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 prairieconeflower [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-quinolinecarboxylic acid (imazaquin); 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid (imazethapyr).
Daniel D. Beran, Roch E. Gaussoin and Robert A. Masters
Jack D. Fry, Roch E. Gaussoin, Dan D. Beran and Robert A. Masters
Field studies were conducted at two sites in Nebraska (NE1 and NE2) and one site in Kansas (KS) in 1994 to determine the influence of selected preemergence herbicides on establishment of seeded `Sharp's Improved' buffalograss [Buchloe dactyloides (Nutt.) Engelm.]. Herbicides were applied within 2 days after seeding. Application of imazethapyr at 0.07 kg·ha-1 usually resulted in buffalograss seedling density, vigor, and foliar cover that were superior to buffalograss stands where other herbicides were applied. Buffalograss response to AC 263,222 at 0.07 kg·ha-1 was variable and appeared to be influenced by level of weed interference. Seedling density and vigor of buffalograss on areas treated with AC 263,222 were the same or less than on nontreated areas at KS and NE2, where weed infestations were low and moderate [5% and 45% weed foliar cover 12 weeks after treatment (WAT) on nontreated areas]. In contrast, buffalograss establishment was similar in AC 263,222- and imazethapyr-treated plots at NE1 where the weed infestation was high (>70% weed foliar cover 12 WAT on nontreated areas). At 12 WAT, weed foliar cover was <25 % at NE1 and <1 % at NE2 where imazethapyr and AC 263,222 were applied. Of all herbicides evaluated, imazethapyr at 0.07 kg·ha-1 was superior for suppressing annual grass and broadleaf weeds with no observable deleterious effects on buffalograss establishment from seed. Chemical names used: ±2-[4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-lH-imidazol-2-yl]-5-methyl-pyridine carboxylic acid (AC 263,222); 2-[4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-lH-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid (imazethapyr); 6-chloro-N,N′-diethyl-l,3,5-triazine-2,4-diamine (simazine).