Plant Damage

• Infestations of two-spotted spider mites are a challenge for soybean farmers in several Illinois counties, and a growing problem in corn fields as well. In the home garden, the mites attack vegetable crops including beans and eggplant, flowers, raspberry bushes, fruit trees and house plants. The mites thrive in drought conditions. Plant damage is caused when the mites suck out the fluid from a plant's leaves. That affects the plant's ability to generate chlorophyll. In a severely damaged plant, the leaves turn a bronze color and fall off.
  
  

Economic Impact

• Agricultural yields can be significantly affected by a mite infestation. During a particularly bad year in 1988, Illinois soybean farmers in the hardest hit fields lost 40 to 60 percent of their crops. Keep home gardens and house plants well-watered to minimize the risk of an infestation.
  
  

Identifying Mites

• The two-spotted mite is the most common variety in Illinois. The spruce spider mite infests spruce and juniper, and the Banks grass mite infests turf. All mite varieties are tiny - about 1/10 of an inch long - and go through multiple life stages. They have six legs in the larval stage and eight as adults. Identify the two-spotted spider mite by the dense amount of webbing it produces, and the two green "food balls" visible on either side of the mite's abdomen. Mites don't fly but are adept at travelling from plant tip to plant tip.
  
  

Using Miticides

• Signs of a two-spotted spider mite infestation are most noticeable at the edges of fields and along border rows. During a heavy agricultural infestation in 2005, the University of Illinois' Integrated Pest Management Department issued a bulletin cautioning that populations had boomed in soybean fields where miticides were applied repeatedly. The number of mites more than tripled - to 975 insects per five leaves - in one plot treated twice with Dimethoate 4E. The department advised using two different miticides rather than applying the same brand twice. Treatments for soybean aphids also increased mite populations. Use of pesticides such as Sevin in the home garden may kill the natural predators of mites and significantly worsen an infestation.
  
  

Other treatments

• Some of the best agricultural results were reported in fields where no miticides were used. "It is very interesting - and important - to note the significant decrease in numbers of spider mites in plots that have not been treated this summer," noted University of Illinois researchers Kevin Steffey and Mike Gray in the 2005 article. "We are not certain yet what has caused this reduction, but we can speculate that in the absence of miticides, natural enemies may be suppressing spider mite populations." A mite-eating species of lady beetle, the "Stethorus" species, is helpful in the home garden as a biological control.