Issue 1, April 18, 2011

Spruce Spidermite

Spruce spidermite and its relatives, pine mite, arborvitae mite, and juniper mite, actively feed during early spring and early fall. They spend the summer as eggs on the host. Most miticides are effective primarily against active, feeding stages, providing little control of eggs.

Spidermites are tiny relatives of spiders, having eight legs and spinning very fine silk. They are so small that they are barely visible to the unaided eye, a hand lens is needed to see them on the foliage. Scout by holding a piece of white paper under a branch and striking it sharply with your hand or stick. This knocks some of the mites onto the paper where they can be easily seen. Spidermites are greenish-gray and move relatively slowly. Predatory mites are commonly red and move quickly compared to the spidermites. These predatory mites feed on the spidermites; numerous individuals will likely control the spidermites, making spray application unnecessary.

A spidermite sucks the contents from several adjacent cells, removing the green contents, resulting in a white spot on the needle. These cells soon die, causing that spot to turn brown. The mites feed separately from each other, leaving green, healthy tissue between the feeding spots. This type of damage is caused stippling, being a number of tiny dots. In art, the shaded area of a drawing caused by numerous little dots is called stippling and is the source of this damage designation. From a distance, the brown stipples meld with the green areas of the needle, resulting in a bronze appearance to the foliage.

Spruce spidermite and its relatives are actively feeding in southern Illinois from about mid-March through April. They feed in central Illinois from early April through mid-May and in northern Illinois from mid-April through May. Before applying a miticide, verify that mites are present by scouting with the white paper method described above. Spray a labeled miticide or acaracide such as acequinocyl (Shuttle), bifenthrin (Talstar, Onyx), insecticidal soap, spiromesifen (Forbid), or summer spray oil to obtain control. (Phil Nixon)

Phil Nixon

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