Establishment of big bluestem and Illinois bundleflower mixtures with imazapic and imazethapyr

Weeds interfere with establishment of native grasses and legumes. A study w as conducted to determine the influence of imazapic(1) [(+/-)-2-[4,5-dihydr o-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecar boxylic acid] and imazethapyr [2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5- oxo-1H-imidazol-2-yl]5-ethyl-3-pyridinecarboxylic acid] on weed control and establishment of 'Pawnee' big bluestem (Andropogon gerardii Vitman var. ge rardii Vitman) and Illinois bundleflower [Desmanthus illinoensis (Michx,) M acMill.] planted in three binary mixtures of 220:110, 165:165, and 110:220 pure live seed (PLS) m(-2). Mixtures were seeded st cropland sites near Cla y Center, Mead, and Lincoln, NE. Imazapic and imazethapyr were applied at 7 0 g a.i. ha(-1) before planted species emerged. Imazapic or imazethapyr did not reduce dry matter yields of annual grass weeds, where herbicides were applied in April 1996 at Mead and Clay Center. Both grass and broadleaf wee ds were controlled at Lincoln, where herbicides were applied in early June 1996, The herbicides usually improved big bluestem yields and total forage yields in 1996 and 1997 at all sites. Illinois bundleflower yields at Linco ln, where imazapic and imazethapyr were applied, were greater than 3.0 Mg h a(-1) in 1996 and 1997. In 1997, Illinois bundleflower did not survive at M ead and yielded less than 0.5 Mg ha(-1) at Clay Center, regardless of weed control treatment or seed mixture. Imazapic and imazethapyr can improve the establishment of big bluestem and Illinois bundleflower mixtures.