Black Aphids on Plants: Are They Harmful?

Black aphids are small sap-sucking insects that rarely kill an established plant, but a big colony can stunt shoots, curl leaves and spread plant viruses. On a healthy plant a few are usually harmless, according to UC IPM, and NC State Extension notes that large black conifer aphids (Cinara) are harmless to people and do not bite. This guide shows how to tell which black aphid you have, when to act, what spray trials measured, and how much a soap spray costs for your own plants.

Are black aphids harmful to plants or people?

Aphids feed on plant sap with piercing mouthparts. NC State Extension notes that large black conifer aphids (Cinara) are harmless to people and do not bite. The sticky honeydew they leave behind wipes off with a damp cloth, as the Royal Horticultural Society notes.

For plants, it depends on the plant and the numbers. UC IPM says most established plants tolerate aphid feeding and outgrow the damage. The RHS says aphids kill plants very rarely and that you do not have to control them. Young shoots, seedlings and crops sold fresh are different. Large colonies can turn leaves yellow, stunt shoots and coat leaves with honeydew, and some aphids carry viruses.

• Direct damage: sap loss, curled and distorted leaves, weak new growth. On broad beans, pod set can be poor when plants are heavily affected (RHS).
• Honeydew and sooty mould: the black film that grows on honeydew does not infect the plant, says UC IPM, but it covers leaves and can lower their quality.
• Viruses: UC IPM lists squash, cucumber, bean, potato, lettuce and beet among crops that often have aphid-borne viruses. Infection can happen at very low aphid numbers, so spraying does not always stop it.
• Contaminated produce: in celery, UC IPM notes that honeydew and debris can lower the value of fresh-market crops.

What black aphids look like and which species they are

“Black aphid” is a common name, not one species. UC IPM describes aphids as soft, pear-shaped insects with long legs and antennae, and says the colour can be green, yellow, brown, red or black depending on species and host. Most have two tube-like cornicles at the rear, which separate aphids from other insects.

The one most gardeners and bean growers meet is the black bean aphid, Aphis fabae. The RHS blackfly page says it is up to 2 mm long, mainly black, sometimes with white flecks, and forms dense colonies on soft shoot tips, flower stems and the underside of young leaves. Typical hosts include broad, French and runner beans, nasturtium and dahlia. Ants often tend the colony and drive off ladybird larvae.

For a close look at one crop, our page on the black citrus aphid covers orchard trees.

▶ A long guide to aphid biology, damage and control, indoors and outdoors. · 28:21

Why some black aphids have wings

Winged black aphids are normal. They are the stage that moves to a new plant. UC IPM says most species have winged forms, especially when numbers are high or in spring and fall. UC IPM’s celery guide adds that overcrowding and plant stress trigger winged bean aphids.

The black bean aphid’s year, per the RHS, has two halves. Eggs overwinter on shrubs such as spindle, viburnum and philadelphus. Wingless females breed on the new spring leaves. By May the leaves toughen and days lengthen, and a winged generation flies to summer hosts such as beans. In late summer another winged generation flies back to the shrubs, mates and lays eggs. Black aphids that turn up indoors are often winged ones that flew in or arrived on a new plant. See our guide to winged aphids for more.

How fast black aphids multiply

Speed is why a small group becomes a problem. In warm weather UC IPM says many aphids grow from newborn to reproducing adult in seven to eight days, and one adult can produce up to 80 young in a week. In a lab study of Aphis fabae on faba bean at four constant temperatures (15, 20, 25 and 30 °C), the highest growth rate, 0.4347 per day, came at 25 °C (Akca et al., 2015).

The chart turns that growth rate into a simple projection. Real colonies grow far less than this, because predators, parasitic wasps, weather and plant quality hold them back. UC IPM’s celery guide notes that in the field bean aphids can reach several thousand per plant, but that in some cases parasitic wasps can clear dense colonies in a few weeks.

Chart

Unchecked growth of one black bean aphid

Total aphids if numbers grow at the lab rate of 0.4347 per day (25 °C), with no predators or crowding

When black aphids need treatment

Start with how much damage you can accept. The RHS advises tolerating aphids where possible and checking plants often so you can act before damage develops. UC IPM says low to moderate numbers on leaves are not usually damaging in gardens. In commercial crops, thresholds depend on the crop. UC IPM says no treatment threshold has been set for aphids on celery, and that young celery can tolerate them, while fresh-market stalks matter most once petioles form.

Act sooner when:

• shoot tips are curling and the colony is spreading to new growth;
• you grow a crop that is sold fresh, or one with known aphid-borne viruses;
• ants are farming the colony and predators are absent.

How to get rid of black aphids on plants

1. Check for ants first. UC IPM and the RHS both say ants protect aphids from natural enemies. Keeping ants off plants lets predators work.
2. Squash or prune. The RHS suggests squashing colonies with finger and thumb and pinching out badly hit shoot tips. UC IPM suggests pruning infested leaves and stems.
3. Hose them off. UC IPM recommends a strong stream of water on sturdy plants. Colorado State University Extension says this is most effective on aphids and spider mites.
4. Use soap or oil only if needed. UC IPM says soaps and oils work by smothering, so coverage must be thorough, and they should not be applied to drought-stressed plants or in very hot weather. Aphids inside curled leaves are not reached, so prune those out.
5. Wait for the predators. The RHS notes that aphid numbers rise in spring before natural enemies are active in numbers, and that waiting often lets them do the work.

Always follow the product label and your local rules when using any spray. The RHS does not support pesticide use for aphids in gardens, because even organic products can harm natural enemies.

▶ Strategies for sustainable aphid control on farms. · 12:44

What spray trials show

Trial data on black bean aphid itself is thin, so the two charts below use the best published aphid spray trials we could open. Both come from University of Maryland field and greenhouse work on other aphids (Dively et al., 2020), so treat them as a guide to how products behave, not a promise for black aphids.

Chart

Percent control by product and aphid

Mean % control versus untreated plots, University of Maryland trials; green peach aphid on cabbage and collards (weekly sprays) versus pea aphid on alfalfa (one spray)

Across 12 aphid trials, the products reduced green peach aphid on cabbage and collards by 52.6% to 78.3% on average with weekly sprays, but a single spray cut pea aphid on alfalfa by only 16% to 20%. The authors report no significant difference between the three products on green peach aphid. In a greenhouse trial on pansies, a mineral oil, a soap, a neem-extract product and an adjuvant gave 28% to 62.5% control against a heavy infestation.

The lesson is practical. Repeat sprays matter, results differ by aphid and crop, and a spray that hits the insects directly works better than one that does not.

Chart

Greenhouse trial on heavy green peach aphid

% control versus untreated pansies, 2008 trial; sprays at 2% v/v, Oroboost at 4%

Neem oil, soap and other sprays: what to check

Neem oil is a common choice for garden aphids. The National Pesticide Information Center says neem oil is practically non-toxic to birds, mammals, bees and plants, and that insects must eat the treated plant to be killed, so pollinators are unlikely to be harmed. It is slightly toxic to fish. In the Maryland trials, the azadirachtin product Neemix had the lowest average control of the three on green peach aphid (52.6%). Read more about neem in our guide to neem oil.

For insecticidal soaps, Colorado State University Extension gives a dilute spray strength of one to three percent for houseplants. Many liquid hand soaps and dish detergents also kill insects, but they can burn plants, so test a small area first and follow label directions on any product you buy.

Systemic neonicotinoids are different. UC IPM says that as of January 2025 systemic insecticides are only available to licensed pest control professionals in California, because they are more toxic and can harm bees and beneficial insects. In the European Union, all outdoor uses of imidacloprid, clothianidin and thiamethoxam were banned by regulations published on 30 May 2018, and only permanent greenhouse use remained (European Commission). Rules vary by country and state, so check yours.

Try the numbers for your own farm below.

Black aphids on indoor plants

Indoors there are few predators, so isolate the plant first. Colorado State University Extension says washing with a vigorous jet of water, or dunking a plant in water for one to two hours, can control insects on the upper plant. It also says yellow sticky traps catch winged aphids but will not solve the problem alone, since much of the population stays on the plant. For houseplants it notes that aphid generations can finish in two to three weeks and that insecticidal soap and horticultural oil are common options. Seriously infested plants are sometimes best thrown away, and new plants are worth checking before you place them near others.

Natural predators of black aphids

UC IPM lists lady beetles, lacewings, syrphid fly larvae, soldier beetles and tiny parasitic wasps. The larvae of these insects do most of the aphid eating, and the wasps leave tan, round “mummies” on leaves, which you should leave in place. To help them, avoid broad-spectrum insecticides and plant flowers that offer nectar and pollen. For ideas, see our page on black aphid predators.

Preventing black aphid problems

• Do not over-fertilise. UC IPM says aphids feed on soft new growth, and recommends slow-release products.
• Protect seedlings. UC IPM suggests covers or aluminium foil mulches.
• Remove nearby host plants. For celery, UC IPM says removing weeds and woody shrubs that host aphids can reduce field infestations, and crop residue should be destroyed after harvest.
• Check often. Look at shoot tips and leaf undersides weekly in spring.

Which aphids feed on which plants

Black aphids are only some of the aphids you may meet. UC IPM’s list of common aphids on vegetables and flowers shows how much the hosts overlap, which is why a plant in your garden can carry several kinds in one season.

UC IPM adds that many aphid species are hard to tell apart, but that management of most of them is similar. So the steps in this guide work for the whole group, even when you cannot name the species.

Black aphids by plant: what to watch

The damage you see depends on the host. The notes below come from the RHS and UC IPM and cover the plants people ask about most.

• Beans and other legumes: the black bean aphid is active from April to August in Britain (RHS). Plants may grow less well and set fewer pods, but the beans inside are undamaged and edible.
• Flowers such as dahlia, nasturtium and poppy: feeding on developing flowers can damage flower formation (RHS).
• Winter host shrubs: spindle, viburnum and philadelphus often show curled leaves in response to feeding, but the RHS calls the damage minor and says the plants usually recover.
• Cherry trees: a different species, cherry blackfly, distorts foliage, but the RHS says this does not stop trees flowering or bearing fruit.
• Conifers: the RHS says honeydew and sooty mould often reveal conifer aphids, and that they can cause shoot dieback.
• Celery: UC IPM says bean aphid feeding can distort growth more than other aphids and can carry celery mosaic, calico and yellow spot viruses. It tolerates heat better than other aphids, so it can be a problem in summer too.

A simple year of black aphid scouting

The life cycle gives you a rough calendar. It follows the black bean aphid in a temperate climate, using the RHS description, so shift the dates for your own region.

• Early spring: eggs hatch on winter host shrubs as new leaves open. Check shoot tips on spindle, viburnum and philadelphus.
• Late spring: a winged generation leaves the shrubs. Look at the tips of young beans and flowers, because colonies start here. Predators are often still few at this point.
• Summer: wingless colonies build on summer hosts. UC IPM notes that some aphids are heat-intolerant and disappear by mid-summer, while bean aphid is more heat-tolerant.
• Late summer and fall: winged aphids fly back to the shrubs, mate and lay eggs around buds and in crevices on stems.

Ants and black aphids

Ants are easy to overlook. They collect the honeydew and, according to the RHS, remove aphid predators such as ladybird larvae. UC IPM says keeping ants off plants lets beneficial insects do their job. In practice, if you see a steady line of ants up a stem, deal with the ants as well as the aphids, otherwise the colony may return even after you hose it off.

Watching large plantings

On a large farm you cannot walk every row each week. Satellite images show where vegetation looks different from the rest of a field, which tells you where to scout first. They do not show the pest or its cause, so check those spots on foot. Farmonaut Satellite + AI Farm Monitoring System gives field maps through the application page, and developers can use the API documentation or the Farmonaut Satellite & Weather API Developer Docs.

▶ Scouting and control strategies for soybean aphid, showing why early detection matters. · 22:28

FAQ

Are black aphids harmful to humans?

Aphids feed on plant sap. NC State Extension notes that large black conifer aphids (Cinara) are harmless to people and do not bite. Honeydew on leaves can be wiped off with a damp cloth (RHS).

Are black aphids bad for plants?

Sometimes. Most established plants tolerate them (UC IPM), but heavy colonies can stunt young shoots and spread viruses.

Can black aphids fly?

Yes, some can. Winged forms appear when colonies are crowded or plants are stressed, and in spring and fall (UC IPM).

Where do black aphids come from?

Black bean aphids overwinter as eggs on shrubs like spindle and viburnum, then fly to summer hosts such as beans (RHS).

How do I get rid of black aphids on plants?

Check for ants, squash or prune colonies, hose them off, and use soap or oil with thorough coverage only if needed. Follow the product label.

Do black aphids survive winter?

The black bean aphid overwinters as eggs on shrubs; other species can stay active in mild winters or indoors (RHS).

Does neem oil work on black aphids?

It can reduce them, but results vary. In the Maryland trials a neem-based product (azadirachtin) averaged 52.6% control of green peach aphid with weekly sprays. NPIC notes insects must eat the treated plant to be affected. Follow the label.

How long until black aphids go away?

A strong water jet or a soap spray works on the insects it touches, so repeat if needed (UC IPM says applications may need to be repeated). In some cases parasitic wasps can clear dense colonies in a few weeks (UC IPM, celery).

Related pages on our site: pest thresholds and integrated pest management, aphids compared with mealybugs, agricultural cooperation.