Aphids
Overview
Aphids are one of the most common pest groups in horticulture.
They feed on plant sap and are strongly associated with:
- soft growth
- high nitrogen
- protected crops
- mild conditions
- dense canopies
- young shoots and growing points
Aphids are important because they can:
- distort growth
- produce honeydew
- reduce crop quality
- spread viruses in some crops
- disrupt biological control programmes if allowed to build
Identification
Aphids are soft-bodied insects found in colonies.
They may be:
- green
- black
- yellow
- pink
- grey
- brown
Look for:
- colonies on young shoots
- curled leaves
- sticky honeydew
- white cast skins
- ants
- distorted growing points
- winged aphids
Winged aphids are an important early warning sign of movement into or around the crop.
Damage symptoms
Typical symptoms include:
- curled leaves
- distorted shoots
- stunted growth
- sticky leaves
- sooty mould
- flower contamination
- poor visual quality
- reduced vigour
Damage is often worst on soft new growth.
Conditions favouring aphids
| Condition | Risk |
|---|---|
| Soft rapid growth | Very High |
| Excess nitrogen | High |
| Mild protected conditions | High |
| Dense canopy | Moderate |
| Low predator activity | High |
| Weed reservoirs | Moderate–High |
| Crop carryover | High |
Monitoring
Inspect:
- growing points
- undersides of young leaves
- flower stems
- crop edges
- soft flushes of growth
- weeds near the crop
Check for:
- winged aphids
- early colonies
- honeydew
- cast skins
- mummified aphids
Aphid mummies can show parasitoid activity.
Hotspot behaviour
Aphids often start in small colonies.
Common hotspot areas include:
- soft growth zones
- crop edges
- near doors and vents
- warm sheltered areas
- stressed plants
- weeds
- old crop residues
Early colonies should be mapped and revisited.
Biological control strategy
Aphid biological control usually works best when started early.
Useful strategies include:
- parasitoid wasps
- predatory midges
- lacewing larvae
- ladybirds where suitable
- banker plant systems in some crops
- preserving naturally occurring predators
Biological control is harder once colonies become dense and curled leaves protect aphids.
Crop balance and nutrition
Aphids are strongly influenced by crop growth balance.
High soft growth can increase risk.
Useful crop-management actions:
- avoid excessive nitrogen
- avoid overly soft vegetative growth
- maintain balanced irrigation
- reduce crop stress
- avoid repeated disruption of natural enemies
Commonly affected crops
Related BioWiki pages
Key message
Aphid management is easiest before colonies become dense.
Find winged aphids and early colonies quickly, protect natural enemies and avoid producing excessively soft growth.