TITLE:
Control of Glyphosate-Resistant Giant Ragweed (Ambrosia trifida L.) with Isoxaflutole and Metribuzin Tankmix
AUTHORS:
Scott Ditschun, Nader Soltani, Darren E. Robinson, François J. Tardif, Allan C. Kaastra, Peter H. Sikkema
KEYWORDS:
Additive, Antagonistic, Giant Ragweed, Glyphosate, Herbicide Resistance, Soybean, Synergistic, Yield
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.7 No.6,
April
27,
2016
ABSTRACT: Five field trials were conducted over a two-year period (2013, 2014) to
determine the control of glyphosate-resistant (GR) giant ragweed with isoxaflutole
(IFT) and metribuzin (MTZ) applied alone and in combination. Treatments were
designed to assess the dose response of an IFT plus MTZ tank-mix as well as
each chemical applied alone to classify the response using Flint’s adaptation
of Colby’s equation. Two factor factorial experiments were performed in the
growth room to ascertain the response of IFT versus glyphosate, IFT versus MTZ,
and IFT plus MTZ versus glyphosate on single plants. Field experiments
evaluated the control of GR giant ragweed with IFT plus MTZ in tank-mix in a
1:4 ratio. The rate of IFT plus MTZ for 80% control of GR giant ragweed at 4
and 8 weeks after application (WAA) was 518 (104 g a.i. ha-1 IFT +
414 g a.i. ha-1 MTZ) and 631 g a.i. ha-1 (126 g a.i. ha-1 IFT + 505 g a.i. ha-1 MTZ), respectively. A rate of 668 and 467 g
a.i. ha-1 was required to reduce GR giant ragweed density and
biomass by 80%, respectively. Field experiments evaluating the control of GR
giant ragweed with tank-mixes of IFT plus MTZ, where glyphosate was a constant
tank-mix partner, were mostly synergistic. However, the low tank-mix rate (52.5
+ 210 g a.i. ha-1) had an additive response for GR giant ragweed
biomass reduction. When tested in the greenhouse and growth room, glyphosate
susceptible (GS) giant ragweed showed some antagonism with glyphosate and
isoxaflutole tank-mixes at rates less than commercial field rates. GR giant
ragweed showed an additive response across all treatments in the growth room.
Greenhouse experiments evaluating IFT versus MTZ and IFT plus MTZ versus
glyphosate revealed all tank-mix treatments to be synergistic at 2 WAA.