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20 February 2024 Influence of fluazifop timing and rate on johnsongrass (Sorghum halepense) control in ACCase-resistant grain sorghum (Sorghum bicolor)
Jacob Fleming, Jason K. Norsworthy, Muthukumar Bagavathiannan, Tom Barber
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Abstract

Genetic similarities between johnsongrass and grain sorghum leave producers with limited herbicide options for postemergence johnsongrass control. TamArkTM grain sorghum with resistance to acetyl-CoA carboxylase-inhibiting herbicides was developed through a collaboration between the University of Arkansas System Division of Agriculture and Texas A&M AgriLife Research. Two field experiments were conducted in 2021 in two locations each: Keiser and Marianna, AR, or Fayetteville and Marianna, AR. The objective of the first was to determine the optimal rate and application timing of fluazifop-butyl for control of natural johnsongrass populations in a noncrop setting, and the objective of the second was to evaluate johnsongrass control and TamArkTM grain sorghum tolerance in response to fluazifop-butyl applied at different timings and rates based on crop growth stage. The highest levels of johnsongrass control occurred when sequential applications of fluazifop-butyl were utilized. All sequential treatments provided at least 80% johnsongrass control at any rate or application timing tested. A single application of fluazifop-butyl provided greater than 90% johnsongrass control when applied at 210 g ai ha–1 to johnsongrass with fewer than 6 leaves. Weed size played a role in achieving high levels of johnsongrass control. Greater than 90% control was achieved when johnsongrass had 6 leaves or fewer at the initial application for the sequential application treatments. A single application of fluazifop-butyl at 105 g ai ha–1 resulted in no more than 82% johnsongrass mortality at any application timing. TamArk™ grain sorghum injury did not exceed 6% at any application timing or rate. It was therefore considered to be safe even if the initial application was made before the 6-leaf crop stage. Because no unacceptable levels of injury were observed with TamArk™ grain sorghum for fluazifop-butyl, johnsongrass size at the time of application should be the most critical aspect for control with this herbicide.

Nomenclature: fluazifop-butyl; johnsongrass, Sorghum halepense (L.) Pers.; grain sorghum, Sorghum bicolor (L.) Moench

Jacob Fleming, Jason K. Norsworthy, Muthukumar Bagavathiannan, and Tom Barber "Influence of fluazifop timing and rate on johnsongrass (Sorghum halepense) control in ACCase-resistant grain sorghum (Sorghum bicolor)," Weed Technology 38(1), 1-7, (20 February 2024). https://doi.org/10.1017/wet.2023.47
Received: 8 February 2024; Accepted: 12 July 2024; Published: 20 February 2024
KEYWORDS
TamArk™
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