One of the unwanted visitors to the spring garden arrives just about now. That pulsating mass of tiny pests that cloak the new growth on your roses, viburnums, or peach trees are at best an unsightly nuisance and at worst, creatures that can damage tender new growth on plants and spread disease. Welcome to the world of aphids.
The aphid family contains over 200 species of insects that suck the juices out of a wide variety of landscape plants and agricultural crops. Almost every plant has one or more aphid species that occasionally feeds on it. The small pear-shaped, soft-bodied insects are most often green in color, but can be white, yellow, pink, brown, black, or mottled. Some even look waxy or woolly from a secretion they exude over their body surface. In addition to long legs and antennae, they have black cornicles (“exhaust pipe” tube-like projections at the rear of the abdomen) that distinguish them from all other insects.
While you may observe an aphid feeding singly, most often they’re seen in masses, covering succulent new growth on plants. Their long, slender mouth parts pierce stems, leaves, and other tender plant parts and suck up plant liquids. Really large colonies of feeding aphids can weaken plant growth, cause leaves to yellow, curl or drop early. Some species can distort plant stems or fruit or cause galls on stems, leaves, or roots. As they feed, they produce honeydew that attract ants. In fact, many species of ants are so addicted to this sweet drink that they will protect the aphids from various predators and move them to new plants if the one they are on starts to wilt. Some ants even build small shelters over species that feed near the base of the plant, to keep root-aphids inside their own nests. Any honeydew the ants don’t consume can end up supporting the growth of black sooty mold.
The best method of control is prevention. Aphids love the rapidly growing new growth on plants receiving high levels of nitrogen fertilizer, so don’t use any more nitrogen than needed. If you see them, knock them to the ground with a strong stream of water. They’re poor climbers and probably won’t re-establish; they also run a high risk of getting eaten by ground-roving insect predators.
They’re the favored food of many natural enemies including lady beetles, soldier beetles, lacewings, and syrphid fly larvae. Encouraging these beneficials into your garden can often keep aphid populations in check. If natural predators or a blast of water isn’t enough to control these pesky creatures, try using an insecticidal soap.