The Itsy Bitsy Spider Mite

This article was originally published on July 26, 2012 and expired on August 26, 2012. It is provided here for archival purposes and may contain dated information.

The Itsy Bitsy Spider Mite

The two-spotted spider mite can be a devastating pest of soybeans in seasons with low rainfall amounts. The mites are about the size of a dust speck. In fact, the easiest way to determine their presence in a field is to shake soybean leaves onto a sheet of white paper. Carefully look at the specks, if they start to move either you have spider mites or you've been standing in the sun too long. A good hand lens can also come in handy.

The other way to identify a spider mite problem is to look for the plant symptoms. The leaves of heavily infested plants will normally have a mottled appearance that will turn from yellow to brown as the problem progresses. Leaves may also take on a dusty or sandblasted appearance.

The problems will often start on the field margins but may appear as hot spots out in a field too. They move via the wind through a process known as ballooning. Mowing roadsides may also speed up their introduction into a field.

A control may be warranted if you are finding live mites, plants are showing discoloration and the weather forecast remains dry. The most common insecticides used as rescue treatments include chlorpyrifos (Lorsban 4E and generics) and dimethoate. In 1988, many fields were treated multiple times due to the continuing drought and residual activity of the products, which lasted approximately a week. In addition, many of the fields in which only border rows were treated ultimately required sprays of the full field.

The best cure for spider mites is rain. A nice general rain or two would stop the spider mite progression. Rains now may be "too little, too late" for the corn crop but could still make a big difference in the soybeans.

Source: N. Dennis Bowman, Extension Educator, Commercial Agriculture, ndbowman@illinois.edu

Pull date: August 26, 2012