Aphids are tiny. They barely move. They don’t sting or bite. You can squish them with a fingertip. So why are they so creepy? Maybe it’s because these soft-bodied, sap-sucking insects tend to appear in clusters. When you notice a leaf has curled oddly and you turn it over to see what’s going on, you don’t find just one tiny aphid—instead you find a whole brigade. Yuck. Aphids come in lots of colors, from pale green to bright red, so some are easier to find than others.
Damage
Aphids feed by piercing leaves and stems and sucking out a plant’s juices. Infested plants have curled or puckered leaves, yellow or brown discoloration, or stunted or distorted blossoms. Another common problem is black sooty mold, which grows on the aphids’ sugary liquid waste (called honeydew). Ants are often attracted to honeydew deposits. Aphids can also carry viruses from plant to plant.
Control
The garden hose is your first defense against an aphid infestation. Simply direct a strong jet of water at the infested plant, especially underneath leaves. Do this every morning for at least three mornings in a row. The wingless aphids knocked off plants are generally not able to climb back up. Aphids are food for some beneficial insects, including ladybugs, green lacewings, and braconid or chalcid wasps, so try releasing some of these natural predators in your yard. In fall, clean up leaves and twigs to prevent aphid eggs from overwintering in your flower beds.
For aphids, spring is the most delicious time of year—their favorite food is the fresh new leaves that emerge during this season. If you notice curled and crinkled leaves, a sticky goo and black mold on plants, and tiny creatures with two short tubes (cornicles) extending from the end of their bodies, it means aphids are using your garden as their own personal buffet. Here are five tips for controlling aphids:
1. Train a strong stream of water on affected leaves. Be sure the water hits the undersides of leaves, where aphids usually hide.
2. Remove damaged leaves.
3. Since aphids are attracted to new plant growth, don’t use a high-nitrogen fertilizer that stimulates a quick flush of new leaves. Instead, use slow-release or organic fertilizers, which release nutrients over time.
4. Purchase eggs or larvae of green lacewings (which feed on aphids) and sprinkle them on aphid-infested plants, or grow plants that attract aphid predators. These include yarrow, wild buckwheat, sweet alyssum, Queen Anne’s lace, and crimson clover.
5. Don’t use broad-spectrum pesticides; these kill beneficial aphid predators such as ladybugs, parasitic wasps, and green lacewings. If you need to use a pesticide, try commercial insecticidal soaps, which kill soft-bodied aphids but don’t affect their hard-bodied predators.
—Photo courtesy of the Kemper Center for Home Gardening at the Missouri Botanical Garden.