Aphids & Whiteflies on Orchids

Aphids

• Immature aphids shed tan-colored "skins" that end up scattered beneath infested leaves. You can often locate aphid colonies by looking for these skins. Drops of sugary sap are another tell-tale sign; aphids secrete a sugar-rich liquid called honeydew, and accumulated honeydew often ends up on the ground beneath the leaves. The aphids themselves may feed on the buds, flowers, leaves and other parts of the plant. Usually the wingless adults are green, ranging from yellow-green to blue-green, and they have short tubes that extend from the rear upper part of their abdomen.

Whiteflies

• If a cloud of small white insects swirls around your orchids as you approach, there's a good chance your flowers are infested with whiteflies. These white triangular insects are related to aphids and feature a fine waxy powder covering their wings and body. You can find them on the underside of leaves, where they will ultimately kill the plant if allowed to grow unchecked. Like aphids, they make their living feeding on plant sap.

Aphid Control

• You can catch winged adult aphids with the aid of sticky traps; replace these every one or two months to avoid buildup of dust and dead insects. Sticky traps can also serve as an early-warning system for the arrival of new pests. Mixing vegetable oil or neem oil with a little water and a couple drops of detergent makes an effective aphid-killing solution; do not, however, apply these oils in full sun or at high temperature or humidity. Insecticides like cinnamaldehyde, imadochlorpid, pyridaben, abamectin, pyrethroids and insecticidal soaps offer another option, although these should be used with care and only in the manner dictated by the manufacturer's instructions.

Whitefly Control

• Some gardening stores sell biological control agents for whitefly. The fungus Beauvaria bassiania is one example; when sprayed on the insects, the fungal spores penetrate and eventually kill the insects. Insecticides like diazinon, malathion and various pyrethrins offer another option, although you should never use insecticides and biological control at the same time -- the one will blunt the effects of the other. Removing severely damaged leaves helps prevent the infestation from spreading.