Date: April 1989 (Revised April 1995)
Source: NDSU Extension Service Horticulturist
Hot, dry weather conditions are conducive for the development of spider mites on evergreens and broad-leaved ornamentals. Evidence of mite damage on evergreens is a sudden graying or browning of the needles. With heavy infestations, webbing will often be present between the needles and dropping of needles may begin to occur.
Spider mite infestations can be easily detected by holding a piece of white paper under a suspected branch or leaf. Tap the branch or leaf lightly. If spider mites are present they will fall onto the paper and appear as small greenish or red crawling specks.
Spider mite infestations on evergreens can be suppressed by forceful spraying with water at 7-10 day intervals.
One of the most effective miticides available for spider mite control is Kelthane applied according to label directions. Insecticides having activity against spider mites are Orthene, Kelthane, Isotox and/or Diazinon. One or two repeat applications at 1 to 1 1/2 week intervals with either insecticide may be necessary for complete control.
When spraying of tender ornamentals is necessary, the wettable powder formulation of an insecticide should be used in order to prevent foliar injury which can occur when oil base sprays are used on hot days.
For future reference, you may want to obtain a copy of Extension bulletin E-296, "Insect Pests of Trees and Shrubs," which is available at your county office of the NDSU Extension Service.
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