Symptoms

One or two aphids on a leaf do not cause any serious harm to any plant. However, they multiply so fast, in a matter of days, that those two can become hundreds and are too numerous to be ignored. As they suck the sap from cells of plant leaves, fruits, flowers, stems, and--with some aphid species--the roots as well, they inject saliva into a plant. This causes foliage of heavily infested plants to curl, pucker, and turn yellow, and their vigor declines. In some cases aphids carry viral diseases which they introduce into infested plants. In addition, the honeydew aphids excrete promotes the growth of black sooty mold which coats plant surfaces, signaling their presence.

Aphids threaten young plants most. They can severely damage seedlings and young trees. New growth is stunted. Check the undersides of leaves, especially the new leaves, for small groups of aphids. They also cluster on the tender new buds and stems. On trees and shrubs, you may find cottony masses on trunks and twigs. Under all the cottony fuzz you’ll find aphids. The woolly aphid is the most common example of this type of aphid.

Underground Aphids

Certain aphids, such as the corn root aphid, live in the soil and attack roots and other underground plant parts such as bulbs. If you suspect an attack by soil-dwelling aphids, examine the roots of your plants for knotted growths caused by the aphids. As they do for aboveground aphid species, ants often bring these soil-dwelling aphids to your plants. They will carry young aphids through their tunnels to plant roots to allow them to feed, and will nurse aphids’ eggs through the winter. Besides the knotted roots, plants infested with root aphids show the same symptoms as those attacked by above-ground aphids--distorted, yellowed foliage.

Plants Attacked By Underground Aphids
Aster	Beets	Browallia	Calendula
Carrots	Corn	Cosmos	Crocus
Dahlia	Freesia	Gladiolus	Iris
Lily	Primrose	Roses	Siberian
Squill
Sunflower	Sweet pea	Tulip	Vinca