Several species of mites make orchids their breeding grounds, but all fall into two types: spider mites and flat body mites. They can been seen roaming the plant and produce a white silky webbing on the leaves and around the base of the plant at the crown. Mites are very common on cultivated orchid plants, but they are rarely noticeable or troublesome in small numbers. When a noticeable number is visible, swift action is called for to prevent the spread to other plants. Treatment options vary widely. To control a serious infestation, treatments used every 7 to 21 days may be needed for several months.
Water and wash through the orchid plant leaves, roots and planting medium regularly with a strong stream of tepid water. Mites thrive in dry conditions and cannot withstand the water flow from a sink hand-held sprayer or a shower head. A few minutes of intense showering once a week is often sufficient.
Spray commercial insecticides, anti-mite formulations or insecticidal soaps on both sides of the leaves, lower stem and surface of the planting medium. Apply according to label directions using recommended dosing and timing.
Provide biological controls in the form of beneficial insects to eat the mites when you have large-scale greenhouse growing operations. Ladybeetles, wasps and some other types of cannibalistic mites including the phytoseiulus persimilis species are very effective at controlling mites within a closed environment.
Wipe leaves and stems down with cotton wadding drenched in a 3 to 1 mixture of rubbing alcohol and mild liquid detergent. Alternatively, put the solution into a spray mist bottle and apply over the leaves, stem and potting medium. Avoid spraying the top of the stem or near flowers. Allow to dry on the plant out of the sun and away from drafts as drafts can create a cooling effect with the alcohol that can harm the plant.
Repot your orchids when the mite infestation is serious and the silk is layered over the planting medium or egg clusters are visible in the medium. Use a clean pot with good drainage and fresh, sterile orchid potting medium.