Root aphids
Root aphids are aphids that live on roots, where the soil protects them from most controls. They are 2–3 mm long, yellow, green or brown, and usually coated in white wax that builds up on the roots and in the compost. Infested plants wilt, stunt and discolour for no visible reason. They are hard to eliminate. Check the roots of new plants, wash the compost off the roots of a valued plant and repot it into fresh compost, or take cuttings and discard the rest.
Root aphid colony with white wax on a root ball. Photo: pending.
Identification
Root aphids are not one species. The RHS lists lettuce, cabbage, carrot, bean, auricula and rose root aphids; in greenhouses and hydroponic systems the rice root aphid, Rhopalosiphum rufiabdominale, attacks the roots of many plants. They are 2–3 mm long, yellow, green or brown, and usually covered in white wax that builds up on the roots.
They are smaller than mealybugs, and their cornicles, the two tubes at the tail end, are reduced to short rings. Root mealybugs, found in the same pots, have no obvious filaments and also leave wax, so use a hand lens. Springtails in the compost jump when disturbed.
Easily confused with
- Root mealybugsAlso a pestBoth leave white wax on roots. Under a lens, root aphids are smaller than mealybugs and have two ring-like cornicles near the tip of the abdomen.
Damage symptoms
Above ground, everything looks like drought or root rot: wilting, stunting, discoloured leaves and early leaf drop. Lettuce wilts during the day, the heads stay soft, and badly affected roots turn brown and die. The diagnosis is made on the roots: white, powdery wax with aphids among it, building up through the compost.
- Wilting during the day
- Stunted growth and discoloured leaves
- Early leaf drop
- White powdery wax on the roots and through the compost
- Small yellow, green or brown aphids clustered on the roots
Lifecycle & degree days
The details depend on the species. The lettuce root aphid spends the winter as eggs on the bark of Lombardy poplar, where galls form on the leaf stalks. It reproduces once on the poplar, then migrates to lettuce roots, where winged adults later develop and spread it between fields. Under glass and indoors, colonies live on the roots of pot plants, which is why the RHS advises checking the roots of plug plants and new plants. Outdoors, the RHS finds them most active from spring to late summer.
- Size
- 2–3 mm
- Active outdoors
- Spring to late summer
- Winter host
- Lombardy poplar, as eggs (lettuce root aphid)
- Spread
- Winged adults; infested plants and plugs
Host crops
Root aphids feed on a wide range of plants: grasses, weeds, vegetables and Primula (RHS), with lettuce, the cabbage family, carrots, and runner and French beans among the named hosts; the RHS photo shows them on Crassula roots. UConn lists aster, coreopsis, lysimachia, sedum, sempervivum and veronica among greenhouse perennials to scout for them. The rice root aphid attacks the roots of many field and greenhouse plants, including in hydroponic systems, and has been studied on cannabis.
Monitoring & action thresholds
None of the extension sources consulted sets a threshold for root aphids on pot plants. For lettuce, UC advises examining the roots of stunted or wilting plants, and not planting lettuce near Lombardy poplars.
Knock a failing plant out of its pot and look at the outside of the root ball and the inside of the pot for white wax and clustered aphids. Check the roots of plug plants and new purchases before potting them on. In a lettuce field, look for stunted or wilting plants and dig up their roots; nearby Lombardy poplars with galls on the leaf stalks are a warning.
Biological control
There is little tested biological control for root aphids. For lettuce root aphid, UC IPM reports that the fungus Beauveria bassiana (Mycotrol ESO) applied together with azadirachtin gave good control of root aphids in similar crops. Suppliers list the soil predatory mite Stratiolaelaps scimitus and the rove beetle Dalotia coriaria against root aphids, and some sell beneficial nematodes for them, but no trial of these against root aphids was found, and the main Steinernema feltiae product pages (Koppert Entonem, Arbico NemAttack Sf) do not list aphids. Treat any predator or nematode release as an experiment.
Cultural controls
Root aphids are difficult to eliminate once they are established, because life in the soil protects them from many control methods. Most of the work is keeping them out, and cutting losses on plants that are already infested.
- Check the roots of plug plants and new plants before potting them on
- Wash the compost off infested roots and repot valued plants into fresh compost
- Take cuttings of healthy parts of infested plants, and discard the rest
- Water and feed properly, so plants tolerate light infestations
- Outdoors, don't replant a susceptible crop in the same soil for a year, and keep lettuce away from Lombardy poplars
- Grow resistant lettuce varieties where lettuce root aphid is a problem
Chemical, last resort
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
RHS — Root aphids
UC IPM Lettuce Pest Management Guidelines — Lettuce root aphid (updated 2017)
UMass Extension — Aphids on Greenhouse Crops (Smith, upd. Madeiras, 2022)
UConn Extension — Scouting for Key Insect and Mite Pests on Key Greenhouse Plants
UC IPM Pest Notes: Mealybugs, Pub. 74174 (M.L. Flint, 2016)
Acosta, Lee-Rodriguez & Canas, STAR Protocols 6:104222 (2025) — rice root aphid
Ong et al., Archives of Virology (2025) — rice root aphid on cannabis
Koppert — Entonem; Arbico Organics — NemAttack Sf and root aphid pages
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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