Grasshoppers and Winter Wheat

Reports are coming in of large grasshopper populations throughout South Dakota this summer and early fall. While these populations will continue to decline, there is still the possibility for significant populations to remain until after the first hard frost.

In areas where grasshopper populations have been consistently high, it is important to scout emerging winter wheat for injury, and manage grasshopper populations when necessary. The limited amount of green vegetation in the fall makes the newly emerging winter wheat very attractive to grasshoppers. Grasshoppers are capable of causing stand loss to emerging winter wheat by clipping the plant back due to the limited amount of foliage on seedlings. This type of injury will be more noticeable on the field edges as grasshoppers reside in the vegetation along field margins. Before and after planting, farmers should monitor fields and pay close attention to the margins to determine grasshopper population densities.

Grasshopper management options before planting
Management should be considered if grasshopper populations in the field and non-crop borders are in the range of 11-20 grasshoppers per square yard prior to planting. Management options to consider include:

• Delay planting in areas where there are high grasshopper populations to reduce the time that grasshoppers will be feeding on the emerging wheat.
• When there are increased population densities in areas surrounding the field, double seed in a strip that is between 60-120 feet wide around the field margin. As grasshoppers move into the field they will feed on the emerging wheat, but the increased plant stand around the margin will slow the movement of the grasshoppers into the field. The increased plant stand will compensate for the lost seedlings and allow for a reasonable stand to exist after grasshoppers have finished foraging for the year.
• Insecticide seed treatments are labeled for grasshopper management in wheat, and can provide protection during emergence. For grasshoppers, treated seed can be planted to the field margins in strip that is 60-120 feet wide, or it can be planted to the entire field. For effective management of grasshoppers the highest registered rate of the product should be applied to the seed. 
• Foliar insecticide sprays may be applied to the non-crop field margins to prevent the grasshoppers from moving into the wheat fields. Before selecting an insecticide, check the label to ensure that it can be sprayed on non-crop areas. 

Grasshopper management options after planting
If grasshopper populations are observed causing severe defoliation or clipping in newly emerged wheat, it is important to determine if the populations are above 11-20 grasshoppers per square yard. Additionally, determine how far into the field the grasshopper populations are. Management options to consider for emerged wheat include:

• If the injury and grasshoppers are only present around the field margin a foliar application of insecticide to that area may be sufficient to reduce further injury. It is important to remember that there will be little residual activity of the foliar insecticides due to the limited leaf area of emerging wheat.
• If injury to the field margins is severe due to heavy grasshopper feeding pressure, it is possible to replant those areas later in the fall after the first hard frost occurs. At this time grasshopper populations will have rapidly declined.

Source: Adam J. Varenhorst, South Dakota State University