Native wildflower establishment with imidazolinone herbicides

Abstract

Native wildflowers are important components of grassland communities and low-maintenance wildflower seed mixtures. Weed interference limits successful establishment of native wildflowers from seed. Experiments were conducted to determine the influence of the imidazolinone herbicides imazethapyr, imazapic, and imazaquin on the establishment of blackeyed susan (Rudbeckia hirta L.), upright prairiecone flower [Ratibida columnifera (Nutt) Woot. and Standl.], spiked liatris [Liatris spicata (L.) Willd.], blanket flower (Gaillardia aristata Pursh.), purple coneflower [Echinacea purpurea (L.) Moench.], and spotted beebalm (Monarda punctata L.). Wildflower response to the herbicide treatments was variable and appeared to be influenced by the level of weed interference. Establishment of the native wildflowers after application of imazethapyr or imazapic at 70 g·ha-1 a.i. was generally improved at sites with greater weed interference. Emergence and density of wildflowers was often reduced by imazapic in sites with low weed interference. Flower density during the second growing season was usually either improved or not reduced by either imazethapyr or imazapic. Based on these findings, imazethapyr and imazapic can reduce weed interference and improve the establishment of some native wildflowers in areas with high weed infestations. Chemical names used: (±) -2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3 -pyridinecarboxylic acid (imazapic); 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinoline carboxylic acid (imazaquin); 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-p yridinecarboxylic acid (imazethapyr).