Doctoral Dissertations

Orcid ID

https://orcid.org/0000-0001-8592-0727

Date of Award

5-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

James T. Brosnan

Committee Members

David M. Butler, Travis W. Gannon, Rebecca G. Bowling

Abstract

Tetflupyrolimet, a new herbicide developed by FMC Corporation, targets dihydroorotate dehydrogenase (DHODH), effectively inhibiting de novo pyrimidine biosynthesis in various grass species. This dissertation synthesizes findings from field, greenhouse, and laboratory trials conducted between 2021 and 2024, aimed at better understanding the applications of tetflupyrolimet in turfgrass systems. First, this included assessing turfgrass tolerance to tetflupyrolimet in controlling problematic species such as Poa annua and smooth crabgrass (Digitaria ischaemum). Five turfgrass species relevant to Tennessee were assessed at cutting heights ranging from 3.8 to 12.5 mm across different seasons, revealing that warm-season turfgrasses exhibited no adverse effects to as high as 3200 g ha-1. Response of cool-season grasses varied with an overall trend for cool-season species to be more tolerant to applications made in spring than fall. Efficacy for preemergence (PRE) control of smooth crabgrass fluctuated yearly, but tetflupyrolimet (400 g ha-1) in mixture with pyroxasulfone (128 g ha-1) and rimsulfuron (35 g ha-1) proved effective in controlling herbicide-resistant Poa annua. Additionally, research was conducted to understand the influence of soil texture on tetflupyrolimet activity, revealing significant variations in efficacy between sandy versus clay loam soils, with higher effectiveness with applications made to the coarser textured medium. Data collected suggest that matric potential differences amongst soil-types may explain this response with water being more accessible to seedling weeds in coarser textured mediums with overall moisture content is fixed across soil types. Offering tetflupyrolimet application rates based on soil texture may enhance herbicide performance under various soil-moisture conditions. Furthermore, the lateral movement of tetflupyrolimet was investigated under field capacity and saturated soil-conditions. Regardless of soil moisture content, tetflupyrolimet maximum lateral movement was limited to 1.1 meters, significantly less than pronamide exhibited greater mobility. This experiment indicated that maintaining a buffer of at least 1.1 meters from sensitive grass species could minimize the risk of non-target effects of tetflupyrolimet applications in turfgrass. Overall, the studies support tetflupyrolimet use in turfgrass management, giving managers a novel tool in mitigating herbicide resistance within the troublesome grassy weed, Poa annua.

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