Date of Graduation

12-2021

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Jason Norsworthy

Committee Member

Trent Roberts

Second Committee Member

Tom Barber

Third Committee Member

Jeremy Ross

Fourth Committee Member

Ed Gbur

Keywords

Fertilization, Herbicide, Herbicide injury, Herbicide sensitivity, Irrigation, Off-target movement, Planting date, Rate, Relative yield, Synthetic Auxin

Abstract

Although the integration of dicamba as a postemergence (POST) herbicide has proven useful in controlling many herbicide-resistant weeds, its damage to soybean at low rates, such as supplied by drift and volatility, has been well-documented. Injury to other crops, such as rice, from off-target movement of dicamba and other commonly used herbicides, such as glyphosate, may also occur. Practical options for mitigating injury and yield loss to soybean and other crops from dicamba off-target movement could prove beneficial if dicamba continues to be used during summer months. Experiments were conducted to determine the effects of multiple agricultural practices, including cultivar selection, planting date, irrigation, and fertilization, to soybean injured by a low dose of dicamba, and possible rice injury from dicamba and glyphosate. In an experiment evaluating sensitivity of soybean cultivars to a low dose of dicamba, only ‘Eagle DrewSoy’ maintained high relative yield and low visible injury, and was, therefore, considered as a likely candidate for enhanced tolerance to dicamba. Soybean exposed to a low dose of dicamba at the V3, R1, or sequentially at V3 followed by R1 growth stages that was planted after mid-June had significant yield loss compared to the nontreated that was planted at the same date. Above-average rainfall in the irrigation experiment may have negated the likelihood of finding differences in yield and injury between regimes. In the fertilization experiment, there was a negative effect of dicamba treatments applied at reproductive growth stages on soybean injury, but not relative yield. Fertilizer applications made shortly after the occurrence of injury did not aid in the recovery of soybean yield. Application timings before reproductive stages were reached could have provided different results by allowing fertilizers more time to aid soybean recovery from dicamba injury. For experiments evaluating the effect of low rates of glyphosate and dicamba on rice, greater crop injury and yield loss occurred when glyphosate and dicamba were mixed than when glyphosate was applied alone. This research shows that soybean injury and yield loss differ among soybean cultivars and planting dates, but not irrigation regimes in a wet year or fertilizer additions at the timings and rates used in this experiment. Rice injury and yield loss from glyphosate off-target movement may be exacerbated by the presence of dicamba in addition to glyphosate.

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