Part 2, Section 2: Corn Pest Management
Corn Pest Management
INSECTS
Insect pest populations, greatly influenced by weather conditions and other natural phenomena, cause 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 fields and making control decisions.
Crop rotation provides effective control of corn rootworms and helps reduce several other corn pests. Although the Midwest has seen a neew variant of the western corn rootworm that overcomes the benefit of crop rotation by laying its eggs in soybean fields, we have not yet seen this newer insect type in Pennsylvania. Minimum-till and no-till systems and poor weed control increase the incidence of armyworm, cutworm, and stalk borer. In most cases, eliminating grassy weeds at least 2 weeks before planting reduces the possibility of these 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 are not profitable.
Recently, biologically engineered corn hybrids that produce a delta-endotoxin using a gene from the bacterium Bacillus thuringiensis began providing a new method for managing European corn borer and root injury from corn rootworm. This new technology offers cost-effective crop yield protection that could not be obtained using conventional insecticides. Because of its low relative cost and high degree of effectiveness, Bt-corn is gaining popularity rapidly. Because Bt-corn is an easy and cost-effective method of managing both these insects, however, there is an increased risk that the pest will become resistant to the toxin if it is overused. Growers who choose Bt-corn hybrids will be required to implement a resistance management program to minimize the rate of resistance development. For more information on using Bt-corn hybrids, see the insect resistant (Bt) corn varieties section, above.
A new front on managing insect pests in corn is seed treatment technology. Although hopper-box treatments have been available for a long time, commercially-applied seed treatments using a new class of chemical has become popular. This newer insecticide class, neonicitiniods, has three compounds that are available for corn. The first material that was available as a commercially applied seed treatment, imadicloprid (Gaucho), was the initial compound growers could use. However, with the introduction of two newer compounds, thiamethoxam (Cruiser) and clothianidin (Poncho), imadicloprid has been relegated to a hopperbox treatment now known as Concur or Latitude. The two products now commercially applied, Cruiser and Poncho, are abailable each at two rates, 0.25 mg a.i. per kernal and 1.25 mg a.i. per kernal. All rates provide protection against the usual soil insect pests. At the higher rate, both seed treatments add corn rootworm larvae and billbugs to their labels. However, studies have shown that they only work well against low to moderate populations of the rootworm larvae; they do not work well at intense rootworm pressure.
The first step in managing corn pests is to know when the pest is present in your area. Figure 2.2-1 illustrates the approximate timing of corn pest occurrences in Pennsylvania. The presence of a pest can vary within the presented range, depending on the location in the state and on local weather conditions.
See Table 2.2-21 for a quick reference to insecticides recommended for corn insect control, and Table 2.2-22 for specific rates, restrictions, and other information. Table 2.2-23 lists herbicides that are compatible with selected corn insecticides.