Degree

Doctor of Philosophy (PhD)

Department

SPESS

Document Type

Dissertation

Abstract

Two separate field studies were conducted in 2024 and 2025 at the LSU Agricultural Center Dean Lee Research and Extension Center near Alexandria, LA to evaluate the critical period of weed control (CPWC) and the effect of preemergence residual herbicides (PRE) on the critical time of weed removal (CTWR) in Louisiana soybean. In 2024 there was no clear depiction of the CPWC with overlapping intervals at the six-week emergence and removal interval. However, in 2025 the CPWC was observed within 2.8 to 10.23 wks following soybean emergence these results suggest the CPWC can shift across years from influential factors such as varying weed density. In 2024, the critical time of weed removal was observed at 5.43 weeks, 5.85 weeks, and 5.94 weeks for the nontreated comparison, flumioxazin treatments, and the flumioxazin:pyroxasulfone:metribuzin treatment, respectively. In 2025, differences were observed among the no PRE or nontreated observations suggesting the CTWR was at 6.04 weeks when a residual herbicide was not applied. Field studies were conducted in 2024 and 2025 at the H. Rouse Caffey Rice Research Station near Crowley, Louisiana to evaluate the varietal response of non-Clearfield® medium and long grain rice varieties to simulated imazethapyr carryover. Rice injury was observed at 14 and 21 days after emergence (DAE) when imazethapyr was applied at 5 to 35 g ha-1 among PVL03, Jupiter, and Avant compared to the nontreated. However, early season crop injury observed only correlated to rice yield loss to PVL03 when imazethapyr was applied at 35 g ha-1. Two separate field studies were conducted in 2024 and 2025 at the H. Rouse Caffery Rice Research Station near Crowley, Louisiana to evaluate the efficacy of iptriazopyrid for grass, broadleaf, and sedge control. Greater weed control was observed for all treatments across all grass, broadleaf, and sedge species when iptriazopyrid was applied in close conjunction with permanent flood establishment. However, in some instances inconsistent control was observed when iptriazopyrid was applied at rates < 100 g ai ha-1 suggesting that 100 g ha-1 should be the minimum recommendation. Additional research suggests sequential applications should be considered for broader spectrum weed control.

Date

3-26-2026

Committee Chair

Dr. Connor Webster

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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Available for download on Thursday, March 24, 2033

Included in

Weed Science Commons

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