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 can interfere with the establishment of legumes and increase probability of stand failure. Four experiments were conducted from 1994 to 1997 to determine 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)-5-oxo-1H-imidazol-2-yl]5-methyl-3-pyr idinecarboxylic acid] applied preemergence at 70 g a.i. ha^-1 could reduce weed interference and improve establishment of seeded grassland legumes. Six native legumes and one introduced legume, crownvetch (Coronilla varia L.), were planted into prepared seedbeds at sites near Mead, NE. Legume response to the herbicides varied among species and sites. Crownvetch, partridgepea [Chamaecrista fasciculata (Michx.) Greene; syn. Cassia chamaecrista L.), and purple prairieclover (Dalea purpurea Vent.) exhibited tolerance to both imazethapyr and imazapic in most experiments and their establishment, as indicated by stem density and/or forage yield collected 14 mo after planting, was improved when treated with the herbicides in weedy environments. Imazapic treatment injured leadplant (Amorpha canescens Pursh), Canada tickclover [Desmodium canadense (L.) DC.], and roundhead lespedeza (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 reduce weed interference and improve the establishment of certain grassland legumes.