A hand lens is helpful in identifying these pests on plants.
Aphids, mealybugs, and soft scales use their mouthparts to suck the sap from plants. They can curl, yellow, or stunt leaves and can reduce flower production and stem growth. All three pests also excrete a clear, sticky liquid called honeydew. Black sooty mold fungus can grow on honeydew, covering leaves and making them unsightly.
Aphids, such as the melon aphid, Aphis gossypii, are small (1 to 2 mm long), pear-shaped, soft-bodied insects with two tubelike projections called tail pipes sticking out from their abdomens. Aphids tend to cluster in groups. They feed on young growth, flower spikes, and developing flower buds. Aphids can cause flowers to become mottled and distorted. They are attracted to the fluid excreted by some orchids when they flower, and they are highly attracted to Cymbidiums.
To minimize orchid pest problems, implement such cultural management strategies as prevention, sanitation, and plant inspection. Prevention is the best strategy for managing orchid pests. Proper cultural conditions, such as the correct amount of water, temperature, light, fertility, and humidity, minimize potential pest problems. Many reference books and manuals on orchid culture are available. Be sure to know the cultural practices of specific orchids being grown.
Sanitation is another strategy to prevent orchid pest problems. Remove all plant debris and old orchid medium. Also, remove old leaf sheaths to eliminate hiding places for mealybugs and scales. Inspect plants on a regular basis by looking underneath leaves to detect the presence of aphids and spider mites. If pests are present, use a hard stream of water to dislodge insects and mites.
Insecticides and miticides are another option when dealing with orchid pests, especially when populations are high. Insecticides such as insecticidal soap, malathion, acephate (Orthene), diazinon (Knox Out), chlorpyrifos (Dursban), and bendiocarb (Turcam/Dycarb) control aphids, mealybugs, scales, and thrips.
You can also use biological control to deal with insect and mite pests. Biological control involves the use of a pest’s natural enemies, such as parasitoids, predators, and entomopathogenic fungi. Be sure to control ants, which are attracted to the fluid extracted by orchids, because ants protect aphids, soft scales, and mealybugs from attack by natural enemies. Consult biological control supplier catalogs for natural enemies available for each insect and mite pest.