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Last week I received a call from a watermelon grower who suspected that he had spider mites. While this seems a bit early to be seeing spider mite problems, we have experienced hot and dry weather recently, which favors mite growth and reproduction.

The grower that I visited showed me melons with classic mite symptoms: leaves had ill-defined yellow spots where the mites had been feeding. Upon inspecting the leaves with a hand lens, I saw high numbers of mites.

A second field of watermelons was not showing symptoms to any degree at that point, but I did find a few mites. The grower decided that it was time to spray. A wise decision. Under hot, dry conditions, spider mite populations can literally explode and take over fields extremely quickly. They have been known to destroy entire melon fields.

Mite damage may look like a disease problem. The leaves turn yellow and start to die. Often growers remark to me that when they see these symptoms, they step up their fungicide sprays, but it doesn't help. Of course in this case, a fungicide spray program won't help, since you're dealing with a mite, not a fungus. Miticides are what is needed.

Spider mites can attack almost any plant, including ornamentals in your front yard. I've seen them on ornamental bushes, apple trees, peach trees, cantaloupes, and watermelons. There are different species of mites which attack different plants. The mite usually seen in watermelons and cantaloupes is the two-spotted spider mite. This is the same mite that can attack cotton, and is often referred to by growers as the "red spider." The grower that I visited last week also reports that he has already seen spider mites on his cotton this year.

Sometimes, the problem is worse in fields with heavy insecticide use. Some insecticides are labeled for mites, but over the past several years we have seen situations where the beneficial insects that usually control the mites are killed off by these insecticide/miticides, and then mite populations explode. In these situations, we especially recommend a straight miticide, such as Kelthane, which should not harm the beneficial insects. Quick action is often necessary, as mites can cause significant damage in short order. Another advantage of using a product such as Kelthane is that it should not be harmful to bees, which are critical for melon production.

To check for spider mites, a hand lens is useful. The female is oval shaped and about 1/50 inch in length. The male is smaller. They come in many colors: red, reddish yellow, yellow, greenish, or blackish. They have two large spots on each side of the body. Sometimes you can see small webs where eggs have been laid.

If you suspect spider mites, but can't tell for sure, give me a call. I'll be glad to check your field. Mites can be devastating and can destroy fields rapidly. It's best to catch them in the early stages when control is easier.


		Sarah Denkler, Horticulture Educator University of Missouri Extension P.O. Box 160, Kennett, MO 63857 573-888-4722 Denklers@missouri.edu Updated 04/18/08

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