Use of herbicides to control alligatorweed and restore native plants in managed marshes.
Marsh management is used to improve the quality of wetland habitats for a variety of waterfowl and other waterbirds. However, alien plants, such as alligatorweed (Alternanthera philoxeroides (Mart.) Griseb.), may impact success of marsh management by competing with and displacing important native plants. In managed marshes, we tested effects of application rate (high, medium, and low) and timing (April and July) of two herbicides (triclopyr amine and imazapyr) on controlling alligatorweed and restoring native plants. In the year of treatment, imazapyr controlled alligatorweed better than triclopyr amine when applied in April, but the herbicides were equally effective when applied in July. High application rate of herbicides in April controlled alligatorweed better than the low application rate, but application rates of herbicides in July did not influence control. In the year of treatment, application of triclopyr amine resulted in greater native plant biomass than imazapyr. High application rate of herbicides in April resulted in greater native plant biomass in the year of treatment than low application rate, but native plant biomass did not differ among rates of herbicides applied in July. One year after treatment, the high application rate of herbicides resulted in less alligatorweed than the low application rate, and July applications of either herbicide generally controlled alligatorweed better than April applications. Application of imazapyr in July resulted in greater biomass of native plants one year after treatment than either imazapyr or triclopyr amine applied in April. This study demonstrates that single herbicide applications can be effective at controlling alligatorweed, and that these applications can have immediate and longer-term benefits for restoring native plants to managed marshes.