Pest
Aphids
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Watch for | Watch for in March | Watch for in April | Watch for in May | Watch for in June | Watch for in July | Watch for in August | Watch for in September | Watch for in October |
What it is
Aphids are small, soft-bodied sap-sucking bugs, usually green, black, grey or pinkish, that gather in dense colonies on shoot tips and the undersides of leaves. Hundreds of species occur in Britain and Ireland. Some, such as the black bean aphid, move between hosts over the year, while others, like the lupin aphid, stick largely to one plant.
Symptoms
Look for crowded insects on the youngest growth, with leaves that pucker, curl or turn yellow. Aphids excrete sugary honeydew, so leaves below a colony become shiny and sticky, then blacken as sooty mould grows on the residue. Ants running up and down a stem are a reliable clue, because they farm aphids for honeydew. White flecks on leaves are often just cast skins.
Cause
In spring and summer most aphids are female and give birth to live young without mating, so a colony can multiply within days in mild weather. When plants become crowded, winged forms appear and fly off to new hosts. Many species overwinter as eggs on woody plants, which is why new rose and currant shoots are hit first.
Control
Rub small colonies off with finger and thumb, or blast them away with a jet of water. Pinch out the tips of broad beans once the first pods set, as blackfly cluster there. Leave some aphids for ladybird and lacewing larvae, hoverfly maggots and small birds to feed on; numbers often crash by midsummer. Under glass, parasitic wasps such as Aphidius are available as a biological control. If an infestation is severe, a soap or plant-oil based spray is a last resort; follow the label and avoid spraying open flowers.
Prevention
Grow a mix of flowers that feed hoverflies and lacewings, such as pot marigolds and fennel. Avoid heavy doses of nitrogen fertiliser, which produce soft, sappy growth that aphids love. Check shoot tips weekly from April so you can deal with colonies while they are tiny, and keep ants away from fruit trees with a sticky band.
Plants often affected
Could it be something else?
These problems share some of the same symptoms. Compare them, or run the symptom checker with these signs ticked.
Months to keep an eye out: March, April, May, June, July, August, September and October.
Sources
Identification and life-cycle details were checked against the references below. Text and advice are our own. See our editorial policy.