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Cass County Extension

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Spider Mites

Are the needles on your evergreens turning a dull gray-green in color? This may be evidence of a spider mite infestation. As the number of mites increase, webbing can often be found between the needles and dropping of needles may occur.

Every year my marigolds seems to get infested with mites. The plants take on a mottled or spotted look with webbing between the leaves. As the infestation get worse, the leaves will turn yellow or brown. If the mites aren't controlled they may kill the plants.

Spider mite infestations can be detected by holding a piece of white paper under a suspected branch or leaves. Tap the branch or leaves lightly. If mites are present they will fall onto the paper and appear as tiny crawling specks.

Control may be accomplished by hosing down the plants every 7-10 days with a forceful water spray or by spraying with an insecticide. One of the most effective miticides available for control is Kelthane applied according to label directions.

Insecticides such as Malathion or Diazinon will also give control. Two or three repeat applications at 7-10 day intervals are necessary for good control. When spraying flowers, the wettable powder formulation of an insecticide should be used in order to prevent leaf injury, which can be caused when oil base sprays are used on hot days.


Todd Weinmann, Extension Horticulturist & Master Gardener Coordinator
Phone: (701) 241-5707
E-mail: todd.weinmann@ndsu.edu

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