Spider mites are common pests for many indoor and outdoor plants. The mites are actually very tiny spiders that can be very difficult to see without a magnifying glass. Spider mites produce fine webs to protect themselves and their eggs. Although they are more often found on evergreen bonsai, spider mites can affect many deciduous bonsai.
Types of Mites
Spider mites are members of the family Tetranychidae and are classified as Arachnids. The most common spider mite, Tetranychus urticae or twospotted spider mite, infests many plants, including bonsai and is a prolific web producer. Some evergreen bonsai can also be infested by spruce spider mites and honeylocust spider mites.
Controlling Via Water
If you don't water your bonsai enough, it can encourage a spider mite infestation. Drought stresses plants can sometimes be more susceptible to spider mites. If you find an infestation, spraying the affected area and washing the webbing away for a week or two can sometimes remove the infestation.
If you are growing your bonsai outdoors and have a spider mite infestation, spider mites have a number of natural predators, including ladybugs and other mites. Releasing these natural predators on your infested bonsai will often result in the predators taking care of the infestation. In many cases, however, the predators require moderate to high humidity and may not survive in arid or semi-arid climates.
In some cases, you can use a special mite soap or even water with dish soap to clean infested indoor and outdoor bonsai. Wash the affected area with soapy water if you catch the infestation early on. For more severe infestations, you may need to bag the infested leaves or branches and prune the branch to remove the mites.
In extreme cases or cases where removing the branch is not an option, such as on older trees or trees where a main growth area is infested, pesticides can be an option for spider mite control. Insecticidal soaps, sulfur based insecticides and a number of different chemical insecticides are all commonly available at home and garden centers and bonsai nurseries.