Volume 20, Number 4. Dec 2002 Note 238
Ecological Restoration Notes
Available with permission from the The University of Wisconsin Press http://www.wisc.edu/wisconsinpress/journals/
Mowing Does Not Increase Effectiveness of Herbicide on Crown Vetch in Tallgrass Prairie (Illinois) Amy J. Symstad, Prairie Restoration Ecologist, Illinois Natural History Survey,
[email protected]; Laurel Temmen, Natural Heritage Resident; and Edward Anderson, Natural Heritage Biologist, Illinois Dept. Of Natural Resources, Lost Mound Field Station, 3159 Crim Drive, Savanna, Illinois 61074, 815/273-3184,
[email protected] Like many introduced species, crown vetch (Coronilla varia)—a perennial legume that has been widely planted in the eastern United States—has escaped cultivation and spread to natural areas. In tallgrass prairie ecosystems, where crown vetch forms dense mats that overtop and smother native vegetation, herbicide application is a commonly recommended control method (Solecki 1997). However, some land managers have suggested that mowing crown vetch prior to chemical treatment could improve herbicide coverage (E. Fuge, personal communication). Since mowing adds time and cost to the control process, we decided to investigate whether this approach actually increases the effectiveness of herbicide treatment. In spring 2001, we established four treatments—mowing and herbicide, herbicide alone, mowing alone, and a control— in five areas containing crown vetch scattered throughout a large sand prairie in northwestern Illinois. Within each of the five areas, we randomly assigned a distinct patch of crown vetch to one of the four treatments, and established two 0.5-m x 1-m monitoring plots in each patch. From May 23 to 25, we measured the maximum height of crown vetch and estimated the cover of all vascular plant species, litter, and bare ground in these plots. During the following week, we mowed two vetch patches in each area to a height of about 4 inches (10 cm) using hand-held, steel-bladed brush-cutters. Approximately two weeks later, after the mowed vegetation had compacted and decomposed somewhat, we sprayed one mowed and one unmowed vetch patch in each area with a 2-percent solution of Garlon 3A™. We used a high-pressure wand sprayer, taking care to apply the herbicide at an equal rate in both treatments. We estimated plant, litter, and bare ground cover and measured crown vetch height in the monitoring plots two more times during the growing season, in late July/early August and late September. We found that the herbicide was very effective at top-killing the crown vetch, whether or not the patch was mowed prior to spraying. Median crown vetch cover for all treatments in May was 90 percent. This decreased to no cover in July and less than 1 percent cover in September for both herbicide treatments, and the proportion of crown vetch cover remaining after treatment was not significantly different between the mowed and unmowed herbicide treatments (Table 1). Moreover, although spring mowing alone significantly reduced the July height of crown vetch, mowing alone did not significantly reduce cover in either July or September or height in September (Table 1). Interestingly, crown vetch cover remained relatively high (40 percent of its pre-treatment level) in one of the plots in the mowing and herbicide treatment, while it was completely top-killed in all plots treated with herbicide alone. Although this may simply be an anomaly, it is possible that the heavy thatch created by mowing protected the crown vetch from the herbicide spray.
Volume 20, Number 4. Dec 2002 Note 238
Ecological Restoration Notes
Available with permission from the The University of Wisconsin Press http://www.wisc.edu/wisconsinpress/journals/
It is unlikely that a single year of treatment will eliminate crown vetch from this prairie, and we will continue to monitor the effectiveness of the different treatments. However, our initial results indicate that the extra time and resources spent on mowing crown vetch before herbicide application do not improve, and may even reduce, the effectiveness of the herbicide. Eliminating this step from the control process will increase the number of infestations that we can treat each year.
Table 1
REFERENCES Fuge, E.L. 2001. Communication in talk at Plants out of Place: Invasive Plant Conference for the Upper Midwest, Eau Claire, Wisconsin, March 1-2, 2001. Solecki, M. 1997. Controlling invasive plants. Pages 251-278 in S. Packard and C.F. Mutel (eds.), The tallgrass restoration handbook. Washington, D.C.: Island Press.
