Agricultural Sciences, 2015, 6, 346-351 Published Online March 2015 in SciRes. http://www.scirp.org/journal/as http://dx.doi.org/10.4236/as.2015.63035 How to cite this paper: Belfry, K.D., Shropshire, C. and Sikkema, P.H. (2015) Evaluation of Delayed Glyphosate Burndown in No-Till Soybean. Agricultural Sciences, 6, 346-351. http://dx.doi.org/10.4236/as.2015.63035 Evaluation of Delayed Glyphosate Burndown in No-Till Soybean Kimberly D. Belfry * , Christy Shropshire, Peter H. Sikkema University of Guelph Ridgetown Campus, Ridgetown, Canada Email: * kimberly.belfry@gmail.com Received 27 February 2015; accepted 15 March 2015; published 20 March 2015 Copyright © 2015 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 Application of a preplant or preemergence glyphosate burndown is routine in most no-tillage production systems of annual crops, however, time of application may influence overall weed control and grain yield. Six field trials were conducted over a three-year period (2008, 2009 and 2010) near Ridgetown, Ontario, Canada to determine the effect of glyphosate burndown applica- tion timing in glyphosate-resistant (GR) no-tillage soybean [Glycine max (L.) Merr.]. Soybean growth was reduced 5%, 10% and 20% when the burndown was delayed to 1, 5 and 12 days after planting (DAP), when evaluated one week after application (WAA), respectively. By 8 WAA, pre- dicted burndown timing increased to 9, 14 and 23 DAP, and was 10, 17 and 26 DAP at 12 WAA, to reduce soybean growth by 5%, 10% and 20%, respectively. Similarly, burndown application at 14, 21 and 30 DAP corresponded to a soybean yield reduction of 5%, 10% and 20%. Seed moisture content was generally insensitive to burndown timing; 80 and 140 DAP were required to increase moisture by 5% and 10%, respectively. This research indicates that delaying glyphosate burn- down by up to 14 DAP, approximately VE to VC growth stage, has the potential to result in a mod- est reduction in soybean yield (5%). Keywords Burndown, Glyphosate, Soybean 1. Introduction With record production of nearly 6 million tonnes in 2014, soybean [Glycine max (L.) Merr.] continues to be Canada’s most popular leguminous field crop [1]. Accounting for more than 60% of total Canadian production, Ontario soybean is valued at approximately 1.5 million dollars and typically occupies greater than 1 million hectares of crop land annually [2]. Soybean production has been met with continued growth over the past two * Corresponding author.