Mites are one of the common, but few, pests that affect orchids. Two main groups of mites attack orchids: flat mites and spider mites. Though their appearance and feeding action is somewhat different, the treatment for them is the same. Appropriately moist cultural practices will keep mites at bay and when an infestation flares, swift and vigilant treatment is called for to prevent the spread of mites to other orchids and plants.
Place the affected orchid plant under a tap or shower flowing with tepid water once a week to wash the mites away. Wash from mid-stem down when in bloom or over the top of the plant when out of bloom. Use a hand sprayer if available to wash the mites off the underside of leaves and the top of the planting medium.
Spray orchid plants with a diluted mixture of rubbing alcohol and gentle liquid dish soap using three parts alcohol to one part liquid dish soap. Cover all foliage including the underside of the leaves. Blot the excess alcohol mixture off the leaves with a paper towel, to prevent over-cooling. Repeat this once every 10 days to two weeks until the mites are gone. Rinse the plant in tepid water before reapplying the solution.
Repot orchids where the mites may have compromised the planting medium. Remove all the old bark and wash the pot with hot water and soap, rinsing well. Rinse the plant and roots gently in tepid water to wash away any mites or eggs. Replant the orchid and water in well.
Purchase and apply an insecticidal soap safe for orchids, to help control the most stubborn infestations. Look for a product that contains synthetic pyrethrin, and apply according to label directions over washed orchid foliage.