Date of Graduation

5-2020

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Tom Barber

Committee Member

Jason Norsworthy

Second Committee Member

Edward Gbur

Third Committee Member

Jason Kelley

Fourth Committee Member

Trent Roberts

Keywords

Resistance, herbicides, grain sorghum, Inzen, nicosulfuron

Abstract

Grain sorghum is typically grown as a rotational crop in Arkansas because of its many benefits, one being the effective control of Palmer amaranth through the use of atrazine. However, limited options exist for postemergence (POST) control of weedy grasses within the crop. Inzen™ grain sorghum is the result of a nicosulfuron resistant weedy sorghum biotype cross-bred with a commercial line of grain sorghum. Inzen™ allows for safe use of over-the-top applications of nicosulfuron within the crop. Nicosulfuron is an acetolactate synthase (ALS)-inhibiting herbicide, which has historically been used in corn for control of weedy grasses. Experiments were conducted in 2016 and 2017 to (1) evaluate the tolerance of Inzen™ grain sorghum to various herbicides in Weed Science Society of America Group 2 ALS-inhibiting herbicides, (2) evaluate weed control programs utilizing nicosulfuron, and (3) determine the sensitivity of conventional grain sorghum to low rates of nicosulfuron and glufosinate. Results indicate Inzen™ grain sorghum was tolerant to ALS-inhibiting herbicides evaluated when applied directly to the soil prior to crop emergence (PRE). When ALS-inhibiting herbicides were applied to Inzen™ grain sorghum at the V4 growth stage, a high level of resistance was observed to all herbicides, with the exception of bispyribac-Na, which resulted in 20% visible injury and a 35% yield reduction. Additionally, weed control programs utilizing S-metolachlor preemergence and nicosulfuron + atrazine applied POST resulted in a yield increase along with acceptable control of both Palmer amaranth and johnsongrass. Finally, conventional grain sorghum appeared to be most sensitive to low rates of nicosulfuron and glufosinate at V8, flagleaf, or heading growth stages. Yield reductions of up to 96% were observed from rates of nicosulfuron equivalent to 1/10X of a labeled use rate.

Nomenclature: Inzen; atrazine; byspyribac; glufosinate; nicosulfuron; S-metolachlor; johnsongrass, Sorghum halepense L. Pers.; Palmer amaranth, Amaranthus palmeri S. Wats.; corn, Zea mays L.; grain sorghum, Sorghum bicolor L. Moench ssp. bicolor

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