid release zones; use blue cards for thrips where parasitoids are active.
  • Compatibility: Check IRAC/FRAC codes and product labels for beneficial safety. Oils/soaps can be used tactically but may harm soft‑bodied beneficials—spot test first.

Chemical Control Options

When you must spray, do it precisely.

  • Rotate by Mode of Action: Build rotations by IRAC (insecticides/miticides) and FRAC (fungicides) codes—not brand names—to slow resistance. Avoid back‑to‑back applications from the same code on successive pest generations.
  • Coverage & timing: Calibrate sprayers; spray to glisten, not drip. Time applications to pest life stage (e.g., contact sprays for mobile stages; systemics for hidden feeders). Respect REIs and the EPA Worker Protection Standard.

Integrated Pest Management (IPM)

Implementation Steps

  1. Assessment: Identify pest/disease, crop susceptibility, and pressure. Verify with a lens and samples if unsure.
  2. Plan: Choose cultural/environmental tweaks first; add biologicals; schedule compatible chemistries only if thresholds are exceeded.
  3. Act: Treat hot spots first; preserve refuges for beneficials. Log batch, rate, IRAC/FRAC code, coverage notes, and weather.
  4. Verify: Re‑scout 2–3 and 7 days post‑treatment; adjust rates/rotations; update thresholds per crop.

Disease Control Notes (high‑impact wins)

  • Botrytis (gray mold): Infection risk jumps with RH ≥ ~85–93% and ≥8–12 hours leaf wetness. Reduce overnight humidity with late‑day heat + vent; space/prune for airflow; remove infected tissue before fungicides; rotate FRAC codes.
  • Powdery mildews: Favor warm days/cool nights and high humidity (often >90%) even without free water. Keep humidity steady, avoid big swings, and rotate FRAC groups.

Seasonal Pest Management

Spring

  • Sanitize houses; replace or wash coverings; map and hang sticky cards; start preventatives on historically hot crops.

Summer

  • Watch for mite pressure in hot, dry microclimates; maintain HAF; irrigate early so foliage dries before night; tighten screening on vents.

Fall/Winter

  • Remove all plant material at crop change; warm‑hold empty houses ~2 weeks to flush diapausing pests, then sanitize. Service heaters/vents to manage overnight humidity spikes.

Emergency Response Plans

  1. Confirm & contain: Identify pest/disease; flag benches; isolate severely affected lots.
  2. Knock‑down + protect: Use a fast‑acting compatible material on hot spots; deploy biologicals and environmental fixes house‑wide.
  3. Follow‑through: Rescout 48–72 hours and 7 days later; escalate or step down based on trend lines; update rotation logs.

References

  • UC ANR – Sticky trap monitoring guidelines and densities. https://anrcatalog.ucanr.edu/pdf/21572.pdf ; https://ipm.ucanr.edu/agriculture/floriculture-and-ornamental-nurseries/monitoring-with-sticky-traps/
  • UMass/OK State/MSU – Scouting routines & card placement; 1 card/1,000 sq ft minimum; numbering and mapping. https://www.umass.edu/agriculture-food-environment/greenhouse-floriculture/fact-sheets/ipm-scouting-decision-making ; https://extension.okstate.edu/fact-sheets/ipm-scouting-and-monitoring-for-pests-in-commercial-greenhouses.html ; https://www.canr.msu.edu/resources/greenhouse-insecticides
  • Thresholds for thrips (start at ~10–15/card/week; sensitive crops <10; begin predators at ≥2) and tuning by crop sensitivity. https://gpnmag.com/article/grower-101-pest-counts-and-action-thresholds/ ; https://plant-pest-advisory.rutgers.edu/pest-counts-action-thresholds-in-the-greenhouse/
  • Encarsia formosa whitefly programs and conditions. https://greenmethods.com/encarsia/ ; https://www.hummert.com/encarsia-formosa-pupae-100-3-card-60105400
  • Predatory mites for spider mites and thrips; typical broadcast ranges and performance conditions. https://greenmethods.com/persimilis/ ; https://www.koppert.com/swirski-mite/
  • Botrytis/powdery mildew humidity and leaf wetness drivers; management. https://extension.psu.edu/managing-botrytis-or-gray-mold-in-the-greenhouse/ ; https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019powderymildewsinthegreenhousefinal3-1.pdf
  • IRAC/FRAC rotation frameworks to slow resistance. https://irac-online.org/mode-of-action/classification-online/ ; https://www.frac.info/media/kufnaceb/frac-code-list-2024.pdf
  • EPA Worker Protection Standard (REI & AEZ) overview. https://www.epa.gov/pesticide-worker-safety/agricultural-worker-protection-standard-wps

Key Takeaways

  • Map, number, and trend sticky cards weekly—then act on thresholds.
  • Start biocontrols early and protect them with compatible chemistries.
  • Manage humidity and leaf wetness to suppress Botrytis and powdery mildews.
  • Rotate IRAC/FRAC codes; document every application.
  • Quarantine incoming plant material—don’t import your next outbreak.

Additional Resources

Need expert help with pest management? Contact our specialists for a professional consultation.