The good news is that as of just a few days ago, Christian Krupke had only a couple confirmed reports of spider mites attacking soybeans in Indiana. The two-spotted spider mite is a problem in dry years. Krupke is a Purdue University Extension entomologist.
The bad news is that if dry weather persists, the spider mite problem could explode, he says. That's what happened in 1988, one of the worst drought years in Indiana history. The drought that year developed very early.
What you're looking are soybeans with bronzed leaves, usually first apparent along the edges of the field, he says. They probably won't be around the entire field at first, either. To confirm you are dealing with mites, take a piece of white paper or other white material and put it below a plant. Shake the plant over the white surface. If mites are present, you will see a multitude of black specks moving across the paper.
The problem with spider mites is that it can spread across a field quickly, he notes. That's why you need to keep a close eye on fields. The problem can show up rapidly if dry weather persists. If you elect to spray, it can be by ground or by air. If you catch it early enough, while the problem is just along the field borders, Krupke recommends a ground application. He also recommends spraying around the entire field border. Areas that are still green and haven't turned bronze yet in appearance may have the mites, and may have just not reached the stage of damage to exhibit the tell-tale bronzing that denotes spider mites are at work.
There are two insecticides that will get the mite. Neither one are used in large quantities in most years, so if spider mites explode as they did in 1988, it may be tough to find materials to control them. There are miticides that will work, but they are not labeled for soybeans, and are expensive. However, if the problem becomes severe enough, Krupke and Fred Whitford, director of Pesticide Programs for Purdue, can seek an emergency permit for sue of these products in soybeans.
"That's why we need to hear from you if you find mites in your soybeans,"Krupke says. "It can take a couple of weeks to get the permit. There is paperwork involved. And we can't act until it is an emergency. So the sooner we can get started on the application once we know there is a problem, the better."