The most beautiful house plant can become yellowed, dusty and draped in miniature webbing when spider mites are present. Keeping humidity high and occasionally spraying leaf undersides with water discourages outbreaks of this pest. Plants that are under watered may be more susceptible to spider mite populations.
Spider mites are tiny; depending on the species they can range from only 1/150 to 1/50 of an inch. They do resemble spiders, as the mites have eight legs and lack antennae and wings. The body color ranges from red to maroon-brown or tan; some species are translucent beige. Spider mites spin fine web netting in the areas where they feed. They lay eggs at plant stem bases or on leaves and buds. Adult mites hide under bark or other debris on the ground or within the webbed matrix on the underside of infested leaves. A mite may hatch and grow to adulthood, mate and die within seven days, especially in warm, dry conditions.
These pests have piercing mouth parts that puncture leaves, fruits or roots. They suck the sap out of tissue cells, causing them to turn silvery or yellow in color, often cloaked in a fine web. Sometimes blisters result on tender, young leaves. In species that feed on fruit, the fruits look dry, rough or deformed.
House Plant Damage
The damage caused to house plants varies depending on the plant leaf shape, growing conditions and the number of spider mites present. Individual mite damage is seen as tiny yellow or white speckles. Collective damage resembles a broader, yellowed or bronzed cast across the leaf blade, and soon the leaf falls off. Heavily infested plants may be discolored, stunted or even killed if too many leaves are rendered dry. Although not damage, a fine, dust-like webbing and grain-like egg shells remain on leaves, making house plants leaves look dirty.
Prevention and Control
All spider mites proliferate and feed on plant cells when ambient humidity is low. To slow the growth of the mite population, increase the humidity with an indoor humidifier or place plant pots on a water-filled tray. Spray the foliage undersides with warm water to knock off spider mites, and remove any leaf debris or clinging dead leaves promptly. If the plant leaves are not too small, wipe the leaves on both top and bottom with a soft cloth and soapy water. Use one to two drops of liquid soap in 2 quarts of water. If all else fails, chemicals may be employed, but the plant should be treated out of the house. Sometimes an infested houseplant is best removed and destroyed.
If your house has low humidity (below 20 percent), or you have recurring infestations of spider mites, you may need a new game plan. Consider using large-leaf plants as your house plants, which are easier to monitor and clean. Succulent plants may better tolerate the conditions than a tropical palm. If one corner of a room repeatedly results in any plant being attacked by spider mites, a drying draft may be promoting mite life cycles, or mite eggs may be on your potting soil or carpet debris.