Agrodictionary

Aphids in a greenhouse: identification and integrated control

Identify aphids early, map hotspots and combine sanitation, biological control and locally approved treatments in a practical IPM plan.

July 31, 20266 min read

Aphids in a greenhouse: identification and integrated control

Aphids are small, soft-bodied insects that feed on plant sap, often in colonies on growing points and the undersides of young leaves. A colony can build quickly in protected cultivation, but the first response should not be a blind spray. Confirm the pest, map where it occurs and choose measures that protect the crop, beneficial insects and workers.

How to confirm that the pest is an aphid

Use a hand lens and inspect tender shoots, buds and both sides of leaves. Aphids are usually pear-shaped, about 2–4 mm long, and may be green, yellow, grey, brown, black or pink. Most have a pair of small tubes, called cornicles, near the rear of the abdomen. Winged and wingless forms can be present in the same crop.

Do not diagnose from leaf curl alone. Look for living colonies, white cast skins, sticky honeydew and black sooty mould. Ant activity can lead you to hidden colonies because ants feed on honeydew. Severe feeding may cause yellowing, distorted growth and stunting. Some aphid species also transmit plant viruses, so a low insect count can still be important in a young or virus-sensitive crop.

Colonies on growing points or the underside of young leaves.
Sticky, shiny honeydew on leaves or equipment below the canopy.
White cast skins among the insects.
Curled or distorted new growth.
Brown or golden aphid “mummies”, which show parasitoid activity.

Scout the crop, not only the sticky cards

Yellow sticky cards help detect winged aphids, but colonies may already be established before crowded plants produce winged forms. Divide the greenhouse into blocks and inspect a consistent number of plants in each block at least weekly; increase the frequency after new plants arrive or when a hotspot is found.

Record the crop, variety, plant stage, block, number of infested plants, approximate colony size, natural enemies and photographs. Mark the first hotspots so the same plants can be checked again. There is no universal treatment threshold: the decision depends on crop value, growth stage, virus risk, market tolerance and whether the population is rising or falling.

What to do during the first 24 hours

Separate or tag infested incoming plants, remove heavily infested disposable shoots where this is safe for the crop, and place plant waste in a closed container. Check weeds inside and immediately around the structure. Avoid moving workers and tools from an infested block into a clean block without a hygiene step.

Review recent nitrogen applications. Excessive soft growth can favour aphids, so correct a verified imbalance rather than starving the crop. Manage ants where they protect colonies, and avoid a broad-spectrum insecticide that may remove parasitoids and predators and cause a rebound.

Build an integrated control programme

Start with exclusion, sanitation and early detection. Repair gaps, inspect transplants and use insect screening only when the screen area still allows adequate airflow.

As a practical target, fine insect screens (around 50 mesh, effective against many aphids and whitefly) resist airflow enough that vent opening area typically needs to be 2–3 times larger than an unscreened vent to keep the same ventilation rate.

Preserve naturally occurring lacewings, hoverfly larvae, lady beetles and parasitoid wasps.

Commercial biological control may include Aphidius or Aphelinus parasitoids, the predatory midge Aphidoletes aphidimyza, or lacewings. The correct organism, release rate and timing depend on aphid species, crop and climate. Release preventively or at the first small colonies and follow the supplier’s current instructions. Confirm that any pesticide used before or after release is compatible with the beneficial organism.

If a pesticide or biopesticide is necessary, use only a product registered for the crop and location. Follow the label for dose, coverage, personal protection, re-entry and harvest interval. Reach the undersides of leaves, avoid unnecessary repeated applications and rotate modes of action when repeat treatment is permitted. Biological control can suppress colonies, but it may not prevent rapid virus transmission by probing aphids.

Verify the result

Recheck marked plants and neighbouring rows after the interval appropriate to the control method. Compare the number of live aphids and newly infested plants, not only the number of winged aphids on cards. With parasitoids, look for mummies and later for a circular emergence hole.

A successful programme produces clean new growth and a declining hotspot. Old curled leaves and sooty mould may remain after control, so do not treat cosmetic damage as proof that the population is still increasing. If counts do not fall, reconfirm the identification, application coverage, climate and compatibility of the measures used.

Local adaptation: the United States

In the United States, check that every pesticide or biopesticide label includes both the crop and the protected-production use you intend. State requirements may be stricter than the federal label. Record the product, EPA registration details where applicable, rate, treated block, applicator, re-entry interval and pre-harvest interval. In hot regions, insect screens must be sized with enough surface area to preserve ventilation.

Scouting and action checklist

Inspect growing points and leaf undersides with a hand lens.
Map hotspots and record live aphids, mummies and natural enemies.
Quarantine new plants and remove infested waste in a closed container.
Choose sanitation and biological control before disruptive treatments where practical.
Verify local registration, label, re-entry and harvest interval for every product.
Recount the same marked plants and record the result.

The objective is not a one-time knockdown. It is an early-warning loop: observe, identify, act, recount and improve the prevention plan.

Important: Use Gros.farm to keep scouting records, photographs, hotspot locations, treatments and follow-up counts in one production log. The platform supports traceability and team coordination; it does not replace pest identification, the product label or advice from a locally qualified crop-protection specialist.