TITLE:
Tolerance of Corn (Zea mays L.) to Early and Late Glyphosate Applications
AUTHORS:
Kris J. Mahoney, Robert E. Nurse, Wesley J. Everman, Christy L. Sprague, Peter H. Sikkema
KEYWORDS:
Dose, Injury, Cob Deformity, Yield
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.5 No.18,
August
26,
2014
ABSTRACT: Fifteen field experiments
were conducted from 2009 to 2012 in Ontario, Canada and Michigan, USA to
determine the tolerance of corn (Zea mays L.) to early (spike or 1- to 2-leaf stage) or late (8- or 10-leaf stage)
applications of 900, 1800, 3600, or 7200 g·ae·ha-1 of glyphosate. Postemergence
applications were evaluated for corn injury, cob length and deformity, crop
moisture at harvest, and yield in the absence of weed competition. In the early
application experiment, no visible injury was detected with applications of up
to 3600 g·ae·ha-1; however, 1.4% injury was observed 4 weeks after
treatment (WAT) when 7200 g·ae·ha-1 was applied to 1- to 2-leaf
stage corn. Yet by harvest, the observed injury was transient as yields were
similar to the untreated control regardless of glyphosate dose or timing. In
the late application experiment, visible injury tended to increase with
glyphosate dose. In addition, for corn treated with 7200 g·ae·ha-1 at the 10-leaf stage, injury increased over time as 6%, 11%, and 12% injury was
observed 1, 2, and 4 WAT, respectively. Similar to the visible injury of
vegetative tissue, cob deformity and reductions in yield tended to increase
with glyphosate dose, but this response varied and the data were pooled into
two environment groups. For example, in one environment group, corn treated
with 7200 g·ae·ha-1 at the 8- and 10-leaf stage had a 9.5% and 14.6%
reduction in yield, respectively. Whereas in another environment group, corn
yields were similar to the untreated control regardless of glyphosate dose or timing.
This research demonstrated that commercially available corn hybrids have tolerance
to glyphosate at doses greater than what has been previously published or could
reasonably be expected during spray overlaps in a field.