Eleven field trials were conducted over a three-year period (2006-2008) at three locations in southwestern Ontario, Canada to evaluate the effect of various weed management strategies in glyphosate-tolerant corn on weed control, crop injury, corn yield, environmental impact and profit margin. No visible injury resulted from the herbicide treatments evaluated. Overall, the effect of all factors assessed were location specific. By 56 days after treatment, depending on location, glyphosate applied at the 7 - 8 leaf stage (LPOST), preemergence (PRE) herbicides followed by ( fb ) glyphosate LPOST and sequential glyphosate applications (EPOST (3 - 4 leaf stage) followed by LPOST) provided more consistent control of annual broadleaf weeds and annual grasses compared to glyphosate applied alone EPOST. Weed control at 56 days after treatment was lower when glyphosate was applied alone LPOST compared to sequential applications of glyphosate or PRE herbicides fb glyphosate. There were no differences in corn yield among the sequential programs evaluated; however, a yield benefit was found when a sequential program was used compared to glyphosate applied alone LPOST. Among the sequential programs the lowest environmental impact was isoxaflutole/atrazine fb glyphosate. The lowest profit margins were associated with atrazine, S-metolachlor/atrazine/benoxacor, dicamba/atrazine and glyphosate LPOST treatments compared to all other treatments. Overall, profit margins tended to be somewhat higher for treatments that included glyphosate applications. Based on these results, the most efficacious and profitable weed management program in corn was a sequential application of glyphosate; however, isoxaflutole/atrazine fb glyphosate was the treatment with the lowest environmental risk while also adding glyphosate stewardship benefits.
G. R. Armel, H. P. Wilson, R. J. Richardson and T. E. Hines, “Mesotrione, Acetochlor, and Atrazine for Weed Management in Corn (Zea mays),” Weed Technology, Vol. 17, No. 2, 2003, pp. 284-290. doi:10.1614/0890-037X(2003)017[0284:MAAAFW]2.0.CO;2
B. G. Young, “Changes in Herbicide Use Patterns and Production Practices Resulting from Glyphosate-Resistant Crops,” Weed Technology, Vol. 20, No. 2, 2006, pp. 301-307. doi:10.1614/WT-04-189.1
G. R. W. Nice, F. Whitford, B. Johnson and C. Janssen, “Assessing the Impact of Educating Growers about Proper Use of Atrazine in Pesticide Applicator Recertification Programs,” Weed Technology, Vol. 22, No. 2, 2008, pp. 326-330. doi:10.1614/WT-07-146.1
C. J. Swanton, R. H. Gulden and K. Chandler, “A Rationale for Atrazine Stewardship in Corn,” Weed Science, Vol. 55, No. 1, 2007, pp. 75-81. doi:10.1614/WS-06-104.1
J. W. Barnes and L. R. Oliver, “Cloransulam Antagonizes Annual Grass Control with Aryloxyphenoxypropionate Graminicides but Not Cyclohexanediones,” Weed Technology, Vol. 18, 2004, pp. 763-772. doi:10.1614/WT-03-181R
R. E. Nurse, C. J. Swanton., F. J. Tardif and P. H. Sikkema, “Weed Control and Yield Are Improved When Glyphosate Is Preceded by a Residual Herbicide in Glyphosate-Tolerant Maize (Zea mays),” Crop Protection, Vol. 25, No. 11, 2006, pp. 1174-1179. doi:10.1016/j.cropro.2006.02.015
C. L. Stewart, R. E. Nurse, A. S. Hamill and P. H. Sikkema, “Precipitation Influences Pre- and Post-Emergence Herbicide Efficacy in Corn,” American Journal of Plant Science, Vol. 3, No. 9, 2012, pp. 1193-1204. doi:10.4236/ajps.2012.39145
S. O. Duke, “Taking Stock of Herbicide-Resistant Crops Ten Years after Introduction,” Pest Management Science, Vol. 61, No. 3, 2005, pp. 211-218. doi:10.1002/ps.1024
I. Heap, “The International Survey of Herbicide Resistant Weeds,” 2012. http://www.weedscience.org
R. E. Jones and R. W. Medd, “Economic Thresholds and the Case for Longer Term Approaches to Population Management of Weeds,” Weed Technology, Vol. 14, No. 2, 2000, pp. 337-350. doi:10.1614/0890-037X(2000)014[0337:ETATCF]2.0.CO;2
J. A. Bond and J. L. Griffin, “Weed Control in Corn (Zea mays) with an Imazethapyr Plus Imazapyr Prepackaged Mixture,” Weed Technology, Vol. 19, No. 4, 2005, pp. 992-998. doi:10.1614/WT-04-267R1.1
B. C. Johnson, B. G. Young and J. L. Matthews, “Effect of Postemergence Application Rate and Timing of Mesotrione on Corn (Zea mays) Response and Weed Control,” Weed Technology, Vol. 16, No. 2, 2002, pp. 414-420. doi:10.1614/0890-037X(2002)016[0414:EOPARA]2.0.CO;2
C. L. Stewart, R. E. Nurse, A. S. Hamill and P. H. Sikkema, “Environment and Soil Conditions Influence Pre- and Post-Emergence Herbicide Efficacy in Soybean,” Weed Technology, Vol. 24, No. 3, 2010, pp. 234-243. doi:10.1614/WT-09-009.1
C. J. Swanton, A. Shrestha, K. Chandler and W. Deen, “An Economic Assessment of Weed Control Strategies in No-Till Glyphosate-Resistant Soybean (Glycine max),” Weed Technology, Vol. 14, No. 4, 2000, pp. 755-763. doi:10.1614/0890-037X(2000)014[0755:AEAOWC]2.0.CO;2
B. Hartzler, “Is one-pass weed control a realistic goal?” Department of Agronomy, Iowa State University Extension Agronomy, 1996, 3pp. Accessed April 8, 2012.
S. A. Gower, M. M. Loux, J. Cardina and S. K. Harrison, “Effect of Planting Date, Residual Herbicide, and Post- Emergence Application Timing on Weed Control and Grain Yield in Glyphosate-Tolerant Corn (Zea mays),” Weed Technology, Vol. 16, No. 3, 2002, pp. 488-494. doi:10.1614/0890-037X(2002)016[0488:EOPDRH]2.0.CO;2
M. M. Loux, A. F. Dobbels, W. G. Johnson, G. R.W Nice, T. T Bauman and J. M. Stachler, “Weed Control Guide for Ohio and Indiana,” Ohio State University Extension Bulletin 789/Purdue Extension Pub No. WS16, 2008, 201 p.
S. A. Payne and L. R. Oliver, “Weed Control Programs in Drilled Glyphosate-Resistant Soybean,” Weed Technology, Vol. 14, No. 2, 2000, pp. 413-422. doi:10.1614/0890-037X(2000)014[0413:WCPIDG]2.0.CO;2
J. L. Corbett, S. D. Askew, W. E. Thomas and J. W. Wil- cut, “Weed Efficacy Evaluations for Bromoxynil, Glufosinate, Glyphosate, Pyrithiobac, and Sulfosate,” Weed Technology, Vol. 18, No. 2, 2004, pp. 443-453. doi:10.1614/WT-03-139R
L. C. Gonzini, S. E. Hart and L. M. Wax, “Herbicide Combinations for Weed Management in Glyphosate-Resistant Soybean (Glycine max),” Weed Technology, Vol. 13, No. 2, 1999, pp. 354-360.
R. E. Nurse, A. S. Hamill, C. J. Swanton, F. J. Tardif, W. Deen and P. H. Sikkema, “Is the Application of a Residual Herbicide Required Prior to Glyphosate Application in No-Till Glyphosate-Tolerant Soybean (Glycine max)?” Crop Protection, Vol. 26, No. 4, 2007, pp. 484-489. doi:10.1016/j.cropro.2006.04.018
L. E. Steckel, C. L. Sprague and A. G. Hager, “Common Waterhemp (Amaranthus rudis) Control in Corn (Zea mays) with Single Preemergence and Sequential Applications of Residual Herbicides,” Weed Technology, Vol. 16, No. 4, 2002, pp. 755-761. doi:10.1614/0890-037X(2002)016[0755:CWARCI]2.0.CO;2
J. Kovach, C. Petzoldt, J. Degni And J. Tette, “A Method to Measure the Environmental Impact of Pesticides,” New York’s Food and Life Sciences Bulletins, Vol. 139, 1992, pp. 139-146.
J. Kovach, C. Petzoldt, J. Degni and J. Tette, “A Method to Measure the Environmental Impact of Pesticides,” 2012. http://www.nysipm.cornell.edu/publications/eiq/
J. Fernandez-Cornejo, “Environmental and Economic Consequences of Technology Adoption: IPM in Viticulture,” Agricultural Economics, Vol. 18, No. 2, 1998, pp. 145-155. doi:10.1016/S0169-5150(97)00054-6
G. Edwards-Jones and O. Howells, “The Origin and Hazard of Inputs to Crop Protection in Organic Farming Systems: Are They Sustainable?” Agricultural Systems, Vol. 67, 2001, pp. 31-47. doi:10.1016/S0308-521X(00)00045-7
C. R. Ziegler, D. W. Donahue, F. A. Drummond and S. N. Smith, “The Ecological Economics of Insecticide Use Associated with the Maine Potato Industry Based on a Producer Survey,” American Journal of Alternative Agriculture, Vol. 17, No. 4, 2002, pp. 159-166. doi:10.1079/AJAA2002159
P. R. Bradley, W. G. Johnson, S. E. Hart, M. L. Buesinger and R. E. Massey, “Economics of Weed Management in Glufosinate-Resistant Corn (Zea mays L.),” Weed Technology, Vol. 14, No. 3, 2000, pp. 495-501. doi:10.1614/0890-037X(2000)014[0495:EOWMIG]2.0.CO;2
W. G. Johnson, P. R. Bradley, S. E. Hart, M. L. Bue-singer and R. E. Massey, “Efficacy and Economics of Weed Management in Glyphosate-Resistant Corn (Zea mays),” Weed Technology, Vol. 14, No. 1, 2000, pp. 57- 65. doi:10.1614/0890-037X(2000)014[0057:EAEOWM]2.0.CO;2
L. P. Gianessi, “Economic and Herbicide Use Impacts of Glyphosate-Resistant Crops,” Pest Management Science, Vol. 61, No. 3, 2005, pp. 241-245. doi:10.1002/ps.1013
J. A. Ferrell and W. W. Witt, “Comparison of Glyphosate with Other Herbicides for Weed Control in Corn (Zea mays): Efficacy and Economics,” Weed Technology, Vol. 16, No. 4, 2002, pp. 701-706. doi:10.1614/0890-037X(2002)016[0701:COGWOH]2.0.CO;2
Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), “Guide to Weed Control, Publication 75,” Toronto, 2008, 379 p.