News release: Spider Mites, Part II

Tim Baker, MU Extension Horticulture Specialist
102 N. Main, Suite 1, Gallatin, MO 64640

Release Date: July 5, 2018
Headline: Spider Mites, Part II

In my last column, I mentioned that spider mites were already becoming a problem for some growers. The hot and dry weather has favored their rapid development, and commercial growers and gardeners should be watching for their damage.

When I was in Southeast Missouri, I saw spider mite damage in watermelons almost every year. Sometimes, the mites were caught in time. Other times, their feeding was devastating.

Occasionally, watermelon fields could show significant damage, but still recover. I remember one field in particular that was very hard hit, and I told the grower that he should spray a miticide immediately, or he would run the risk of losing his crop. Fortunately, that field was caught in time.  The grower applied a miticide that day.  The mites were stopped, and by the next week, the field was starting to “green up” again.

Another grower was not so fortunate. I had previously showed him how to identify spider mites, so he knew what to look for. I was driving by one of his fields one day, and the plants were totally dead. So I stopped by his house to see what had happened.

It turned out that the previous Friday, he had found the mites starting. Unfortunately, he could not find any miticide locally to spray. So he sprayed an insecticide that was labeled for mites, in addition to insects. This may have killed some mites, but it also killed the beneficial insects that were helping to control the mites.

Unfortunately, the spider mites recovered before the beneficial insects did. By the time I saw the field, early the next week, the plants were gone. It can happen that quickly, given the proper conditions.

So a dedicated miticide is critical. These products are specifically targeted toward mites, and are not supposed to harm beneficial insects, including bees, when used as directed.

Good coverage is critical to successful mite control.  Spider mites feed on the lower surfaces of leaves, and it is important to get your spray up under the leaves where it can contact the mites.

If you suspect that you may have spider mites in your crop, and would like help identifying them, please do not hesitate to give me a call.