Semester of Graduation

Fall 2025

Degree

Master of Science (MS)

Department

Plant, Environmental, and Soil Sciences

Document Type

Thesis

Abstract

A field study was initiated in the fall of 2023 and repeated in 2024 at the LSU AgCenter Northeast Research Station near St. Joeseph, LA, to determine the impact of fall-applied soil residual herbicide at different growth stages (spike and one-leaf stage) on grass cover crop species, cereal rye and black oats. In most instances, clomazone (631 g ai ha-1) and treatments containing the higher rates of metribuzin (263 g ai ha-1)resulted in the greatest amount of cover crop injury both years, with biomass impacted by clomazone both years and in one of two years with the treatments containing the higher rate of metribuzin. A more pronounced cover crop visual injury was observed with S-metolachlor (1,421 g ai ha-1), metribuzin (146 g ai ha-1) containing treatments, and pyroxasulfone plus fluthiacet-methyl (141 g ai ha-1) in 2024 vs. 2023. This was attributed to 2.7-times increased rainfall received within 14 DAT of fall-applied residual herbicides in 2024 resulting in waterlogged soil and potentially reducing plants’ ability to metabolize those herbicides. Injury was more pronounced at the spike stage application timing, but the difference was not evident in cover crop biomass reduction. In 2024, cover crop biomass was only negatively impacted with clomazone applied to black oats while in 2025 biomass was reduced following the application of clomazone and treatments containing the higher rate of metribuzin, regardless of the cover crop species. Also, in 2025, cereal rye was more sensitive to fall-applied herbicides at the spike stage while black oats were more sensitive at the later timing.

A separate field study was initiated in the fall of 2023 and repeated in 2024 at the LSU AgCenter Northeast Research Station near St. Joeseph, LA to determine the impact of fall-applied herbicide of S-metolachlor at 1421 g ai ha-1 or no fall-applied herbicide, cover crop of cereal rye or no cereal rye, and termination timing on Italian ryegrass control with glufosinate or paraquat applied 4 or 2 weeks before planting or at planting. Italian ryegrass control was maximized with the combination of cereal rye cover crop and S-metolachlor applied at the spike stage of the cover crop in the fall. Cereal rye alone controlled Italian ryegrass 70 to 73% 8 to 12 WAP while S-metolachlor alone resulted in 76 to 84% control. The combination resulted in 97 to 99% 8 to 12 WAP. In addition, Italian ryegrass tiller count, reproductive tillers, and biomass reduction were greatest with the cereal rye and S-metolachlor combination in 2024. In 2025, only the addition of cereal rye cover crop to S-metolachlor had a positive impact on those parameters.

Date

11-3-2025

Committee Chair

Miller, Donnie; Jha, Prashant; Webster, Lucas; Foster, Matthew

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