A Comparison of Phragmites australis Control Measures in Wisconsin Coastal Wetlands

The common reed, Phragmites australis, is a highly aggressive species that outcompetes native species on shorelines, wetlands and roadways across the Great Lakes Basin. Prior to my analysis glyphosate and imazapyr (Habitat 7) herbicides were applied to more than 600 acres at selected sites along the west shore of lower Green Bay. I explored alternative secondary control treatments for increasing the effectiveness of the aerial herbicide treatment. Sample plots were evaluated in 4 treatment categories: 1) herbicide 2) herbicide + burning, 3) herbicide + mowing, and 4) control (no treatment). Measurements within plots included percent cover of P. australis and all other plant species, average litter depth, and average height of P. australis. Results suggest that local eradication of P. australis is difficult, if not impossible, with one set of treatments. Treatment of P. australis, however, is the first step in restoring native wetlands to preinvasion condition. Percent cover of native wetland species was much higher at treated plots compared with untreated plots. Certain native plant species can rather quickly repopulate treated wetlands after treatment. In this study, native species were found in untreated control plots, but the low species abundance and poor condition of plants in these plots suggests that time might be critical to the treatment of Phragmites stands. Native wetland plants probably will not persist for many years after P. australis invasion. I conclude that application of a secondary treatment of mowing or burning after herbicide application increases the success of Phragmites control and improves the ability of native species to re-establish populations in Great Lakes coastal wetlands.