Agricultural Sciences, 2014, 5, 1007-1014 Published Online September 2014 in SciRes. http://www.scirp.org/journal/as http://dx.doi.org/10.4236/as.2014.511109 How to cite this paper: Mahoney, K.J., Nurse, R.E. and Sikkema, P.H. (2014) Tolerance of Maize (Zea mays L.) and Soybean [Glycine max (L.) Merr.] to Late Applications of Postemergence Herbicides. Agricultural Sciences, 5, 1007-1014. http://dx.doi.org/10.4236/as.2014.511109 Tolerance of Maize (Zea mays L.) and Soybean [Glycine max (L.) Merr.] to Late Applications of Postemergence Herbicides Kris J. Mahoney 1* , Robert E. Nurse 2 , Peter H. Sikkema 1 1 University of Guelph, Ridgetown Campus, Ridgetown, Canada 2 Agriculture and Agri-Food Canada, Harrow, Canada Email: * kmahoney@uoguelph.ca Received 12 July 2014; revised 22 August 2014; accepted 20 September 2014 Copyright © 2014 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract Seven maize (Zea mays L.) and three soybean [Glycine max (L.) Merr.] field experiments were con- ducted from 2006 to 2009 at various locations in southern Ontario, Canada to determine the to- lerance of these crops to late applications of the maximum labeled herbicide dose. Single and se- quential (simulating a spray overlap) applications were evaluated for visible injury, plant height, and crop yield in the absence of weed competition. Maize exhibited excellent tolerance to herbi- cides applied at the 9- to 10-leaf growth stage as visible injury levels for almost all tested herbi- cides was similar to the untreated control 7 days after treatment (DAT). However, the sequential application of dicamba/diflufenzopyr or foramsulfuron caused 6 and 8% injury 7 DAT and 8 and 14% reduction in maize height 28 DAT, respectively. The observed injury and stunting were tran- sient as there were no differences in yield at harvest. Soybean displayed good tolerance to most herbicides applied at the 7 th trifoliate leaf growth stage as visible injury levels were similar to the untreated control. However, thifensulfuron-methyl was injurious regardless of application and imazethapyr was injurious with sequential applications. For example, single thifensulfuron-me- thyl, sequential thifensulfuron-methyl, and sequential imazethapyr application treatments caused 35, 48, and 25% injury 7 DAT, respectively. Sequential thifensulfuron-methyl treatments also caused a 28 and 17% reduction in soybean height 14 and 28 DAT, respectively. Visual injury con- tinued to be detected up to 56 DAT for single thifensulfuron-methyl, sequential thifensulfuron- methyl, and sequential imazethapyr treatments. But, soybean yields were reduced by 10% for on- ly sequential thifensulfuron-methyl application treatments. For all other herbicides tested, the yields at harvest were similar to the untreated control. This research demonstrated that maize had exceptional tolerance to all the herbicides used in this study whereas soybean was tolerant to most of the herbicides used in this study. * Corresponding author.