How to identify and deal with Aphids

Aphids

Aphidoidea

also called Greenfly, Blackfly, Plant lice

Small sap-sucking insects — greenfly, blackfly — that cluster on soft new growth and excrete sticky honeydew. Squash by hand, hose off with water, and encourage ladybirds and lacewings.

Insect Sap-sucker Serious SpringSummerAutumn

How to know it

Pear-shaped insects 1–3 mm long in dense colonies on shoot tips, flower buds and leaf undersides. Green, black, gray, pink or woolly-white depending on the species, mostly wingless with a pair of little exhaust-pipe tubes (cornicles) at the rear; winged forms appear when a colony gets crowded.

What you'll see

Clusters of soft-bodied insects packed along the newest shoots, buds and leaf undersides.
New leaves curl, pucker and distort, and shoot tips grow crooked or stall altogether.
Everything below the colony turns sticky with honeydew, and later black with sooty mold.
White cast skins litter the leaves and look, at a glance, like a second infestation.
Ants patrol the stems — they farm aphids for honeydew and drive the predators off.

Where it comes from

Females give birth to live young without mating through the growing season, so a single overlooked aphid becomes a colony in a fortnight. Winged generations fly to new hosts when numbers rise or the plant is stressed, and most species overwinter as eggs on a woody host — a plum, a spindle, a rose — before flooding back onto soft summer growth.

Worst in warm still spells in late spring and early summer, before the ladybirds and hoverflies have caught up. Soft, sappy growth pushed by heavy nitrogen feeding, plants under glass, and drought-stressed pots are colonized first.

Dealing with it

Rub the colony off between finger and thumb, or knock it off with a hard jet of water — most aphids never find their way back.
Pinch out the infested shoot tip entirely on broad beans and roses; it is the growing point they want.
Leave the ladybird larvae, hoverfly maggots and lacewings alone and give them ten days — they usually finish the job.
Use insecticidal soap or a plant-oil spray only on a colony that is winning, and only in the evening when bees have gone.
Wash off the honeydew before sooty mold settles on it, and deal with the ants that are protecting the colony.

Keeping it out

Feed less nitrogen: sappy forced growth is what the colony is looking for.
Grow open, nectar-rich flowers — dill, fennel, yarrow, calendula, alyssum — so predators are already resident in spring.
Leave hollow stems and seed heads standing over winter for lacewings and ladybirds to shelter in.
Inspect shoot tips weekly from April; five minutes with a thumbnail beats a spray in June.
Check new plants before they join the greenhouse — most indoor outbreaks arrive on a bought plant.

What it goes for

Shoots & stemsLeavesFlowers

Almost nothing is exempt, but broad beans, roses, honeysuckle, cherries, plums, lupins, nasturtiums, brassicas and anything soft under glass carry the heaviest colonies.

and 422 more in the catalog

Trouble it brings with it

Who hunts it for you

Aphid midgeAphidoletes aphidimyza A tiny midge whose orange maggots paralyze aphids and drink them dry, twenty or more each. Sold as a greenhouse biological control and resident outdoors wherever there are small nectar flowers and an unsprayed aphid colony to find. Grow to recruit it: Calendula,Cilantro,Dill,Sweet alyssum,Yarrow
Assassin bugReduviidae A patient ambusher with a curved beak it drives into whatever it catches — caterpillars, beetles, bugs, and the occasional bee, so count it a generalist rather than a specialist. It will jab a careless finger too, so admire it and leave it be. Grow to recruit it: Dill,Fennel,Goldenrod,Sweet alyssum,Tansy,Yarrow
Big-eyed bugGeocoris spp. A stubby 3 mm bug with enormous wrap-around eyes, working the soil surface and the low foliage for aphids, mites, thrips and insect eggs. It is the main natural check on chinch bugs in a lawn and it is killed outright by insecticide. Grow to recruit it: Calendula,Clover,Cosmos,Goldenrod,Sweet alyssum
Damsel bugNabidae A slender, mantis-armed bug that grabs aphids, small caterpillars, and thrips in low crops and meadowy edges. Leave a strip of unmown grasses and flowers for it to overwinter in. Grow to recruit it: Fennel,Sweet alyssum,Yarrow
Dragonflies & damselfliesOdonata Aerial hunters that take mosquitoes, midges and small flies on the wing all day, and whose larvae spend a year or more clearing the same insects from the water. A pond with planted margins and no fish is the way to have them. Grow to recruit it: Bulrush,Iris,Nymphaea,Pickerel Weed
Garden birdsPasseriformes Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray. Grow to recruit it: Echinacea,Elderberry,English holly,Goldenrod,Rudbeckia,Sunflower
Green lacewingChrysoperla carnea Its bristly larvae — "aphid lions" — impale aphids, mealybugs, thrips, and mite colonies, eating hundreds a week. Adults feed on nectar and pollen from small open flowers and overwinter in hollow stems left standing. Grow to recruit it: Cilantro,Cosmos,Dill,Sunflower,Yarrow
HoverflySyrphidae Bee-mimicking flies whose legless larvae graze aphid colonies clean while the adults pollinate. A ribbon of shallow, nectar-rich flowers kept in bloom all season recruits wave after wave of them. Grow to recruit it: Calendula,Chamomile,Fennel,French marigold,Phacelia,Sweet alyssum
Ladybird (lady beetle)Coccinellidae The gardener’s favorite ally: adults and their alligator-shaped larvae each eat thousands of aphids, plus scale, mealybugs, and other soft-bodied sap-suckers. Grow flat, open flowers for the adults and never spray a colony that ladybird larvae are already working. Grow to recruit it: Calendula,Cilantro,Cosmos,Dill,Fennel,Yarrow
Minute pirate bugOrius spp. A pinhead-sized true bug that is the best natural check on thrips, and happily spears aphids, mites, and insect eggs too. It needs pollen when prey is scarce, so keep something flowering nearby. Grow to recruit it: Cosmos,Fennel,French marigold,Sweet alyssum
Parasitic waspsBraconidae & Trichogramma Tiny, stingless wasps that lay eggs in or on caterpillars, aphids, and moth eggs — the white cocoons riding a hornworm are their calling card, so leave that caterpillar be. Umbel flowers with shallow nectar keep the adults fuelled. Grow to recruit it: Cilantro,Dill,Fennel,Lovage,Parsley,Sweet alyssum
Praying mantisMantidae A sit-and-wait ambusher that snatches caterpillars, beetles, and anything else that wanders close — friend and foe alike, so count it a mixed blessing. Tall, structured plantings give it perches and egg-case anchors. Grow to recruit it: Cosmos,Fennel,Sunflower
Soldier beetleCantharidae Soft-winged beetles seen mating on flower heads in high summer; adults and larvae both take aphids and soft grubs. Open composite flowers are their landing pads and hunting grounds. Grow to recruit it: Echinacea,Rudbeckia,Sunflower,Yarrow,Zinnia
SpidersAraneae Webs, ambushes, and night patrols make spiders the garden’s steadiest generalist predators, taking whatever flies or crawls past. Mulch, ground cover, and undisturbed corners keep the population dense. Grow to recruit it: Lavender,Thyme