Spider Mites
Mite feeding damage on burning bush
Spider mites are so tiny that they can be difficult to see with the naked eye. The easiest way to find them is to shake a suspect leaf over a piece of white paper, then look for moving dark specks. Those moving specks are the mites. Colors may range from red, brown, yellow, to green, depending on the mite species and the time of year. Spider mites are not actually insects; they are classified as arachnids along with spiders, ticks, and scorpions.
Webbing on the infested plants often indicates large spider mite populations. Mites construct webbing to protect themselves and their eggs from temperature extremes and predators. It is important, however, to distinguish between spider mite webbing and spider webs.
Spider mites cause problems to many plants, but in our area the hardest hit are burning bush, spruce, and junipers.
Symptoms and Effects
Spider mites suck plant juices with their piercing, sucking mouthparts. Mites will often feed on the underside of a leaf, protected from direct sunlight. The damaged area will have lighter green to yellow speckles where the chlorophyll has been sucked out of the leaf. This is known as stippling. In heavy infestations, the entire plant may be discolored. Mite damage may be associated with premature leaf or needle drop, especially during hot, dry periods.
Life Cycle
Most spider mites overwinter as adults, hidden in protected areas like bark crevices and under garden debris. During this dormant stage, many mites turn bright red; this is where the common name of "red spider" is derived.
As temperatures warm, the mites break their dormancy and begin to feed. The development of spider mites is directly related to temperatures; during warm periods, they may become fully grown in a week. Mature females may produce over a dozen eggs per day for one to two weeks. This fast development rate and high egg production lead to explosive increases in mite populations under favorable conditions. Spruce and clover mites differ from most other mites in that they are "cool season" mites that occur in peak numbers during spring and autumn.