2018 Western South Dakota Grasshopper Forecast Back »

Written collaboratively by Adam Varenhorst, Patrick Wagner, Philip Rozeboom, Laura Edwards, Amanda Bachmann, and Erica Anderson.


In South Dakota, there are several species of grasshoppers that can have a negative impact on rangeland health. The United States Department of Agriculture’s (USDA) Animal Plant Health Inspection Service (APHIS) conducts an annual survey to monitor grasshopper populations in Western South Dakota. The focus of these surveys is adult grasshoppers and the previous year’s survey can be used as a prediction tool for the upcoming season.

In 2017, the grasshopper populations in Western South Dakota were lower than those observed in 2016. There were still a few isolated areas where the populations exceeded the threshold of 8 or more adult grasshoppers per square yard in Lyman, Gregory, Meade, Corson, Dewey, Lawrence, Bennett and Jackson counties (Figure 1).

Image of South Dakota where green areas indicate Forest Service, light red colors indicate Bureau of Indian Affairs, green circles indicate areas with low grasshopper populations, orange circles indicate medium grasshopper populations and red circles indicate high grasshopper populations that exceeded thresholds.
Figure 1. Map of 2017 grasshopper abundance for Western South Dakota. Green circles indicate grasshopper populations that were below threshold, orange circles indicate grasshopper populations that were approaching threshold, and red circles indicate grasshopper populations that exceeded threshold. Courtesy: USDA APHIS.
Image of South Dakota where green areas indicate Forest Service, light red colors indicating Bureau of Indian Affairs, green circles indicate areas with low grasshopper populations, orange circles indicate medium grasshopper populations, and red circles indicate high grasshopper populations that exceeded thresholds.
Figure 2. Map of 2016 grasshopper abundance for Western South Dakota. Green circles indicate grasshopper populations that were below threshold, orange circles indicate grasshopper populations that were approaching threshold, and red circles indicate grasshopper populations that exceeded threshold. Courtesy: USDA APHIS.

The two consecutive years of drought as well as the 2017 spring may have played a major part in the reduced adult populations that were observed during the survey. Many of the observed populations were still nymphs in late July when we would normally expect to see adult grasshoppers. Although development was behind schedule, the first 28°F frost for most of Western South Dakota didn’t occur until the first week of October (Figure 3). This would have given the grasshoppers plenty of time to reach maturity and lay eggs. In addition, there were areas of South Dakota where the frost didn’t occur until the third week of October (Figure 3). In general, the 2017 fall temperatures were warmer than normal (Figure 4). Based on this information, we expect that 2018 grasshopper populations will likely be similar to 2017 populations. Predicting grasshopper populations is difficult as there are other factors that can also contribute to their rise and fall. In areas experiencing drought stress, scouting should occur early to ensure that potential outbreaks are not missed. This will allow for early management that will be more effective.

Map of Midwestern states. Map has varying colors of green and blue indicating where first 28 degree Fahrenheit frost occurred.
Figure 3. 2017 South Dakota first 28°F frost map. Courtesy: High Plains Regional Climate Center.

Map of South Dakota. Different colored circles indicate different temperature variations.
Figure 4. Map of 2017 South Dakota fall temperature departure from normal. Courtesy: High Plains Regional Climate Center.

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