Explosive. That’s one way to describe the speed at which mite infestations in crops can develop under the right conditions. Those conditions are hot, dry weather—a common occurrence on the High Plains. A spider mite female, for example, can produce 300 offspring during her 30-day lifetime, enabling a mite population to grow from a few individuals to millions rapidly.
The two primary mite pests in the High Plains are the Banks grass mite and the two-spotted spider mite. Heavy infestation in beans can cause leaf loss and even the death of the plant, while mites can cause lighter test weights in corn.
Penn State University Extension entomologists note that most mite populations first develop on grasses and other plants found along the margins of fields. The preproductive female mites then use a silken thread as a kite to migrate into the field1.
Because mite populations can build so quickly, regular scouting of field borders when conditions favor mite development is the best way to catch outbreaks before mites can move further into the field.
Dealing with mites
When you find mites at high levels, what are your control options? A preventive insecticide treatment may be warranted under certain conditions. Colorado State University Extension entomologists recommend asking these questions before applying a preventive treatment.
- Is the crop near tasseling?
- Are a majority of the plants infested with at least small colonies of mites?
- Are the daily high temperatures expected to be above 95 degrees?
- Is part of the field suffering from drought stress?
- Are predator populations (such as predator mites, minute pirate bugs and Stethorus) low?
- Does the field have a history of mite problems? Are two-spotted mites expected to be an issue in the field?
If at least three of these questions receive a “yes” answer, it is likely that one of these treatments will provide an economic benefit.
Even if you can answer yes to three questions, one of the drawbacks to taking a traditional preventive approach is the cost of treating an entire field without the certainty of knowing whether a full-blown outbreak will occur. Those producers with a center-pivot irrigation system, however, have an alternative.
As the Penn State extension experts note, because mites migrate into a field from field boundaries, protecting field margins can be an option. “In large fields, when damage is seen only along the field margins, a spray directed to the injured area and into the field about 100 feet farther may contain the problem.2”
“We have a chemical injection unit, the Boundary Rider, designed specifically to control migrating insects,” says Erik Tribelhorn, CEO of Agri-Inject. “Because mites migrate into a field from the field boundaries, this unit can create a zone of protection.”
According to Tribelhorn, the Boundary Rider mounts on the base beam of a pivot tower—typically the second to the last—and is powered by the tower box. It then injects insecticide up into the pivot, providing a band of insecticide the width of two pivot sections around the edge of the field—the distance that a drifting mite can travel before it must land in the corn.
“When the appropriate miticide is used, you not only eliminate mites in that boundary area, but you create a residual effect that lasts further into the season,” Tribelhorn explains. “The economics are also much more favorable.”
Assuming an effective miticide, with some residual action, costs roughly $30/acre, Tribelhorn calculates that treating 30 boundary acres would cost $900—less than $8/acre to protect the whole field. Treating the entire 125-acre field, on the other hand, would cost $3,750.
“Everyone wants to protect their crops as economically as possible,” Tribelhorn concludes. “If mites are a concern, the Boundary Rider provides a way to accomplish that goal.”
1 Two Spotted Spider Mite on Soybeans and Field Corn, Penn State University Extension, http://ento.psu.edu/extension/factsheets/two-spotted-spider-mite
2 Two Spotted Spider Mite on Soybeans and Field Corn, Penn State University Extension, http://ento.psu.edu/extension/factsheets/two-spotted-spider-mite