Saturday, January 17, 2015

Houseplant Problems: Spider Mites by Donna Duffy

Two-spotted spider mite, photo courtesy Iowa State University
Spider mites are among the most serious houseplant pests. Left untreated they can multiply rapidly, causing injury, defoliation and plant death. They’re not true insects, but are more closely related to spiders and ticks. The University of Minnesota Extension provides the following information to identify and manage these pesky mites.

Spider mites are oval shaped; yellowish or greenish in color. They’re difficult to see clearly with the naked eye, measuring only 1/50th of an inch. Magnification can reveal amber-colored mite eggs, whitish cast skins, and black fecal specks. To verify spider mite presence, place a sheet of white paper under discolored leaves. Tap the leaves, then watch for tiny moving creatures on the paper.

Spider mites thrive in dry, warm conditions. They make their way indoors in summer and sometimes as hidden guests on Christmas trees and greenery in December.
Mites first feed on the undersides of leaves, then expand their territory as populations increase, moving from stem to stem and onto nearby plants by means of fine webbing. People can also spread them accidentally on their hands, clothing, and watering cans. Always wash your hands and any tools you’ve used after working with infested plants.
Spider mite webs, photo courtesy UMN Extension
Spider mites damage plants by piercing leaf tissue with needle-like mouthparts, feeding on sap. Usually the first sign of spider mites is a mottled or pin-prick yellow discoloration on the undersides of leaves. Webs may also be visible.

Control options: Keep plants well watered to reduce their susceptibility to spider mites. You can take a hose and spray infested leaves and needles to dislodge some of the spider mites. If you want to treat your plants, consider applying insecticidal soap or horticultural oil. Although they are only moderately effective against mites, they are 'soft' on natural enemies and helps preserve any predators or parasites that are present. The product must directly contact the mites to kill them and repeated treatments may be necessary.

For more information, check out Planttalk Colorado Spider Mites on Houseplants.