Smutgrass is an invasive warm-season perennial bunch-type grass native to tropical Asia. The two varieties of smutgrass prevalent in Florida are small smutgrass and giant smutgrass. Laboratory seed germination experiments were conducted on both smutgrass varieties to determine the effect of various environmental factors on germination and emergence. The average germination rate for both varieties was 88% at 30/20 C day/night temperatures. Seed germination for both varieties was greater under simulated temperature flux than at constant temperatures. Seed of both varieties germinated at four simulated Florida temperature fluxes (22/11, 27/15, 33/24, and 29/19 C day/night), although the germination of small smutgrass and giant smutgrass was reduced at 33/24 and 22/11 C, respectively. Germination of small and giant smutgrass under dark conditions was 27 and 53%, respectively. Both smutgrass varieties germinated over a wide range of pH values. Small and giant smutgrass germination was inhibited at water potentials below −0.2 MPa and when small smutgrass seed was placed below the soil surface. Emergence of giant smutgrass seed did not occur below 3 cm. Both smutgrass varieties germinated over a broad range of environmental conditions, indicating their capability of year-round germination; however, germination is only likely to occur under field conditions during the summer growing season when rainfall is prevalent. These results indicate that both species have the ability to germinate over a wide range of environmental conditions but that germination is inhibited by moisture stress and depth of burial. Considering that giant smutgrass prefers higher temperatures than small smutgrass, the advent of rainfall from June through September is conducive for germination. Practices that focus on the germination pattern of smutgrass could lead to better long-term management of smutgrass in Florida.

Smutgrass is an invasive, well-rooted perennial that has long beenrecognized as an aggressive weed throughout Florida and in the subtropicalregions of the United States. Small smutgrass and giant smutgrass are thetwo predominant smutgrass varieties found in Florida. The native soil pH ofFlorida flatwoods is 4.5 to 5.0 which is lower than the level of soil pHrecommended for optimum bahiagrass growth. Therefore, replacement seriesexperiments were conducted in a greenhouse in 2010 and 2011 to compare thecompetitive ability of bahiagrass with each of the two varieties ofsmutgrass at three levels of soil pH (4.5, 5.5, and 6.5), two densities; 4(low) and 8 (high) plants pot−1, and at five planting ratios of100 : 0, 75 : 25, 50 : 50, 25 : 75, and 0 : 100. Relative competitiveability and aggressivity of giant smutgrass was greater than bahiagrassacross all pH levels and densities, whereas relative competitive ability andaggressivity of bahiagrass was greater than small smutgrass in all pH levelsand densities, except at pH 6.5. At pH 5.5, biomass accumulation of giantsmutgrass was at least 73% higher than bahiagrass, whereas small smutgrassbiomass was at least 46% lower than bahiagrass at equal planting ratios ofboth low and high densities. Differential responses were observed onbahiagrass competitive ability with small and giant smutgrass. Amending soilpH is not a likely option to increase the growth and competitive ability ofbahiagrass over giant smutgrass. However, for small smutgrass, it is likelyto increase the aggressivity of bahiagrass in bahiagrass–small smutgrassmixture, unless the soil pH is raised above 5.5.