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Daniel D. Beran, Roch E. Gaussoin, and Robert A. Masters

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).

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J. Michael Goatley Jr., Victor L. Maddox, and Robert M. Watkins

Research was conducted over 2 years to evaluate efficacy of various levels and combinations of imazaquin and AC 263,222 for growth regulation of unimproved bahiagrass (`Pensacola') turf. Imazaquin at 0.42 kg·ha–1 caused only slight bahiagrass discoloration in all trials and reduced seedhead count (as compared to the nontreated control) by ≥80% for 8 weeks after treatment (WAT) following a July 1992 application. AC 263,222 at 0.042 or 0.056 kg·ha–1 applied in late May or June provided 100% seedhead control through 8 WAT. However, AC 263,222 applied in July 1992 and Aug. 1993 at 0.056 kg·ha–1 resulted in unacceptable discoloration through 8 WAT. AC 263,222 at 0.014 or 0.028 kg·ha–1 provided ≥90% seedhead control with only minimal discoloration following applications in July or Aug. 1993, indicating that lower rates of AC 263,222 provided acceptable seedhead control of bahiagrass during times when growth was slowed due to moisture stress. Chemical names used: (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid (AC 263,222); 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid (imazaquin).

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Jacqueline K. Burns, Ulrich Hartmond, and Walter J. Kender

The abscission action of two sulfonylureas and one imidazolinone was evaluated in laboratory studies with harvested orange (Citrus sinensis L. cv. Valencia) fruit and greenhouse studies with orange (cv. Hamlin) and grapefruit (Citrus paradisi Macf. cv. Marsh) trees. Dipping harvested fruit in 90 mg·L–1 imazameth, 2 mg·L–1 metsulfuronmethyl, or 30 mg·L–1 prosulfuron solutions increased levels of internal ethylene. Internal ethylene concentration was higher when fruit were dipped in 2 mg·L–1 metsulfuron-methyl solutions at low pH. Fruit retained on trees and dipped in 2 mg·L–1 metsulfuron-methyl solutions produced more ethylene than control fruit. Drop of treated fruit began when ethylene production was at a maximum. High temperatures (average 33 °C) suppressed ethylene production and fruit drop of metsulfuron-methyl–treated fruit. The results indicate the importance of environmental conditions in evaluating the potential of sulfonylureas and imidazolinones as abscission agents for citrus. Chemical names used: ±-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid (imazameth); methyl 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2yl) amino] carbonyl] amino] sulfonyl] benzoate (metsulfuron-methyl); 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl) phenylsulfonyl] urea (prosulfuron); N-(phosphonomethyl) glycine (glyphosate); 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1 H-imidazol-2-yl]-3-quinolinecarboxylic acid (imazaquin).

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M. Lenny Wells and Eric P. Prostko

.27 meq/100 g. The 2009 orchard, situated on Tifton loamy sand, has 8% clay and a CEC of 10.48 meq/100 g. Imidazolinone herbicide adsorption and hysteresis can more readily occur with increasing clay content and CEC ( Barnes et al., 1989 ; Goetz et al

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Marcus A. Jones, Nick E. Christians, Daniel Weisenberger, and Zachary J. Reicher

Weed Technol. 18 977 981 Malefyt, T. Quakenbush, L. 1991 Influence of environmental factors on the biological activity of the imidazolinone herbicides 103 127 Shaner D.L. O'Conner S.L. The

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Kalpana K.C. Adhikari, Mary Ruth McDonald, and Bruce D. Gossen

included three canola cultivars from Pioneer Hi-Bred, Ontario, Canada: ‘46A76 IMI’ (imidazolinone-tolerant), ‘46A65’ (conventional), and ‘45H21 RR’ (Roundup Ready hybrid), and one from Bayer Crop Science, Ontario, Canada: ‘Invigor 5020 LL’ (Liberty Link

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Hiroko Sato, Tadashi Takamizo, Tsutomu Shimizu, Kiyoshi Kawai, and Koichiro Kaku

). It is the target of at least five structurally distinct classes of herbicides, including pyrimidinylcarboxylates, sulfonylureas, imidazolinones, triazolopyrimidine sulfonamides, and sulfonylaminocarbonyltriazolinones ( Shimizu et al., 2002 ). ALS

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Lyn A. Gettys and William T. Haller

labeled for postemergence weed control in aquatic and terrestrial systems. It is an imidazole derivative in the imidazolinone class of herbicides and is also referred to as the ammonium salt of imazamox ( Kegley et al., 2008 ). Imazamox inhibits the

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Jialin Yu and Nathan S. Boyd

, J.A. 2001 Acetolactate synthase-inhibiting herbicides on imidazolinone-tolerant rice Weed Sci. 49 652 657 Wiedman, S.J. Appleby, A.P. 1972 Plant growth stimulation by sublethal concentrations of herbicides Weed Res. 12 65 74

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Genhua Niu, Denise S. Rodriguez, and Cynthia McKenney

among the selected species. Literature Cited Beran, D.D. Gaussoin, R.E. Masters, R.A. 1999 Native wildflower establishment with imidazolinone herbicides HortScience 34 283 286 Bretzel, F. Pezzarossa, B. Carrai, C. Malorgio, F. 2009 Wildflowers planting