Darbyshire, S. J., Francis, A., Crompton, C. W. and Swanton, C. J. 2011. The Biology of Canadian Weeds. 145. Muhlenbergia frondosa (Poir.) Fernald. Can. J. Plant Sci. 91: 205-219. Muhlenbergia frondosa is a perennial grass native to eastern North America, which naturally inhabits moist to wet forest margins and openings, freshwater littoral habitats, and grasslands. In Canada, its spread as a weed appears to have coincided with changes in cultivation practices during the past few decades. Infestations in such crops as maize and soya bean have been reported mainly from southern Ontario and Quebec, and the Midwest and northeastern areas of the United States, where it reduces yields and can be difficult to control. It is shade tolerant and able to compete under the closed canopy of crops. Although this weed can be controlled by herbicides, its ability to spread by regrowth from rhizomes, and its abundant seed production, cause ongoing problems in arable fields, particularly in conservation-tillage systems. As a warm-season C₄ grass, growth begins relatively late in the season (early June in Canada), after most intensive weed control measures have already been taken. Timing herbicide application with active growth stages (10-30 cm) is most effective and the use of herbicide-tolerant crops provides additional control opportunities after crop planting.