Date of Graduation

12-2023

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Norsworthy, Jason K.

Committee Member

Butts, Thomas R.

Second Committee Member

Mauromoustakos, Andronikos T.

Third Committee Member

Roberts, Trenton L.

Keywords

Florpyrauxifen-benzyl; Herbicide; Rice; Soybean

Abstract

Frequent off-target movement occurrences to soybean [Glycine max (L.) Merr.], rice (Oryza sativa L.) injury, and a lack of barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] control followed the commercial launch of florpyrauxifen-benzyl in 2018. Florpyrauxifen-benzyl is a synthetic auxin, Herbicide Resistance Action Committee (HRAC)/Weed Science Society of America (WSSA) Group 4 herbicide used for postemergence weed control in rice and labeled for application at 30 g ae ha-1. Previous research documented that soybean was susceptible to injury following spray applications of florpyrauxifen-benzyl at less-than-labeled rates, and certain varieties of rice are less tolerant to spray-applied florpyrauxifen-benzyl at 30 g ae ha-1. An alternative application method to safely apply florpyrauxifen-benzyl and reduce off-target movement was needed. As a result, experiments were conducted to 1) evaluate rice varietal tolerances to applications of florpyrauxifen-benzyl coated on urea at 30 and 60 g ae ha-1, 2) investigate the weed control spectrum and size influence on rice weed control provided by florpyrauxifen-benzyl coated on urea, 3) determine the impact of flood timing and flood loss on rice weed control following an application of florpyrauxifen-benzyl coated on urea, and 4) determine if coating florpyrauxifen-benzyl on urea minimizes the risk of injury to soybean compared to spray-applied. Generally, florpyrauxifen-benzyl caused variable levels of rice injury based on specific cultivars tested. Coating florpyrauxifen-benzyl on urea did not completely safen rice to the herbicide when applied at a commercially labeled rate (30 g ae ha-1). Florpyrauxifen-benzyl coated on urea was less effective at controlling hemp sesbania and barnyardgrass when rice flood establishment was delayed due to larger weed sizes compared to earlier application timings. Flood loss timings had little impact on hemp sesbania, yellow nutsedge, and barnyardgrass control following an application of florpyrauxifen-benzyl coated on urea. Coating urea with florpyrauxifen-benzyl alone provided comparable levels of yellow nutsedge and hemp sesbania control compared to the herbicide when spray-applied, but barnyardgrass was not effectively controlled. The addition of penoxsulam to florpyrauxifen-benzyl on urea did provide effective barnyardgrass control. Rice flatsedge at approximately 10- and 25-cm was effectively controlled by florpyrauxifen-benzyl, regardless of whether it was spray-applied or coated to urea. Coating florpyrauxifen-benzyl on urea significantly reduced soybean injury in narrow- and wide-row systems compared to spraying the herbicide. Soybean yield and yield components were generally not impacted by low rates of florpyrauxifen-benzyl coated on urea whereas low rates from the spray application greatly reduced yield. Utilizing urea to deliver florpyrauxifen-benzyl did not increase the likelihood of volatilization of the herbicide under any soil moisture condition. Findings from this research will better enable farmers and crop consultants to make informed management decisions with herbicide recommendations with the opportunity to apply florpyrauxifen-benzyl using an alternative application method more safely.

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