CORVALLIS, Ore. — As spring warms up, gardeners should watch for aphids — tiny, soft-bodied insects that thrive on new plant growth and can quickly multiply.
“Because there are so many kinds of aphids with varying life cycles, the best approach is to combine several strategies."
Aphids are pear-shaped insects, about one-tenth of an inch long, with soft bodies that may be winged or wingless. They come in many colors — green, yellow, red (pink), black or brown — and some species are coated with a soft, cottony layer. Their slender, needle-like mouthparts pierce plant tissues to draw out sap.
Most aphids secrete a sticky substance called honeydew, which attracts ants, bees and flies. The dripping honeydew also encourages the growth of sooty mold on plants. In addition, some aphid species can transmit plant viruses from one host to another.
Prevention starts with good garden design
Heather Stoven, horticulturist with the Oregon State University Extension Service, recommends minimizing aphid damage through smart garden planning and care.
“Because there are so many kinds of aphids with varying life cycles, the best approach is to combine several strategies,” Stoven said.
- Use thoughtful landscape design. Avoid planting aphid-attracting species where the insects or their honeydew will cause problems. For example, linden trees draw aphids and can coat decks or vehicles with sticky residue if planted nearby.
- Keep plants healthy. Strong plants resist aphid attacks better than stressed ones. Provide adequate light, water and nutrients, but don’t overfertilize. Excess fertilizer encourages soft, succulent growth that attracts aphids. Slow-release or organic fertilizers help prevent overfeeding.
Simple, nonchemical control methods
- Wash them off. A strong spray of water can remove aphids from rose buds, bean plants, and tender shoots of broccoli, cabbage and other vegetables. Repeat as needed. Prune away badly infested leaves or stems.
- Trap flying aphids. Yellow sticky traps, available at garden stores, capture flying aphids without chemicals. Isolate houseplants if they show signs of infestation.
- Encourage natural predators. Avoid broad-spectrum pesticides that kill beneficial insects such as ladybugs and green lacewings. Don’t release adult ladybugs, as they usually fly away; green lacewings, sold as eggs or larvae, are a better choice.
To attract and support beneficial insects, grow plants such as yarrow, buckwheat, white sweet clover, cosmos, sweet alyssum, spearmint, Queen Anne’s lace, hairy vetch, crimson clover, goldenrod, sunflowers and caraway.
When natural control isn’t enough
If aphid populations persist, Stoven recommends using commercial insecticidal soaps, which are among the least toxic chemical options. These soaps work by direct contact and lose their toxicity once dry, making them safer for pollinators and other beneficial insects.
“Encouraging the survival of beneficial insects such as ladybugs provides ongoing natural pest control,” Stoven said. “Commercial formulations of insecticidal soap have been tested on plants and are safer than homemade versions.”
Learn more
Find additional information about identification and management of aphids in the PNW Pest Management Handbooks.
Previously titled How to control aphids with less toxic methods
