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Arrival of cool weather brings out cool season spider mites

What are spider mites?  Most common trees, shrubs and flowers are susceptible to injury by one or more species of spider mites. Two spotted spider mites feed on a wide variety of plants.  Their capacity to injure plants is representative of other species.

Summer is over. Why worry about spider mites now? Even though you can put away your mite controls for warm season mites on most flowering plants and shrubs, mites that feed on spruce trees, rhododendrons, and other broad leafed plants can be infested by the spruce spider mite and the southern red mites when the daily high temperature is below 85˚F. Spider mites are small 8 legged creatures that are more closely related to common house spiders than insects.

Use of some insecticides, like carbaryl and neonicotinoids, in mid- summer to protect plants against bagworms, and lacebugs can kill the predators that keep these cool season mites under control.

Inspect your plants for spider mites.  Look for plants that begin to fade in color and appear as if covered in dust or appear bronze or covered in webs.

How to control spider mites

If you just have one or two affected plants or small parts of a plant affected, consider pruning or removing the infested part and spraying the remaining plant parts with a strong shower of water from your garden hose.  This will knock off some mites, and if you do it repeatedly over a week or two, it could encourage the growth of a fungus that kills spider mites.

Apply a solution of 2% insecticidal soap, horticultural oil, or neem oil to kill spider mites if hosing down your leaves is not an option for your plants.  Do not use oil or soap on blue spruce, as this will turn leaves green.

If your plant is dripping with mites and webs and all else has failed, you can use a miticide.  Homeowner products with the active ingredient bifenthrin can kill spider mites and hold them back for as long as a month before the spider mite population comes back. Professionals have a wider choice of products to choose from. For more information on specifics see our bulletin on managing spider mites in the urban landscape.

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