Under warm conditions spider mites move rapidly within the colony area. A resting or quiescent stage occurs at the end of the larval and nymphal stages. A generation may pass in as few as 5 to 7 days in mid-summer, or in a month during cool periods. All active stages of spider mites damage corn by removing juices from infested leaves, causing premature drying that results in loss of leaf tissue, stalk breakage, and kernel shrinking. Damaged leaves become somewhat yellowish and stippled on the upper surface and grayish due to webbing on the undersurface.
Spider mites can be a serious problem on corn, particularly silage and sweet corn.
Reduce spider mite problems by keeping fields, field margins, and irrigation ditches clean of weed hosts. Spider mite populations may increase more rapidly in areas where dust deposits are heavy on corn leaves. Thus, reducing dust may reduce the spider mite problem. Spider mite populations may be held at very low levels by a number of predatory insects and mites, particularly early in the season. Minimizing early-season insecticide applications, which may reduce populations of beneficials, will reduce spider mite outbreaks.