How do aphids damage plants

Help us achieve our goals Make a donation. Join the RHS today and support our charity Join now. Save to My scrapbook. Mottled arum aphid on dahlia. Quick facts. Common names Aphids, greenfly, blackfly, plant lice Scientific name Various; many species Plants affected Most plants are susceptible Main symptoms Poor and distorted growth, sticky honeydew and sooty moulds Most active Spring to late summer on garden plants; all year round indoors.

Jump to What are aphids? Symptoms Control Biology. What are aphids? Symptoms You may see the following symptoms: It is usually possible to see aphid colonies with the naked eye, many species colonise shoot tips, flower buds and the underside of younger leaves Aphids can cause stunted growth with curled or distorted leaves and can weaken the plant Many aphids excrete a sticky honeydew on which black sooty moulds can grow White cast skins of aphids can accumulate on the upper surface of leaves Ants may be found climbing plants with aphid colonies, they tend the aphids obtaining honeydew as a reward.

The ants will remove aphid predators. Aphids secrete honeydew on foliage, stems and fruits, which attracts the growth of sooty moulds. Here you can also see white cast aphid skins.

Biology The life cycles of each aphid species differ in general for much of the year, aphid colonies consist of wingless females that give birth to live young. See also You may also like. Aphid predators. Chemical labels explained. Chemicals: storing and disposing safely. Chemicals: using a sprayer. Chemicals: using safely and effectively.

Cherry blackfly. Conifer aphids. Currant blister aphid. Cypress aphid. Fruit aphids. Green spruce aphid. Harlequin ladybird. Hellebore aphid. They're located in a tissue-piercing stylet the insect sinks into stem, leaf or root tissue. For about one minute after it hits a phloem-transporting vessel, the insect pumps watery, sap-diluting saliva into the plant. It then starts sucking the saliva-and-sap mixture back up through the food canal while continuing to pump saliva into the feeding site.

The saliva prevents defensive chemicals in the plant from clotting the damaged cells and stopping the sap flow. Most plants tolerate light aphid feeding with no discernible damage. As the aphid population grows, however, infested leaves start wilting and yellowing from nutrient loss. Aphid feeding often stunts newly emerging growth. In large numbers, root aphids may drain enough sap that a plant stops growing.

Some species, such as the leafcurl ash aphid Prociphilus fraxinifolii and plum leafcurl or leafcurl plum aphid Brachycaudus helichrysi , inject their hosts with cell-distorting saliva that permanently curls the young leaves they feed on, and the curls are protective shelters for the aphids.

Aphids damage plants most seriously by transmitting numerous viruses. Aphids on an overcrowded hosts begin producing winged offspring that leave for less congested quarters. When in flight, the insects can't identify their host plants. Because each adult aphid can produce up to 80 offspring in a matter of a week, aphid populations can increase with great speed.

Low to moderate numbers of leaf-feeding aphids aren't usually damaging in gardens or on trees. However, large populations can turn leaves yellow and stunt shoots ; aphids can also produce large quantities of a sticky exudate known as honeydew, which often turns black with the growth of a sooty mold fungus. Some aphid species inject a toxin into plants, which causes leaves to curl and further distorts growth.

A few species cause gall formations. Aphids may transmit viruses from plant to plant on certain vegetable and ornamental plants. Squash, cucumber, pumpkin, melon, bean, potato, lettuce, beet, chard, and bok choy are crops that often have aphid-transmitted viruses associated with them. The viruses mottle, yellow, or curl leaves and stunt plant growth. Although losses can be great, they are difficult to prevent by controlling aphids, because infection occurs even when aphid numbers are very low; it takes only a few minutes for the aphid to transmit the virus, while it takes a much longer time to kill the aphid with an insecticide.

A few aphid species attack parts of plants other than leaves and shoots. The lettuce root aphid is a soil dweller that attacks lettuce roots in spring and summer, causing lettuce plants to wilt and occasionally die. In fall, this species often moves to poplar trees, where it overwinters in the egg stage and produces leaf galls in spring.

The woolly apple aphid infests woody parts of apple roots and limbs, often near pruning wounds, and can cause overall tree decline if roots are infested for several years. Heavy infestations of crown and root aphids on carrots may weaken tops, causing them to tear off when carrots are harvested. Although aphids seldom kill a mature plant, the damage they do and unsightly honeydew they generate sometimes warrant control. Consider the nonchemical controls discussed below, as most insecticides will destroy beneficial insects along with the pest.

On mature trees, such as in citrus orchards, aphids and the honeydew they produce can provide a valuable food source for beneficial insects. Check your plants regularly for aphids—at least twice a week when plants are growing rapidly—in order to catch infestations early, so you can knock or hose them off or prune them out. For aphids that cause leaves to curl, once aphid numbers are high and they have begun to distort leaves, it's often difficult to control these pests, because the curled leaves shelter aphids from insecticides and natural enemies.

Aphids tend to be most prevalent along the upwind edge of the garden and close to other infested plants of the same species, so make a special effort to check these areas. Many aphid species prefer the underside of leaves, so turn leaves over when checking for aphids.

On trees, clip off leaves from several areas of the tree. Also check for evidence of natural enemies such as lady beetles, lacewings, syrphid fly larvae, and the mummified skins of parasitized aphids. Look for disease-killed aphids as well; they may appear off color, bloated, flattened, or fuzzy.

Substantial numbers of any of these natural control factors can mean the aphid population may be reduced rapidly without the need for treatment. Ants are often associated with aphid populations, especially on trees and shrubs, and frequently are a clue that an aphid infestation is present. If you see large numbers of ants climbing your tree trunks, check higher up the tree for aphids or other honeydew-producing insects that might be on limbs and leaves. To protect their food source, ants ward off many predators and parasites of aphids.

Managing ants is a key component of aphid management. See Cultural Control. In landscape settings, you can monitor aphids by using water-sensitive paper to measure honeydew dripping from a tree. This type of monitoring is of particular interest where there is a low tolerance for dripping honeydew, such as in groups of trees along city streets or in parks and for tall trees where aphid colonies may be located too high to detect.

Natural enemies can be very important for controlling aphids, especially in gardens not sprayed with broad-spectrum pesticides e. Usually natural enemy populations don't appear in significant numbers until aphids begin to be numerous. Among the most important natural enemies are various species of parasitic wasps that lay their eggs inside aphids. The skin of the parasitized aphid turns crusty and golden brown, a form called a mummy.

The generation time of most parasites is quite short when the weather is warm, so once you begin to see mummies on your plants, the aphid population is likely to be reduced substantially within a week or two.

Many predators also feed on aphids. The most well known are lady beetle adults and larvae, lacewing larvae, soldier beetles , and syrphid fly larvae. Naturally occurring predators work best, especially in garden and landscape situations.

For photos and more information about aphid natural enemies, see the Natural Enemies Gallery. Applying commercially available lady beetles the convergent lady beetle , Hippodamia convergens may give some temporary control when properly handled, although most of them will disperse from your yard within a few days.

If releasing lady beetles, keep them refrigerated until just before letting them go, doing so at dusk, as those released in broad daylight will fly away immediately. Mist the lady beetles with water just before release, and also mist the surface of the plant you are releasing them onto. Place the lady beetles at the base of infested plants or in the crotches of low branches.

Lady beetles will crawl higher into the plant in search of aphids. University of California research indicates that high numbers of lady beetles are required to control aphids.

One large, heavily infested rose bush required two applications, spaced a week apart, of about 1, lady beetles each. Aphids are very susceptible to fungal diseases when it is humid. These pathogens can kill entire colonies of aphids when conditions are right.

Look for dead aphids that have turned reddish or brown; they'll have a fuzzy, shriveled texture unlike the shiny, bloated, tan-colored mummies that form when aphids are parasitized.

Weather can also impact aphids. Summer heat in the Central Valley and desert areas reduces the populations of many species, and aphid activity is also limited during the coldest part of the year. However, some aphids may be active year-round, especially in the milder, central coastal areas of California. In some situations ants tend aphids and feed on the honeydew aphids excrete.