Spider Mites (Tetranychidae)
Two-spotted spider mites with eggs.
Spider mite damage to corn leaves.
Spider mites are typically a more serious problem in southwestern Kansas, but may occasionally cause economic loss in other areas in droughty years. It should be stressed that miticide applications should be based on the current and projected status of the mite population and not simply damage ratings. The mite history of the field, projected weather patterns, rates of population increase, and the maturity of the crop dictate the need for treatment.
In southwest Kansas fields, where mites have historically been a problem, pre-tassel treatments of a selective miticide (e.g., Comite) may be justified. This is true particularly if the weather pattern is expected to be hot and dry, and corn borer pressure is expected to be heavy enough to require a broad spectrum insecticide treatment. Field history and past experience appear to be the only way to establish whether or not this practice will be advantageous.
Preventive treatments generally are not recommended in areas where mites are not found before tasseling, or where corn borer treatments are not anticipated.
Later in the season (after tassels have emerged) mite populations justify control when large colonies of adult females with eggs and young cover extensive areas along the midribs of the bottom one or two leaves and mites are beginning to colonize other leaves on the plant in significant areas of the field. Like many crops, corn seems to be most susceptible to significant yield damage during the reproductive stages, from tasseling through soft dough.
Coverage is critical to achieving effective mite control. The easiest way to increase coverage is to increase the gallonage applied per acre. Aerial application studies in Texas and Colorado indicate significantly improved mite control at 3 gallons of spray per acre when compared with 1 or 2 gallons, and noticeable improvement with up to 5 gallons per acre. Typically, more than one application is required - check to ensure most eggs have hatched prior to a second application Resistance management should be an important consideration in mite control strategies in areas where mites are a perennial problem. The number of effective miticides is limited, and mites are noted for their ability to develop resistance.
Please refer to the most recent version of the Corn Insect Management Guide for treatment options.
Page last updated 11/04/2013 by J.P. Michaud.