Date of Graduation

12-2015

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Jason K. Norsworthy

Committee Member

Tom Barber

Second Committee Member

Edward Gbur

Third Committee Member

Kris Brye

Keywords

Biological sciences; Agronomy; Weed control; Weed science

Abstract

New herbicide-resistant soybean traits will increase the number of herbicides that can be applied in soybean and change the technology currently used to make herbicide applications in soybean. Palmer amaranth (Amaranthus palmeri) remains one of the most difficult weeds to manage in soybean and thus is the primary focus of this research. Therefore, experiments were conducted to investigate Palmer amaranth temporal emergence, control of common Arkansas weeds with new soybean herbicide programs, and the effect of application technology on dicamba-containing tank mixtures. Palmer amaranth emergence exceeded 400 plants m-2 for tillage treatments in 2013 and 2014, and tillage events typically increased emergence compared to no-tillage. The addition of isoxaflutole and mesotrione (HPPD-inhibitors) to soybean herbicide programs PRE improved control more than dicamba or 2,4-D (synthetic auxins) PRE. Herbicide programs that included HPPD-inhibitors EPOST improved control of Palmer amaranth more than programs with synthetic auxins. However, synthetic auxins applied LPOST controlled Palmer amaranth better than HPPD-inhibitors LPOST. Herbicide programs that included synthetic auxins or HPPD-inhibitors improved control of pitted morningglory but did not improve control of prickly sida and barnyardgrass compared to current standard herbicide programs. Applicator-controlled variables such as nozzle selection, spray volume, and groundspeed did not affect the efficacy of many dicamba-containing tank mixtures investigated. However, a tank mixture of the products Roundup PowerMax + Engenia produced an antagonistic effect on large barnyardgrass. Additionally, Palmer amaranth and barnyardgrass control was higher at 187 L ha-1 for Engenia + Roundup for the TTI nozzle than at 94 L ha-1. These results show that new technologies will improve control of some weeds in soybean, but the new technologies need to be applied using effective spray nozzles and spray volumes.

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