How to Kill Aphids on Orchids

Every continent but Antarctica has its share of more than 30,000 orchid species, tolerating temperatures from the bone-chilling winters of U.S Department of Agriculture plant hardiness zone 2 to the scorching summers of USDA zone 12. On every one of those continents, tiny insects called aphids seek out orchids with the passion of orchid hunters in search of ever-more-exotic discoveries. To paraphrase Shakespeare's Hamlet, "When aphids come, they come not as single pests but in battalions." Kill them with a biological or chemical counterattack, but also take precautions to protect yourself.

The ultimate in-your-face plant pests, aphids have no qualms about letting their presence be known. Colonies of hundreds of the pear-shaped, pale-green or black insects feed and reproduce openly on orchids' tender new growth, the undersides of leaves and the bases of flower buds. Aphids are messy guests; their less-appealing calling cards are white skins shed by maturing larvae and clear, sticky waste, or honeydew.

When an orchid becomes overcrowded with aphids, some of the pests develop wings and migrate to new hosts. Unless detected and controlled early, a small infestation may spread through an entire orchid collection.

Sugar-loving ants flock to honeydew-coated orchids. They love the sweet goo enough to protect it by killing insects that prey on the aphids and by moving the aphids from one orchid to another to start new colonies. Killing the ants is essential for aphid control.

To eliminate ants on a potted indoor orchid, prepare a container of insecticidal soap solution using 1 to 2 tablespoons of insecticidal soap concentrate per 1 quart of water. Take it and the infested plant outside, and submerge the pot so that the solution barely covers the surface of the medium. Wait at least 20 minutes and let it drain thoroughly.

To control ants on aphid-infested garden orchids, place enclosed, sugar-based ant bait along the ant trails leading to the plants. Foraging ants carry the bait back to their nests, where it kills the entire colony over several days.

Enlist aphid-eating bugs to battle outdoor aphids. Biological aphid destroyers include green lacewing, parasitic Aphidius wasps and lady beetle larvae. The adult lacewings and beetles deposit eggs on the orchids, and the wasps in the aphids themselves.

Planting shallow-faced, nectar-and pollen-producing perennials near your orchids attracts the adult insects. Good choices include spring-flowering columbine (Aquilegia x hybrida, hardy in USDA zones 3 through 9), summer-flowering English lavender (Lavandula augustifolia, hardy in USDA zones 5 though 9) and fall-flowering fennel (Foeniculum vulgare, hardy in USDA zones 4 through 9).

Ready-to-use insecticidal soap spray smothers aphids on contact. Unlike toxic pesticides, it won't harm beneficial bugs after it dries. Water the plants well, and when the temperature is below 90 degrees Fahrenheit and no sun is on them, spray until the soap drips from all their surfaces. To prevent future infestations, spray every one to two weeks or as often as the label suggests.

Wear protective clothing, including a long-sleeved shirt, long pants, waterproof gloves, safety goggles and a respiratory mask while spraying. Always follow the label directions when using any insecticide.