Aphids are small, soft-bodied insects that colonize and feed on many types of garden plants, causing damage to leaves and shoots and spreading disease. As garden pests go, they can be difficult to spot, but not all that difficult to control.
Here’s what you need to know to deal with aphids in your garden.
Aphids thrive in warm weather, and in mild climates they can be active all year long. Although they may just look like tiny specks on your plants, aphids are actually small, soft-bodied insects that pierce the stems and leaves of plants to draw out juices. This not only causes damage to the shoots, but can also transmit viruses and diseases from other plants.
After feeding, aphids excrete a sugary substance called honeydew, which coats the plant and quickly invites the growth of mold and fungus.
How to Identify Aphids
Aphids are small, slow-moving insects that may resemble specks of dirt. To spot an aphid infestation on plants, look for:
Aphid Colonies: Aphids can be red, green, brown, yellow, or black in color. They often colonize near the tender tips of shoots, where the plants are the softest and juiciest. Aphids can also be found on the undersides of leaves, and a few species attack plant roots as well.
Ants: Ants love to eat aphid honeydew, and they will actually protect and herd aphids like livestock. Often you can find an aphid infestation by spotting ants scurrying up and down the stems.
Predators: A number of insects like to eat aphids and can signal their presence, including lacewings and ladybugs. Parasitic wasps will lay eggs inside of aphids, turning their bodies into a crusty “mummy” that will be visible on the plant.
Plant Damage: Aphid damage often causes a distortion, curling, or yellowing of young shoots. The honeydew quickly turns black with fungal mold growth.
How To Control Aphids
A few aphids generally don’t cause much of a problem, but if the colony grows, it can begin to damage plants. Aphids are easy to control using organic means, and chemical pesticides aren’t necessary unless the infestation is severe.
Here are some tips for getting rid of aphids:
Garden Hose: For small numbers of aphids, simply knock them (and the ants) off your plant with a spray of water from the hose. They often won’t return, and the water will rinse away the honeydew as well. You can do this when watering, for easy control of mild infestations.
Insecticidal Soap: A mild spray of insecticidal soap works wonders on aphids, killing them pretty much instantly. You have to spray aphids directly, and you need to spray both the tops and bottoms of the leaves; but the results are instant, thorough, and nontoxic to the environment, beneficial predators, and pollinators. This is my favorite way to control aphids; and for most infestations, you can maintain control with weekly monitoring and a few spritzes of insecticidal soap when needed.
Control Ants: Ants protect aphids from natural predators, so discouraging ants can help control aphids naturally. Woody plants and trees can be protected by a sticky ant barrier (such as Tanglefoot) around the trunk, or you can use baits or traps for ants on the ground.
Remove Damage: If aphids are eating the tips of shoots, prune them away before the damage is too severe. Not only will pruning remove most of the colony, but you’ll also remove the damaged, curled leaves than can protect aphids from spray treatments.
Oils: Horticultural oils and neem oil are also effective against aphids. Like insecticidal soaps, they need to be sprayed directly on infested foliage and require thorough coverage. Don’t use oils or soaps when temperatures are above 90° F, since they can burn plants. Dormant oils, applied in late winter, can kill aphid eggs on trees but aren’t recommended as a primary control unless they’re being used for other reasons.
Pesticides: A number of pesticides are effective against aphids, including natural pyrethrum and synthetic products. Check the labels to be sure the product is rated for control of aphids. Use pesticides with caution, since they kill beneficial insects and can be toxic to humans and pets.
Natural Predators: You can also encourage – and even purchase and release – natural predators for control of aphids and other garden pests. Lacewings, ladybugs, and syrphid flies are the most common predators of aphids. In a home landscape, the best way to encourage natural predation is by avoiding broad-spectrum chemical pesticides and encouraging a more natural ecosystem.
Organic Fertilizer: Since aphids prefer tender shoots, they can be attracted to the lush, soft growth caused by overuse of nitrogen fertilizers. Instead, use slow-release organic fertilizers or compost that promote more steady growth.