Small Insects With Webs on Orchids

Hosts

• Of all the identified plant species, an astonishing one of every eight plants is an orchid (Orchidaceae family). Encompassing more than 30,000 named species, orchids are broadly categorized into two types: terrestrial orchids, which generally grow as perennials in U.S. Department of Agriculture plant hardiness zones 9 through 12, and include the genera Phaius and Paphiopedilum; and epiphytic orchids, which typically grow in USDA zones 10 through 12, and include the genera Cattleya and Phalaenopsis. Regardless of type, genus or species, all orchid plants may host mites.

Mites

• Various mites are among the primary pests of orchids, particularly the two-spotted spider mite (Tetranychus urticae). The webs they spin help keep them hidden and inaccessible by predators, not to ensnare insects for food. Orchids respond favorably to humid conditions, and they are susceptible to spider mites only in hot, dry environments. The mites can sometimes only be seen with a magnifying hand lens, where you can identify them by their greenish bodies that have a dark spot on each side. Although the two-spotted spider mite indiscriminately feeds on different orchid types, some mites, such as the Phalaenopsis mite (Tenuipalpas pacificus), are host-specific.

Damage and Control

• Mites feed typically on the undersides of leaves, where they pierce soft tissue and siphon plant sap. Since chlorophyll is removed with the sap, evidence of mite predation may appear as yellow stippling across leaves or larger, white areas. Affected leaves are damaged permanently, and they will not green up again. Leaves that sustain heavy feeding may drop prematurely. Eliminating the dry environment that mites favor is the most practical method of control. Increase the humidity around your orchids by misting the foliage daily or setting plant pots on a water-filled pebble tray, making sure the pots do not touch the water. Because orchids are sensitive to many chemicals -- even those that are labeled for orchid use -- an effective and milder control for mites is to use a premixed horticultural oil or insecticidal soap that you spray on the foliage and wipe off gently with a soft cloth.

Considerations

• If you find mites on one orchid plant, it’s likely that other plants are also affected. Although mites are typically wingless, winged forms may appear that fly to other plants and establish new colonies. Although miticides are available for orchid use, they may damage your plants. Mites easily develop resistance to certain chemicals, which requires you to rotate products, sometimes as often as every three to four applications. Often, this barrage is too harsh for many sensitive orchids. However, if you use soaps or oils, there is not a resistance issue, because these products kill the mites by suffocating them.