Stalk borer hatch and migration to new hosts can be predicted using degree days (DD) (41°F base temperature) accumulated from Jan. 1 (Table I).
The simple method for calculating degree days is to subtract the threshold temperature from the average of the daily maximum and minimum temperatures.
Results from daily values are then added together to obtain cumulative degree days. Based on research at Iowa State University, stalk borer egg hatch begins at about 575 degree days and should be complete at 750 degree days. Begin scouting corn when 1,300-1400 degree days have accumulated.
This corresponds with the beginning of larvae moving out of grassy hosts. Determine the need for treatment when 1,400-1,700 degrees days have accumulated.
Cultural Control:
Any weed control method that helps eliminate grasses will reduce the number of potential stalk borer egg-laying sites, reducing the probability of stalk borer damage the next year. Control of grassy weeds is important in keeping a stalk borer infestation from becoming more and more of a problem each year.
Planting date may have some influence on the degree of injury from common stalk borers. Since smaller plants are more heavily damaged, earlier planting may allow corn to escape some of the most severe damage.
If most common stalk borer damage is next to grassy field borders and waterways, burning these areas before eggs hatch has been shown to reduce common stalk borer populations. The best option is to burn these areas in late winter, before the grass begins to grow.
At this time all eggs have been laid, and the soil will be bare and subject to erosion for the shortest time. Also, this timing has the least effect on bird populations that have not yet begun to nest.
Sampling and Economic Injury Levels:
Check corn plants bordering grassy areas to determine the percentage of plants with stalk borer injury when 1,300-1,400 degree days (41°F base) have accumulated since Jan. 1. Examine several sets of 10 plants. Look for feeding damage and dissect damaged plants to see if live larvae are present.
If weedy grasses were common throughout the field in the previous year, the whole field may need to be scouted for common stalk borers. Use the information in Table II to determine the economic injury level
Chemical Control:
To be effective, insecticides must be applied before common stalk borer larvae have entered the stalk. In cases where stalk borers begin feeding on grassy weeds or other vegetation in field edges, control is most effective if timed between 1,400 and 1,700 degree days (base 41°F), which corresponds to first half of the period that stalk borers are migrating from weedy hosts into corn.
If the infestation is restricted to the field margin, use a border treatment. In cases where there is a history of field wide stalk borer damage at a site, insecticides applied to corn and timed for egg hatch may be used to reduce damage.
The disadvantage of this approach is that there is no effective way to sample for stalk borers at this time, so treatments are made without knowledge of whether an insecticide treatment would be profitable that year.
Insecticides may be mixed with fast-acting herbicides being used to burn down early season weeds, or applied several days after use of slower-acting herbicides. Check the label for compatibility of different insecticide and herbicide mixtures.
Bt Corn Hybrids:
Of the currently available Bt corn hybrids, only those expressing the CrylAb Bt protein (YieldGard Corn Borer) have any activity against common stalk borer. The labels for these hybrids indicate that they provide suppression of common stalk borer. Suppression indicates that a lower level of mortality is expected than for insects labelled for control.
Information Sourced From:
University of Nebraska–Lincoln
Office of Research & Economic Development
