Date of Graduation

8-2024

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

Barber, Lon T.

Second Committee Member

Roberts, Trenton L.

Third Committee Member

Thrash, Benajmin C.

Fourth Committee Member

Mills, Anthony

Keywords

Herbicide; Weed science

Abstract

Palmer amaranth [Amaranthus palmeri (S.) Wats.] and waterhemp [Amaranthus tuberculatus (Moq.) Sauer] ranks among the most troublesome weeds of soybean [Glycine max (L.) Merr.], having evolved resistance to multiple herbicide sites of action. Bayer CropScience has announced its intentions to launch Convintro™ brand herbicides, one being a three-way premixture for use preplant until 3 d after planting in soybean. The premixture will include diflufenican (WSSA Group 12), metribuzin (WSSA Group 5), and flufenacet (WSSA Group 15) (DFF-containing premixture), adding a new site of action for use in soybean throughout the United States. In 2022 and 2023, field trials were conducted at four locations in Arkansas and two in Michigan. Field experiments evaluated the sensitivity of several crops to simulated diflufenican carryover or sprayer contamination with the DFF-containing premixture. At 14 d after emergence (DAE), injury was <10% for all crops evaluated, with no injury detected by 28 DAE for simulated carryover experiments. Injury was <15% for cotton (Gossypium hirsutum L.), soybean, and rice (Oryza sativa L.), with no crop response occurring for corn (Zea mays L.) or grain sorghum (Sorghum bicolor L.) at the final evaluation for sprayer contamination experiments. The risk for injury appears low from diflufenican carryover or sprayer contamination with the DFF-containing premixture. Additionally, application timings of the DFF-containing premixture were evaluated for soybean tolerance and weed control and the tolerance of multiple soybean cultivars to diflufenican or the DFF-containing premixture. Up to 60% injury to soybean occurred at a 2X rate of the DFF-containing premixture at 14 d after planting (DAP), increasing the closer the application occurred to crop emergence. By 42 DAP, soybean injury was <15% for the 1X rate of the DFF-containing premixture regardless of site year. Control of five weeds, including broadleaves and grasses, from a 1X rate of the DFF-containing premixture ranged from 81% to 98%, regardless of application timing 28 DAP. By 42 DAP, the 14-d preplant application timing was typically the least effective in weed control compared to the additional application timings. In the soybean cultivar study, metribuzin sensitivity rating did not impact injury to the crop, even on a high pH soil. Injury from a 1X and 2X rate of diflufenican or the DFF-containing premixture never exceeded 20% in the metribuzin cultivar study. With the DFF-containing premixture as an effective option, the herbicide was evaluated against commonly used PRE herbicides in soybean for residual control of Amaranthus species. At 28 DAT, the DFF-containing premixture was more effective in reducing Amaranthus species than acetochlor. By 56 DAT, the DFF-containing premixture was comparable to or more effective than all herbicides evaluated. Finally, the DFF-containing premixture was evaluated as part of a season-long herbicide program. At 28 DAP, the DFF-containing premixture was most effective in controlling Palmer amaranth and prickly sida (Sida spinosa L.) (>90%). By 70 DAP, all weeds were controlled >93%; however, plots that received two sequential applications postemergence had superior weed control. Overall, the DFF-containing premixture appears to be an additional tool producers can utilize to control Amaranthus species.

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