Scout for Twospotted Spider Mites

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Twospotted spider mites are probably the most common spider mite species to damage ornamental plants, fruits, vegetables, and others. Twospotted spider mites are widely distributed in the United States and feed on over 180 plant species. Twospotted spider mites pierce host plant leaves with their sharp, slender mouthparts. When they extract the sap a chlorotic spot appears. High mite populations cause leaves to become bronze or gray as these chlorotic spots, called stippling, accumulate. Plants will drop damaged leaves and may die. Mites also spin silk webs that can cover leaf surfaces and accumulated feces, exoskeletons, and other debris.

Twospotted spider mites and webbing on a butterfly bush leaf. Photo: SD Frank

Twospotted spider mites and webbing on a butterfly bush leaf. Photo: SD Frank

Twospotted spider mites are common on roses, daylilies, hollyhock, marigold, butterfly bush, Solomon’s seal, and many other annuals, perennials, and shrubs. Twospotted spider mites are most active in hot dry weather which I imagine will be here any day now. Area Specialized Agent Danny Lauderdale suggested nurseries begin monitoring susceptible plants soon as the weather warms. Landscape plants are also susceptible and should be monitored. Look on the undersides of leaves for webbing, eggs, shed skins, and mites. An efficient way to monitor is to beat plant foliage on a paper plate or other white surface. Mite will be easily distinguished from dirt and other debris because they will be moving. Check plants weekly as populations can outbreak very quickly. Throughout the season look for stippling damage on leaves and focus scouting on plants that have been damaged in previous years.

Twospotted spider mite damage on butterfly weed, Asclepias tuberosa. Photo: SD Frank

Twospotted spider mite damage on butterfly weed, Asclepias tuberosa. Photo: SD Frank

The best management option for spider mites is to plant less susceptible plant species in areas that are hot, dusty, or stressful. Nitrogen fertilizer can induce mite outbreaks by making plants more nutritious to feed on.

Spider mites have many predators that often keep them under control. These include predatory mites, minute pirate bugs (Orius spp.), lacewing larvae, lady beetles, and others. Disrupting natural enemies with insecticides, such as mosquito fogging, often causes spider mite outbreaks. Imidacloprid and other neonicotinoids can also lead to spider mite outbreaks.

In many cases mite populations can be reduced with insecticide soap or horticultural oil. Thorough application of pesticides to the underside of the plant foliage is essential for good control. Most insecticides do not kill spider mites because mites are not insects. There are many miticides available that target specific aspects of mite physiology. These products are also safer for beneficial insects than broad spectrum insecticides. Consider miticides from the Southeastern US Pest Control Guide for Nursery Crops and Landscape Plantings.