We are receiving increased reports of spider mites and recommend scouting, careful identification of the species present, and, if necessary, timely treatment. Insecticide treatments for other insects such as western bean cutworm or rootworm beetles can provide an opportunity for spider mite populations to explode in some fields.
Mites do not cause major economic damage every year in Nebraska. Several factors, which fluctuate from year to year, strongly influence spider mite numbers. Probably the most important of these factors are weather, natural enemies, and pesticide use. Overwintering sites that are close to corn and soybean fields, especially grasses, wheat, and perhaps alfalfa, also may increase the possibility of mite invasion.
Dry, hot weather favors mite reproduction and survival, especially if accompanied by drought stress in the crop. When the weather in June, July, and August is especially hot and dry, mites can reach damaging numbers in most corn and soybean growing areas of Nebraska. Major mite infestations are more likely to occur in central and western counties that normally experience less rainfall. Sandy soil types also may contribute to spider mite problems in these areas because crops grown on these soils are more likely to experience drought stress even when irrigated.
For more information on identifying and managing spider mites in your fields, please see 2016 stories:
- Identifying Spider Mite Damage and the Species Responsible
Two species of spider mites, the Banks grass mite and the twospotted spider mite, commonly feed on Nebraska corn. Banks grass mites (BGM) feed almost exclusively on grasses, including corn, small grains, and sorghum. Twospotted spider mites (TSM) not only feed on many species of grasses, but also on soybeans, fruit trees, and a variety of vegetables and ornamental plants.
This story includes photos and a chart to aid in differentiating the species. Proper identification of the mite species present in a field is essential for making control recommendations and selecting an appropriate pesticide. This is because colonies of TSM generally are more difficult to control than BGM, and some insecticides used to control other pests are more likely to increase TSM numbers than others. Read the rest of the story.
Most pyrethroid and organophosphate insecticides used in corn and soybeans have severe, detrimental effects on spider mite predators. Additionally, pesticides differ a great deal in their effects on BGM and TSM. Some cause little mortality of either species, while others are somewhat toxic to BGM. Fewer are toxic to TSM.
Thus, great care should be taken to evaluate the benefits of an insecticide application before any material is applied for insect control in a field that also has spider mites. Even small numbers of mites can rapidly increase to damaging levels when conditions are favorable. In many cases, it is an earlier treatment for western bean cutworms or corn rootworm beetles that leads to a later spider mite problem in corn.