Aphids on broccoli© Fir0002
'Aphids' is a generic term for over 500 species (in the UK) of sap-sucking insects which secrete honeydew. The moulds that often grow on this are unsightly, but generally harmless. However, the aphids do weaken plants and distort growth and leaves. More seriously, aphids transmit many viruses and the physical wounds they cause encourage further infections.
- Distorted growth & leaves
- Discarded white exoskeletons on tops of leaves
- Sooty and/or sticky patches on leaves
- Presence of ants which may protect the aphids in return for the honeydew they produce
Prevention & control
- The first defence is to choose resistant varieties and don't over-apply nitrogenous fertilizers as these encourage sappy growth which is attractive to aphids.
- You can also grow under horticultural fleece or enviromesh to physically prevent attack.
- Next, encourage aphid predators such as ladybirds, earwigs, spiders, bluetits, lacewings and hoverflies.
- On trees, remove protection provided by ants and increase predation by natural enemies by applying a band of grease or glue around the trunk to prevent ants getting to the aphids.
- If this doesn't keep them at bay, rub them off between thumb and forefinger or pick off infested leaves and shoots.
- If you do feel you need to spray, use derris, pyrethrum or insecticidal soap but bear in mind that this may well also kill off the beneficial insects that can prevent repeat infestations.