Investigators: Joanne Whalen - Extension IPM Specialist
Marty Spellman - Extension IPM Associate
Kimberly Tarburton - Summer Assistant - collected data and wrote report
Cooperators: William Parker
William Jester/Frank Hrupsa
W. Darwin Cates/Franklin Hanson
C. Delbert Cain and Michael Cain
Roger Bullock
Buffer strips are small areas or strips of land in permanent vegetation designed to intercept pollutants, enhance wildlife habitat, and protect biodiversity among other environmental concerns (NRCS). A concern has been raised that these buffer strips may cause an increase of grasshopper damage in field crops. In order to better understand this issue, the following aspects of buffer strips and grasshopper populations were studied: (1) buffer strip composition, (2) species of grasshoppers present in buffer strips and fields and (3) population size of grasshoppers.
In southwest Kent County, six buffer strips and associated fields plus five fields not associated with buffer strips were used in this study. Emergence cages were set up in mid-April in the buffer strips. These were checked from April to the beginning of June for emerging long horn and short horn grasshoppers. Also starting in April, buffer strips were checked for grasshoppers by taking ten samples with a sweep net along the strip. Long horn and short horn grasshopper counts were kept separate.
Field sampling for grasshoppers began in June. In soybean fields with buffer strips, the sampling pattern was ten sweeps in five locations with two of the spots being next to the buffer strip (5-25 yards), two of the spots into the field away from the buffer strip (80-100 yards) and a final spot further into the field (150-175 yards). The number of grasshoppers was recorded. In field corn with buffer strips the sampling pattern was ten plants in a row in 5 spots in the same positions as the soybean fields. Here the number of damaged plants was recorded.
Comparison fields that did not have buffer strips along its edges were found for each site. Characteristics such as tillage, planting date, and proximity to one another were taken into account and an effort was made to match up fields with similar characteristics. Comparison fields were sampled by taking ten sweeps in five random spots in the field for soybeans and examining corn ten corn plants in five random spots. Sampling was completed by mid-August.
For two consecutive weeks in July the number of damaged plants out of ten was noted in soybean fields in the same locations as sweeping.
Collection of grasshoppers was also done weekly. Grasshoppers were collected into plastic bags and labeled with the grower’s name, date and location. Grasshoppers were collected from buffer strips, adjacent fields and comparison fields. They were then killed by freezing and pinned in order to identify to species using the online Bulletin No. 584S from Colorado State University.
Emergence cages set up in the buffer strips did not provide any relevant information. Low numbers of grasshoppers were found in the cages. Sweeping of the buffer strip showed a population of long horns developing early in the season that began to die back down around the end of June. Long horns were generally only found in the buffer strip through out the season, and they appear to pose no economic threat. Short horns were not present until the middle of May. Populations increased significantly by mid-June and then declined by early August (Figure 1).
Sampling in different locations within the field relative to the buffer strip was done in hopes of discovering a general movement of the grasshoppers. However, this was not the case. No patterns in the data relating to the location of the grasshopper within the field were found. Numbers varied in time and space through out the season. Grasshopper nymphs were found on the interior of the field (80-100 yards and 150-175 yards) on the very first day of sampling. No correlation was found when the buffer strip grasshopper data was superimposed on the grasshopper field data. This indicates that grasshoppers are emerging throughout the field as well as in the buffer strips and that there seems to be no net movement of grasshoppers from the buffer strip into the fields. Sampling data from the corn fields were left out of all comparisons with the soybean fields because of different methods of determining grasshopper presence. Data in the corn fields was also variable and showed no trends.
The overall population of grasshoppers in the fields was significantly lower than numbers in the buffer strips (Figure 2). This raises the question of whether the buffer strips keep grasshoppers out of the field or do they provide a place for grasshoppers to increase in number resulting in greater pest pressure in the field? Further research needs to be done in order to answer this question.
Some clues are given to start answering this question, however, when comparing the number of grasshoppers found in fields with and without buffer strips. In three out of the five soybean locations, there were more grasshoppers in the fields with buffer strips than in those without buffer strips (Figures 3, 4 & 7). In one of the locations there were many more grasshoppers in the field without the buffer strip than its counterpart with the strip (Figure 5). In the remaining location, numbers varied depending on the date, giving generally the same amount of grasshoppers in each type of field (Figure 6). Factors such as tillage and weed presence seemed to influence the presence of grasshoppers in these fields as well, indicating that there is more involved in the presence of grasshopper populations than whether or not they have buffer strips. It should also be noted that the economic threshold of one grasshopper per sweep was never reached in any of the fields. In the corn location, there was more grasshopper damage in the field with a buffer strip. However, populations remained high only along the edge of the field.
The number of damaged plants in soybean fields was noted for a short time in response to the problem of grasshoppers being present in a field, but counts not being accurately reflected in sweep net samples. However, this data was only collected for two weeks since it accounted for total damage for multiple pests and did not accurately reflect what was happening with current grasshopper populations. The problem of grasshoppers avoiding the sweep net is still an issue that should be addressed in future studies.
The use of insecticides and other control methods for the grasshoppers by growers during the study must also be noted. For grower A, the main soybean field was sprayed with Lorsban on July 9, 2002 , along with the mowing of the adjacent buffer strip the week before. Grower B sprayed dimethoate June 19, 2002 on the main soybean field.
Grasshoppers found in the soybean fields and buffer strips consisted of mainly three species. The first adult collected was the redlegged grasshopper (Melanoplus femurrebrum) around the end of June. Next, the Carolina grasshopper or dust grasshopper (Dissosteira Carolina) was collected in early to mid July. The differential grasshopper, Melanoplus differentialis, was the last one to be collected in late July, early August. Common to all three species are their wide geographical range, diet variety, and strong powers of flight. The redlegged grasshopper and the differential grasshopper are considered significant crop pests, while the Carolina grasshopper is only a minor pest. The differential grasshopper seems to prefer grasses such as small grains and corn, but still attacks other crops. All three species were found in both buffer strips and in the fields.
The answer to the question, do buffer strips contribute to an increase in grasshopper problems in field crops, needs further investigation. Although there was a slight trend for more grasshoppers in fields with buffer strips, economic damage did not always occur in those fields. The data seems to indicate that grasshoppers may already be present in the many fields with buffer strips resulting in an increase their population. However, buffer strips are not the only source of this increase as can be seen from the comparison field in Figure 5. This study has opened up new avenues for investigation while providing some general information about grasshopper populations and habits in western Kent County.
“Buffer Strips: Common Sense Conservation”. US Department of Agriculture: Natural Resources Conservation Service. Online. www.nrcs.usda.gov/feature/buffers/.
Capinera J. I., and T.S. Sechrist. Grasshoppers (Acrididae) of Colorado: Identification, Biology and Management. Colorado State University Experimental Station; Fort Collins . Bulletin No. 584S. Online 1999. www.sdvc.uwyo.edu/grasshoppers/ghcotoc.htm.
Pfadt, Robert E. Grasshopper Species Fact Sheets. Wyoming Agricultural Experiment Station Bulletin 912. Online. www.sidney.ars.usda.gov/grasshopper/ID_Tools/F_Sheets/index.htm.
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