10.25394/PGS.11894688.v1
Nicholas Cade Hayden
Nicholas Cade
Hayden
Dicamba Volatilization and the Effect of Synthetic Auxin Herbicides on Sensitive Soybean
Purdue University Graduate School
2020
Dicamba
2,4-D
Soybean
Crop and Pasture Protection (Pests, Diseases and Weeds)
2020-02-26 20:05:28
Thesis
https://hammer.purdue.edu/articles/thesis/Dicamba_Volatilization_and_the_Effect_of_Synthetic_Auxin_Herbicides_on_Sensitive_Soybean/11894688
<p>The broad adoption of soybean resistant
to synthetic auxin herbicides has led to increased risk for off-target exposure
of sensitive plants to these herbicides through both tank-contamination and
drift. New dicamba and 2,4-D formulations have been commercialized in an
attempt to reduce the potential for off-target movement. A great deal of
research has been conducted on soybean response to auxin herbicides alone, but
when other postemergence herbicides are introduced into the equation, the
effects of 2,4-D and dicamba have not been sufficiently studied. Additionally,
the volatilization of dicamba formulations available prior to the registration
of new formulations for use in dicamba-resistant soybean has been characterized
in order to determine factors that influence off-target movement. However, the
volatilization of these new formulations has not been extensively investigated.
</p>
<p> Field
experiments were conducted to determine 1) the response of glyphosate-resistant
soybean to dicamba and 2,4-D, and 2) the influence of a full rate of dicamba
applied with tank-contamination doses of 2,4-D on the response of dicamba/glyphosate-resistant
soybean. Glyphosate-resistant soybean response to 2,4-D and dicamba were
similar to published literature. The ED<sub>10</sub> values for injury 14 days
after the V2 and R1 exposure timings were 0.03 and 0.18 g ae ha<sup>-1</sup>,
respectively, for dicamba and 35 and 31 g ae ha<sup>-1</sup>, respectively for
2,4-D. For soybean grain yield, ED<sub>10</sub> values for dicamba were 4.61
and 1.66 g ha<sup>-1</sup> at the V2 and R1 timings, respectively, and 34 g ha<sup>-1</sup>
for 2,4-D, combined across exposure timings. Additionally, dicamba/glyphosate-resistant
soybean yield response to 2,4-D (ED<sub>10</sub> = 34 g ha<sup>-1</sup>) was
similar to glyphosate-resistant soybean (ED<sub>10</sub> = 34 g ha<sup>-1</sup>)
and the addition of a full rate of dicamba to 2,4-D tank-contamination did not
increase soybean yield response to 2,4-D (ED<sub>10</sub> = 59 g ha<sup>-1</sup>).
Thus, no interaction of 2,4-D plus dicamba was apparent on the
dicamba/glyphosate-resistant soybean and practices to mitigate exposure to
2,4-D on these soybeans would be no different than other sensitive varieties.</p>
<p> An
experiment was conducted to evaluate soybean response to dicamba in conjunction
with other labeled postemergence herbicides that are known to cause soybean injury,
such as lactofen, acetochlor, and 2,4-DB. Soybean injury at 28 days after the
R1 application was influenced primarily by the timing of dicamba exposure
rather than the labeled POST herbicide, with up to 14% injury from POST
herbicides alone and up to 37% injury from dicamba exposure at a dose of 5.6 g
ha<sup>-1</sup> alone at R1. Soybean yield reduction in response to dicamba
alone was greater during the 2017 growing season with a 37% reduction in yield
from dicamba exposure at R1 in 2017 compared with a 17% reduction in 2018.
Regardless of the difference in yield response between years, the primary
factor that influenced yield was the timing of dicamba exposure. In general,
glyphosate-resistant soybean response to a reduced rate of dicamba was not
influenced by additional postemergence herbicides applied at either the V3 or
R1 growth stage.</p>
<p> Controlled
environment experiments were conducted to evaluate the relative volatilization
of dicamba formulations applied with drift reduction agents, turbid water
carrier, ions in spray solution, and a spray solution pH range. Drift reduction
agents and turbid water carrier did not affect dicamba volatilization. Spray pH
levels of 4 and above did not result in increased levels of volatilization,
while a spray pH of 3 increased volatilization by 2.8X and 3.9X for the DGA +
VG and BAPMA formulations, respectively, compared with each respective dicamba
formulation applied alone at a native pH of 5.4 and 6.4, respectively. Of the
ions tested, diammonium and ferrous sulfate increased dicamba volatilization by
5X and 9X for the DGA + VG formulation, respectively, and 11X for the BAPMA
formulation compared with dicamba alone. Additionally, the sulfate and chloride
anions present in other ions tested did not cause an increase in
volatilization. These results indicate the importance of spray application
parameters and the continual attention to details such as tank-mix pH and
carrier water ion content that must be practiced prior to an application of a
synthetic auxin herbicide to avoid off-target movement. </p>