cotton aphid

Symptoms

Yellow-green aphids clustering on shoot tips.

Plants affected

• dahlia
• florist's chrysanthemum
• pistachio
• melon
• fuchsia
• pansy
• okra (lady's finger)
• watermelon
• lily
• red currant
• eggplant
• tulip

Easily confused with

• two-spotted spider mite

  How to tell them apart: Aphis gossypii (cotton/melon aphid): look for visible soft-bodied, pear-shaped insects 1-2 mm long, clustered densely on shoot tips, flower buds and the youngest leaf undersides; colour ranges from yellow-green to dark mottled green or near-black. They leave sticky shiny honeydew that turns into black sooty mould, and you can often see cast white skins and a pair of small tube-like cornicles at the rear of the body. Tetranychus urticae (two-spotted spider mite): you will NOT see obvious insects — look instead for extremely fine, dust-like specks (0.5 mm) that need a hand lens, each pale green-yellow with two dark spots, scattered on the leaf underside. Its signature is the dense pale stippling/bronzing of the upper leaf surface and very fine silken webbing strung between leaf edges and shoot tips, worst in hot dry conditions; there is no honeydew and no sooty mould.

• silverleaf whitefly

  How to tell them apart: Aphis gossypii (cotton/melon aphid): look on stems, growing tips and the underside of leaves for dense, slow-moving colonies of soft, pear-shaped, wingless insects, usually pale yellow to dark blue-green with two small tube-like 'tailpipes' (cornicles) at the rear. They stay put when disturbed, leave white cast skins, and curl leaves downward; ants often patrol the colony. Bemisia tabaci (silverleaf whitefly): look for tiny, 1-2 mm snow-white moth-like insects with wings held roof-like over the body, plus scale-like flat oval nymphs and yellow eggs on the leaf underside. The unmistakable sign is a sudden cloud of white flies that flutters up when you shake the plant, something aphids never do, often with silvering or irregular ripening of melon fruit.

• fuchsia gall mite

  How to tell them apart: Aculops fuchsiae (fuchsia gall mite) produces no visible insects — only the damage shows: shoot tips and the youngest leaves swell, thicken and crumple into a coppery-pink to reddish, blistered, witch's-broom mass that hardens and stays distorted even as it matures, so the plant simply stops making normal leaves and flowers. Aphis gossypii (cotton/melon aphid) leaves you the actual insects: dense clusters of small soft-bodied, pear-shaped aphids (yellow-green to dark green) on the underside of curled tips, with shed white skins, sticky honeydew and black sooty mould. Aphid curl is soft, green and reversible once the colony is removed; mite distortion is hard, thickened, abnormally coloured and permanent. Look closely for live aphids and honeydew before assuming gall mite.

• Cucumber mosaic virus (CMV)

  How to tell them apart: Aphis gossypii (cotton/melon aphid): look for the insects themselves — small (1-2 mm) soft-bodied, pear-shaped, yellow-green to dark green aphids clustered on the undersides of young leaves and growing tips. They leave sticky honeydew and black sooty mould on lower leaves, plus shed white skins. Damage is localized to where colonies feed: leaves curl downward and pucker, with diffuse yellowing, and ants often attend the colonies. Cucumber mosaic virus (CMV): there is NO insect and no honeydew — instead the whole plant shows a systemic light-and-dark green mosaic and mottling spread evenly across many leaves, with puckering, fern-leaf narrowing of new growth, marked stunting, and often distorted, warty or mottled fruit. CMV symptoms persist and worsen after any aphids are gone, whereas aphid distortion eases once colonies are removed.

• alkaline-soil chlorosis

  How to tell them apart: Alkaline-soil chlorosis is an abiotic nutrient disorder: leaves yellow BETWEEN the veins while the fine vein network itself stays distinctly green (interveinal chlorosis), worst on the youngest shoot-tip leaves, and there are no insects, no sticky residue and no curling beyond mild cupping. Aphis gossypii (cotton aphid) is a living pest: look on the undersides of young leaves and on soft shoot tips for clusters of soft, pear-shaped yellow-green to dark-green aphids 1-2 mm long, often with white cast skins, and the leaves turn a more uniform pale yellow and curl or pucker. The decisive tell is the aphid's honeydew - a sticky, shiny film on lower leaves often blackened by sooty mould and visited by ants; chlorosis leaves are dry and clean. Chlorosis spreads evenly across many plants on the same alkaline (high-lime) bed and improves with iron/manganese feeding, whereas aphid yellowing is patchy around the colonies.

• iron-deficiency chlorosis

  How to tell them apart: Iron-deficiency chlorosis (abiotic_chlorosis_iron) turns the youngest hibiscus leaves uniformly pale yellow while the veins stay distinctly green — a clean interveinal net — with no insects, no stickiness and no leaf distortion, and it is symmetric across the whole new flush, worsening on alkaline or waterlogged soil. Cotton aphid (Aphis gossypii) instead shows soft yellow-green to dark sucking insects in colonies on shoot tips and leaf undersides, with sticky honeydew, black sooty mould and patrolling ants; the yellowing is blotchy and the new leaves are curled, cupped or stunted rather than evenly greenscreened. Turn a yellow shoot over: bare undersides with a crisp green-vein pattern point to iron; clustered aphids and gloss point to Aphis gossypii.

Common questions

How do I recognise cotton aphid on dahlia?

Yellow-green aphids clustering on shoot tips.

Do I have to report cotton aphid?

No. cotton aphid is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is cotton aphid treated?

Mainly with biological and cultural measures — removing affected material, changing the conditions that favour it, and treating with agents approved in your country. The exact steps and their timing depend on the plant, the season and where you live: Dr. Phyto works them out in a free diagnosis.