Orchids are prone to infestations of several kinds of insects, some of which are very damaging to your plants. Preventing pest infestations takes less work than treating them. Checking your orchids regularly will allow you to control pests while infestations are small and simpler to treat. Poor growing conditions increase susceptibility to pests. Insects also may arrive on new plants, so keep newcomers quarantined before adding them to your collection.
Experts at South Caroline State University identify scale insects as the most important orchid insect pest. According to Paul J. Johnson of South Dakota State University, "Scale management is usually a protracted and serious effort, and never much fun."
Scales appear as raised dots and may affect all parts of the plant. Scale insects secrete "honeydew," a sticky substance that is often the gardener's first clue that there is a problem. Treat small scale infestations by dipping a cotton swab in 70 percent isopropyl rubbing alcohol and applying it to the insects individually. More extensive infestations require the use of insecticides. Regardless of the extent of infestation, isolate affected plants, as scales can move between them.
Mealybugs may significantly weaken orchid plants. The insects are oval-shaped, pale in color and have long fibers at the backs of their bodies. Mealybugs also produce honeydew, and sticky patches under leaves may be the first sign of infestation. Control small infestations with applications of 70 percent isopropyl rubbing alcohol, but established infestations require the repeated application of insecticides. Mealybugs also hide in cracks and under the lips of pots, so isolate infected plants.
Spider mites are very small, difficult to see and are often first spotted by the damage they cause. Mites suck the juices from leaves, which become dry and silvery in appearance. Chrysanthemum extract and insecticidal soap may control infestations. However, prevention is also a key. Mites prefer dry conditions, so increasing the humidity and air flow around your plants discourage mites from multiplying.
Aphids pierce plant tissue and drain fluids from the plant in addition to carrying diseases that affect orchids. Control aphids using insecticidal soap, rubbing alcohol or chrysanthemum extract.
Whiteflies look like small white moths. They feed on orchid leaves and lay their eggs inside of the leaf tissue, where the larva feeds on the plant's juices. Whiteflies also secrete honeydew, which may promote fungus growth. Control whiteflies using sticky traps or repeated insecticide spraying.
Fungus gnats are primarily a nuisance and do not harm orchids. They are small, with long legs and antennae and gray-black wings. Although harmless, infestations may indicate poor plant care, since the gnats are attracted by fungus growing on over-watered soil. To prevent fungus gnats, allow growing medium to dry between waterings and use fertilizer sparingly. Control fungus gnats with sticky traps.