Factsheets from Pennsylvania State University Insect pest populations, greatly influenced by weather conditions and other natural phenomena, result in variable crop losses from year to year. Since losses from insects may be high one year and of little consequence the next, growers should use a system for monitoring the fields in making control decisions. Crop rotation provides effective control of corn rootworms and helps reduce several other corn pests. In most cases, elimination of grassy weeds at least 2 weeks before planting reduces the possibility of common stalk borer and armyworm problems. Armyworms also can be a serious problem in fields where corn is planted into wheat stubble or into a rye mulch.
Some varieties have genetic resistance or tolerance to European corn borer.
Insecticides can be applied to reduce pest populations, but unless the predicted losses are greater than the cost of application, such applications will not be profitable. The first step in managing corn pests is to know when the pest is present in the area. Figure 1 illustrates the approximate timing of corn pest occurrences in Pennsylvania. The presence of a pest can vary within the presented range, depending on location in the state and on local weather conditions. See table 1.