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Western South Dakota Grasshopper Forecast
By: Adam J. Varenhorst, South Dakota State University - 05/18/2018

In South Dakota, there are several species of grasshoppers that can have a negative impact on rangeland health. The U.S. 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.

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 28F frost for most of Western South Dakota didn't occur until the first week of October. 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. In general, the 2017 fall temperatures were warmer than normal.

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.

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