Grassland legume establishment with imazethapyr and imazapic

Legumes are important components of grassland communities in North America and have potential to improve grassland productivity and diversity. Weeds c an interfere with the establishment of legumes and increase probability of stand failure. Four experiments were conducted from 1994 to 1997 to determi ne if the imidazolinone herbicides imazethapyr [2-[4,5-dihydro-4-methyl-4-( 1-methylethyl)-5-oxo-1H- imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid] and imazapic [(+/-)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-4-oxo-1H-imid azol-2-yl]-5-methyl-3-pyridinecarboxylic acid] applied preemergence at 78 g a.i. ha(-1) could reduce weed interference and improve establishment of se eded grassland legumes. Six native legumes and one introduced legume, crown vetch (Coronilla varia L,) were planted into prepared seedbeds st sites nea r Mead, SE. Legume response to the herbicides varied among species and site s. Crownvetch partridgepea [Chamaecrista fasciculata (Michx.) Greene; syn, Cassia chamaecrista L.), and purple prairieclover (Dalea purpurea Vent.) ex hibited tolerance to both imazethapyr and imazapic in most experiments and their establishment, as indicated by stem density and/or forage yield colle cted 14 mo after planting, tvas improved when treated with the herbicides i n weedy environments. Imazapic treatment injured leadplant (Amorpha canesce ns Pursh), Canada tickclover [Desmodium canadense (L DC.], and roundhead le spedeza (Lespedeza capitata Michx.), resulting In lower stem densities and/ or forage yields than when imazethapyr was applied. Based on these findings , preemergence application of imazethapyr and imazapic can be used to reduc e weed interference and improve the establishment of certain grassland legu mes.