Interference between Yellow Starthistle and Pubescent Wheatgrass during Grass Establishment

Abstract

Yellow starthistle (Centaurea solstitialis L.) and pubescent wheatgrass (Thinopyrum intermedium spp. barbulatum (Schur) Barkw. & D.R. Dewey) were seeded and subsequently thinned to 0, 130, 260, and 390 plants/m2 in a factorial arrangement. Aggressivity coefficients indicated that intraspecific interference became stronger than interspecific interference, based on biomass of either pubescent wheatgrass and yellow starthistle, as the density of both species increased in a 1:1 ratio. Pubescent wheatgrass provided 0.5 to 1.3 times as much intraspecific interference, plant for plant, as the interspecific interference caused by yellow starthistle. Yellow starthistle provided from 1.5 to 4.6 times as much intraspecific interference, plant for plant, as the interspecific interference caused by pubescent wheatgrass. Weekly leaf counts showed that intra- and interspecific interference from yellow starthistle was detectable 6 weeks after emergence. Weekly leaf counts showed that intraspecific interference from pubescent wheatgrass was detectable 7 weeks after emergence; interspecific interference from pubescent wheatgrass was not detectable using leaf count comparisons. Soil moisture at a 10 cm depth was correlated to leaf number of pubescent wheatgrass but not with leaf number of yellow starthistle. This may reflect the greater competitive ability of yellow starthistle.