Date of Award

12-2011

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant Sciences

Major Professor

James T. Brosnan

Committee Members

Brandon J. Horvath, Dean A. Kopsell, Thomas C. Mueller

Abstract

Herbicidal inhibitors of 4-hydroxyphenylpyruvate dioxygenase (HPPD) such as mesotrione, topramezone and tembotrione were evaluated in greenhouse experiments for activity against bermudagrass. While topramezone and tembotrione exhibited greater activity than mesotrione, none of these herbicides provided acceptable bermudagrass control. These herbicides reduced leaf tissue chlorophyll and carotenoid pigment concentrations in bermudagrass. Changes in turfgrass pigmentation were quantified using HPLC analogy as well as evaluations of visual bleaching and measurements of chlorophyll fluorescence yield (Fv/Fm). Results indicated that these more expeditious methods of evaluating HPPD-inhibiting herbicide activity (visual evaluations and Fv/Fm) cannot be used to successfully predict turfgrass pigmentation following applications.

Mesotrione and topramezone are efficacious against small (< 2-tiller) smooth crabgrass plants. Field studies were conducted in 2010 and 2011 to evaluate efficacy of mesotrione and topramezone on 3- to 5-tiller smooth crabgrass in combination with different rates of nitrogen fertilizer. Greenhouse experiments were conducted to evaluate the dose-response of smooth crabgrass to mesotrione and topramezone with nitrogen fertilizer. Increased mesotrione and topramezone efficacy was observed with added nitrogen fertilizer in all experiments. Greenhouse experiments indicate that nitrogen fertilizer reduces the amount of mesotrione and topramezone required to control smooth crabgrass. Further research indicated that this enhancement was due to increased activity in the shoot meristem which could be caused by increased translocation of the herbicide.

Dallisgrass (Paspalum dilatatum), bermudagrass (Cynodon spp.) and smooth crabgrass (Digitaria ischaemum) are problematic weeds in turfgrass throughout the southeastern United States. Infestations negatively affect the aesthetic and functional quality of desirable turfgrass stands. Additionally, these species compete with turfgrasses for light, water, and nutrients. Therefore, selective control of these species is warranted.

The herbicide fluazifop-p-butyl is commonly applied to control dallisgrass in tall fescue (Festuca arundinacea); however, control is often short-lived. A two-year field study was conducted to evaluate the efficacy of several herbicide combinations with fluazifop-p-butyl for dallisgrass control when applied at different growing degree-day- (GDD) based application timings. Results of this research indicate that application timing significantly impacts long-term dallisgrass control with fluazifop-p-butyl.

Results of experiments presented here indicate simple strategies can be used to influence the efficacy of herbicides against problematic turfgrass weeds.

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