Date of Graduation

5-2018

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Jason Norsworthy

Committee Member

Tom Barber

Second Committee Member

Bob Scott

Third Committee Member

Edward Gbur

Fourth Committee Member

Larry Purcell

Fifth Committee Member

Trent Roberts

Keywords

Dicamba, Drift, Soybean, Volatility

Abstract

Commercial launch of cotton with resistance to dicamba, glyphosate, and glufosinate occurred in 2015 and launch of soybean with resistance to dicamba and glyphosate occurred in early 2016. It is likely that non-dicamba-resistant soybean will be planted in close proximity to dicamba-resistant soybean and cotton. Therefore, experiments were conducted to examine the distance dicamba moves during an application using commercial application equipment, as well as the effect the drift events have upon soybean offspring. Additional experiments were designed to investigate the effect glyphosate addition to dicamba has upon soybean growth and yield as well as possible effects on offspring. Lastly, an experiment was designed to determine the extent of secondary (volatile) drift of two formulations of dicamba under mid-summer conditions. Drift of dicamba exceeded 150 m in some drift trials (5% soybean injury). Drift trials established at early reproductive stages were more damaging to parent soybean; however, applications to late reproductive soybean were more detrimental to the soybean offspring. Percent of parent pods malformed resulting from dicamba drift events at the R5 growth stage displayed the highest correlation coefficients with offspring emergence (r = -0.37, p = 0.0082), vigor (r = -0.57, p = < 0.0001), injury (r = 0.93, p = < 0.0001), and amount of plants injured (r = 0.92, p = < 0.0001). When low rates of glyphosate were added to low rates of dicamba and applied to soybean at R1 growth stage, leaf malformation at 28 days after application (DAA) was increased over low rates of dicamba alone. Dicamba also caused damaging effects to soybean offspring; however, the addition of glyphosate did not increase further impact on soybean offspring. Diglycolamine (DGA) and N,N-Bis-(aminopropyl) methylamine (BAPMA) forms of dicamba are suspected to be similar in terms of primary drift; however, injury caused by secondary drift from BAPMA dicamba was less than DGA dicamba at 21 days after application (DAA). These results document that caution should be used to minimize the risk for damage to neighboring non-dicamba-resistant soybean fields.

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