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Late-Season Weed Escape Survey Reveals Discontinued Atrazine Use Associated with Greater Abundance of Broadleaf Weeds
- Ross A. Recker, Paul D. Mitchell, David E. Stoltenberg, Joseph G. Lauer, Vince M. Davis
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- Journal:
- Weed Technology / Volume 29 / Issue 3 / September 2015
- Published online by Cambridge University Press:
- 20 January 2017, pp. 451-463
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Atrazine has been used for control of many weeds, primarily broadleaf weeds, in U.S. corn fields since 1957. Recently, the adoption of glyphosate-resistant corn hybrids have led to glyphosate eclipsing atrazine as the most commonly used herbicide in corn production. However, the evolution and spread of glyphosate-resistant weeds is a major concern. Atrazine use in Wisconsin is prohibited in 102 areas encompassing 0.49 million ha where total chlorinated residues were found in drinking water wells at concentrations > 3 μg L−1. Atrazine has been prohibited in many of those areas for > 10 yr, providing an opportunity to evaluate weed community composition differences due to herbicide regulation. In question, has the abundance of broadleaf weeds increased, coupled with an increased reliance on glyphosate, where atrazine use has been discontinued? To answer this, an online questionnaire was distributed to Wisconsin growers in June and then weeds present in 343 fields in late July through mid-September in 2012 and 2013 were counted. Data were summarized for frequency, uniformity, density, and relative abundance to compare weed community composition in fields with discontinued vs. recent atrazine use. Growers used glyphosate in 70 vs. 54% of fields with discontinued vs. recent atrazine use, respectively (P = 0.021). Moreover, broadleaf weeds were found more frequently, (73 vs. 61%; P = 0.03), they had 50% greater in-field uniformity (P = 0.002), and density was 0.4 vs. 0.19 plants m−2 (i.e., twofold greater; P < 0.0001) in discontinued vs. recent atrazine-use fields. Changes were most evident with troublesome glyphosate-resistant broadleaf weeds such as Amaranthus species and giant ragweed. In conclusion, weed community composition consisted of more broadleaf weeds in fields where atrazine has not been used in the recent decade coupled with greater glyphosate use. These results provide evidence of negative long-term implications for glyphosate resistance where growers increased reliance on glyphosate in place of atrazine.
Does Timing Influence the Utility of Reduced Atrazine Rates for Proactive Resistance Management?
- Ross A. Recker, Joseph G. Lauer, David E. Stoltenberg, Paul D. Mitchell, Vince M. Davis
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- Journal:
- Weed Technology / Volume 29 / Issue 3 / September 2015
- Published online by Cambridge University Press:
- 20 January 2017, pp. 464-471
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Atrazine is an important herbicide for broadleaf weed control in corn. Use rates have declined in many corn production systems due to environmental concerns and the availability of other effective herbicides, especially glyphosate in glyphosate-resistant hybrids. However, using multiple effective herbicide modes of action is ever more important because occurrence of herbicide-resistant weeds is increasing. An experiment to compare application timings of reduced rates of atrazine to benefit resistance management in broadleaf weeds while protecting corn yield was conducted in Wisconsin across four site-years in 2012 and 2013. Herbicide treatments consisted of five atrazine rate and timing combinations and three POST base herbicides: glyphosate, glufosinate, and tembotrione. Metolachlor was applied PRE at 2.1 kg ai ha−1 for grass control in all treatments. A linear regression model estimated that atrazine rates ≥ 1.0 kg ai ha−1 applied PRE would prevent exposure of common lambsquarters plants to POST herbicides, but giant ragweed and velvetleaf exposure was not influenced by timing. Corn yield was also not influenced by atrazine rate and timing combinations at the α = 0.05 level; however, at P = 0.06, corn yield was greater for atrazine applied PRE at 1.1 kg ha−1 than for atrazine applied PRE at 0.5 kg ha−1, POST at 1.1 kg ha−1, or not at all. In summary, higher rates of atrazine applied PRE may improve yield, as reported by others, but this study concludes reduced rates of atrazine (i.e., ≤ 1.1 kg ha−1) applied to corn in a POST tank mixture combination provided more consistent control of giant ragweed, velvetleaf, and common lambsquarters compared with atrazine applied PRE. This information should help direct atrazine application timing applied POST when applied at low rates to improve proactive herbicide resistance management.
Effect of Weed Management Strategy and Row Width on Nitrous Oxide Emissions in Soybean
- Rebecca R. Bailey, Thomas R. Butts, Joseph G. Lauer, Carrie A. M. Laboski, Christopher J. Kucharik, Vince M. Davis
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- Journal:
- Weed Science / Volume 63 / Issue 4 / December 2015
- Published online by Cambridge University Press:
- 20 January 2017, pp. 962-971
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Nitrous oxide (N2O) is a potent greenhouse gas with implication for climate change. Agriculture accounts for 10% of all greenhouse gas emissions in the United States, but 75% of the country's N2O emissions. In the absence of PRE herbicides, weeds compete with soybean for available soil moisture and inorganic N, and may reduce N2O emissions relative to a weed-free environment. However, after weeds are killed with a POST herbicide, the dead weed residues may stimulate N2O emissions by increasing soil moisture and supplying carbon and nitrogen to microbial denitrifiers. Wider soybean rows often have more weed biomass, and as a result, row width may further impact how weeds influence N2O emissions. To determine this relationship, field studies were conducted in 2013 and 2014 in Arlington, WI. A two-by-two factorial treatment structure of weed management (PRE + POST vs. POST-only) and row width (38 or 76 cm) was arranged in a randomized complete block design with four replications. N2O fluxes were measured from static gas sampling chambers at least weekly starting 2 wk after planting until mid-September, and were compared for the periods before and after weed termination using a repeated measures analysis. N2O fluxes were not influenced by the weed by width interaction or width before termination, after termination, or for the full duration of the study at P ≤ 0.05. Interestingly, we observed that POST-only treatments had lower fluxes on the sampling day immediately prior to POST application (P = 0.0002), but this was the only incidence where weed influenced N2O fluxes, and overall, average fluxes from PRE + POST and POST-only treatments were not different for any period of the study. Soybean yield was not influenced by width (P = 0.6018) or weed by width (P = 0.5825), but yield was 650 kg ha−1 higher in the PRE + POST than POST-only treatments (P = 0.0007). These results indicate that herbicide management strategy does not influence N2O emissions from soybean, and the use of a PRE herbicide prevents soybean yield loss.
Contributors
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- By Joëlle Adrien, M. Y. Agargun, Negar Ahmadi, Imran M. Ahmed, J. Todd Arnedt, Joseph Barbera, Simon Beaulieu-Bonneau, Marie E. Beitinger, Francesco Benedetti, Glenn Berall, Kirk J. Brower, Gregory M. Brown, Kumaraswamy Budur, Daniel P. Cardinali, Deirdre A. Conroy, Sara Dallaspezia, José Manuel de la Fuente, Paolo De Luca, Diana De Ronchi, Antonio Drago, Matthew R. Ebben, Irshaad Ebrahim, Pingfu Feng, Peter B. Fenwick, Lina Fine, Jonathan Adrian Ewing Fleming, Paul A. Fredrickson, Stephany Fulda, Lucile Garma, Roger Godbout, Reut Gruber, J. Allan Hobson, Andrea Iaboni, Anna Ivanenko, Mayumi Kimura, Milton Kramer, Christoph J. Lauer, Remy Luthringer, Luis Fernando Martínez, Sara Matteson-Rusby, Robert W. McCarley, Charles J. Meliska, Harvey Moldofsky, Charles M. Morin, Sricharan Moturi, Marie-Christine Ouellet, James F. Pagel, S. R. Pandi-Perumal, Barbara L. Parry, Timo Partonen, Wilfred R. Pigeon, Thomas Pollmächer, Nathalie Pross, Elliott Richelson, Naomi L. Rogers, Stefan Rupprecht-Mrozek, Philip Saleh, Andreas Schuld, Alessandro Serretti, Colin M. Shapiro, Christopher Michael Sinton, Marcel G. Smits, D. Warren Spence, Jürgen Staedt, Corinne Staner, Luc Staner, Axel Steiger, Deborah Suchecki, Michael J. Thorpy, Inna Voloh, Bradley G. Whitwell, Robert A. Zucker
- Edited by S. R. Pandi-Perumal, Milton Kramer, University of Illinois, Chicago
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- Book:
- Sleep and Mental Illness
- Published online:
- 05 July 2011
- Print publication:
- 01 April 2010, pp ix-xiii
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