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Spider Mites

by Karen Miller, Master Gardener Entomology Specialist

There are bad bugs, and then, there are bad, bad bugs. Spider mites are bad, bad, bugs. Spider mites are members of the Tetranychidae family and are classed as a type of arachnid. They are relatives of insects that also include spiders, ticks, daddy-longlegs and scorpions. The order name, Acari, is from the Greek word Akari which means a small thing. Spider mites are less than 0.04” in size, they are definitely small things. Spider mites are often difficult to see with the unaided eye. They range in color from red and brown to yellow and green. Color depends on the species; also the spider mite can change its appearance with the change of seasons. Spider mites go through four life cycle stages: egg, larva, nymph and adult. The adults lay small clear to yellowish round eggs which are often suspended in a fine web of silk on the underside of the host plant’s leaves. The adult spider mite has eight legs; the larval stage has only six and will develop the other two as they go through the molting process.

Spider mites just love hot, dry weather. Temperatures around 80* are considered optimal conditions for the two-spotted spider mite, most common in our area, to hatch in as little as three days, becoming sexually mature in as little as five days. One female can lay up to 20 eggs per day and can live for two to four weeks, laying hundreds of eggs. One single mature female and spawn a population of a million mites in less than one month.

mites in a month or less. Spider mites are considered a serious pest inside on houseplants and on many plants around the yard. They congregate on the underside of the leaf where they feed off of the plant fluids while stealing the plants chlorophyll in the process. Visible signs of spider mite damage include webbing and white or yellow speckles on plant leaves. A severe infestation can cause leaves to become discolored, giving a gray or bronze look to the plant. Leaves and needles can become scorched and drop prematurely. Spider mites frequently kill plants or cause serious stress to them. Now that we have massive generations of spider mites, how do we get rid of them? One reason the spider mite has become such a problem in our yards and gardens is the use of insecticides that destroy their natural enemies. Because of their rapid reproduction rate, the spider mite can adapt quickly to resist certain pesticides especially when used over a long period of time. Miticides or acaricides are a good chemical control of spider mites. These are pesticides developed specifically for spider mite control. Be aware though, miticides do not affect the eggs, so repeat the application again in approximately 10 to 14 days for complete control. Bottom line…Stressed or weak plants are the likely target of the spider mite. Plants stressed by drought can produce changes in their chemistry that make them more appealing to spider mites. Adequate watering of plants during dry condition can limit drought stress. Just a periodic hosing of your plants with a forceful jet of water can physically remove and kill many mites.



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