Answer: Spider mites are one of the more difficult groups of landscape pests to control. Infestations are easiest to control when detected early, before the mite populations have reached very high levels.
Water sprays should be directed upward against the lower leaf surfaces, and the technique will need to be repeated on regular intervals. Low populations of spider mites may be held in check by naturally occurring predatory mites which feed on both eggs and active stages.
Elimination of moderate to heavy infestations of spider mites usually requires the use of specific pesticides known as miticides. Some, but not all, insecticides will also control mites. Some kill only active mites while others also kill eggs. Always read and follow the directions accompanying the product you are using. Some miticides may harm or discolor certain types of landscape plants.
Good spray coverage is essential when applying miticides. Thoroughly wet the foliage and try to contact as many mites as possible, paying particular attention to leaf undersides where most mites are living. In most cases, two or more applications at 5-10 day intervals will be needed for satisfactory control. Spider mite eggs that have not yet hatched are unaffected by most miticides; the same may be true of larvae and nymphs that are molting. During molting, spider mites remain inactive beneath the former skin, which serves as a barrier against insecticides. The quiescent mites also do not feed, rendering products that kill by ingestion temporarily ineffective. Consequently, if only one application is made, some of the mites may survive and the infestation will persist.
Effective homeowner options include Kelthane, horticultural oils, and insecticidal/miticidal soaps. Horticultural oils and soaps can be effective alternatives to conventional miticides, but require thorough coverage so that all mite stages are contacted. These products will also kill aphids.
Insecticides recommended for use against crawling pests include acephate (Ortho Bug-B-Gon, Ortho Systemic Insect Killer or Ortho Orthenex Garden Insect & Disease Control Concentrate). Read and follow all label directions and precautions before using.
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