2018 Eastern South Dakota Grasshopper Forecast Back »

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


In 2017, researchers at South Dakota State University completed a grasshopper survey of Eastern South Dakota. The last grasshopper survey to be conducted in Eastern South Dakota was published in 1925. As we know, 2017 was an interesting growing season with areas of South Dakota experiencing severe drought conditions. In some of these areas, we found that grasshopper populations were causing defoliation injury to already drought-stressed crops. Factors that can lead to increased grasshopper populations include long, warm falls, decreased ground cover, and limited spring rainfall.

2017 Populations

Leading up to 2017, we experienced several warm falls where the first frost date occurred much later than normal. These conditions allowed grasshoppers to successfully lay eggs for a much longer period of time and were likely part of the reason why we saw increased grasshopper populations in the eastern half of the state.

Areas of South Dakota with grasshopper populations that reached or exceeded the threshold of eight or more grasshoppers per square yard included: Hyde, Hand, Beadle, Kingsbury, Spink, Buffalo, Jerauld, Brule, Aurora, Douglas and Hutchinson counties. In addition, there were several other counties that had multiple samples near threshold levels (Figure 1).

Image of South Dakota with green areas indicating forested area and dark red colors indicating reservation land. There are green triangles representing areas with low grasshopper populations, orange squares representing medium grasshopper populations, and red circles representing grasshopper populations that exceeded thresholds.
Figure 1. Map of 2017 grasshopper abundance for Eastern South Dakota. Green triangles indicate grasshopper populations that were below threshold, orange squares represent grasshopper populations that were approaching threshold, and red circles indicate grasshopper populations that exceeded the threshold. Courtesy: Erica Anderson.
 

2018 Growing Season

One factor that may lead to reduced grasshopper populations in 2018 was the very cool spring we had in 2017. As a result, many of the grasshoppers that we observed were several weeks behind in growth. For most of South Dakota, the first 28°F frost occurred between the first and third weeks of October (Figure 2). This would have given the grasshoppers plenty of time to finish development and lay eggs. Like the previous years, most of South Dakota was warmer than average during the fall (Figure 3). However, trying to predict insect populations is difficult as many additional factors can contribute to their winter survival and overall spring populations. Our recommendation is to scout for spring grasshopper populations, as they will be the first indicator of potential problem areas. Depending on the 2018 growing season, areas with limited rainfall or drought conditions may experience increased grasshopper populations.

Map of Midwestern states. Map has varying colors of green and blue indicating where first 28 degree Fahrenheit frost occurred.
Figure 2. 2017 South Dakota first 28°F frost map. Courtesy: Laura Edwards.
 

Map of South Dakota with different colored dots indicating where temperatures were above or below the normal fall temperature.
Figure 3. Fall 2017 South Dakota departure from normal temperature map. Courtesy: Laura Edwards.

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