Japanese stiltgrass, an annual grass species native to eastern Asia, has become a serious invasive-plant problem in the eastern United States. We compared the efficacy of herbicides and nonchemical options found effective for controlling stiltgrass in earlier studies, with organic herbicides and herbicides used at reduced rates in a wooded floodplain along the lower Connecticut River. We compared the effect of 2 yr of conventional and alternative treatments on cover of other nonnative and native species. Four blocks of 18 plots (3 by 4 m [9.8 by 13.1 ft]) were established in May 2008. Treatments included directed heating with a propane torch (June, July), hand-pulling (July), mowing with a string trimmer (July, August), foliar applications of household vinegar [5% acetic acid] (June, July) and the herbicides imazapic (June), pelargonic acid (June, July), and pelargonic acid plus pendimethalin (June). The following herbicides were applied at labeled doses and at one-fourth labeled doses: fenoxaprop-p-ethyl (July), glufosinate (August), and glyphosate (August). Stiltgrass cover and height were evaluated periodically, and plant samples were collected in autumn of 2008 and 2009 to determine the number of viable seeds produced. Final evaluations were conducted in June 2010 after 2 yr of treatment. Stiltgrass cover averaged 88% on untreated plots in fall. All treatments reduced stiltgrass cover and seed production. The least-effective treatments were hand-pulling, pelargonic acid, and vinegar in July. Direct heating, mowing, and vinegar in June reduced seed production by more than 90%. All treatments containing imazapic, pelargonic acid plus pendimethalin, fenoxaprop-p-ethyl, glufosinate, and glyphosate completely prevented stiltgrass seed production in the second year of treatment. Effective control of stiltgrass can be achieved during a 2-yr period with a variety of herbicides, including herbicides at one-fourth of the labeled dose, and through nonchemical treatments.
Nomenclature: Fenoxaprop-p-ethyl; glufosinate; glyphosate; imazapic; pelargonic acid; pendimethalin; Japanese stiltgrass, Microstegium vimineum (Trin.) A. Camus var. imberbe (Nees) Honda.
Management Implications: Japanese stiltgrass, an increasingly common, invasive grass species along riparian and transportation corridors, including hiking trails, can depress native, herbaceous plant populations and alter soil processes. Although earlier studies have shown that several herbicides provide effective control of stiltgrass infestations, many infestations occur in forests where regulations, deeds, or active public opposition can limit herbicide application as a management option. During a 2-yr period, we compared the relative effectiveness of several synthetic herbicides with an “organic” herbicide, acetic acid (household vinegar), and the nonchemical options of hand-pulling, cutting, and directed heating with a propane torch. We also examined the effectiveness of the herbicides fenoxaprop-p-ethyl, glufosinate, and glyphosate at labeled and one-fourth labeled doses. Hand-pulling, pelargonic acid, and vinegar in July were not sufficiently effective to be recommended. Vinegar in June and mowing provided better, but not complete, control. Directed heating and the other herbicides, even at one-fourth doses, provided nearly complete control of stiltgrass. Use of herbicides at low doses might minimize public opposition, provide effective control, and reduce environmental effects. Control of stiltgrass can be achieved without herbicides, but nonchemical methods will require additional time and labor costs.