Alternative Strategies for Weed Control in Creeping Bentgrass

Creeping bentgrass (CBG) (Agrostis stolonifera L.) is the most widely used cool-season turfgrass species on golf course fairways and tees in the United States, but it is tolerant of few post-emergence herbicides. Commercial herbicide development is currently focused on providing superintendents with herbicides that pose minimal environmental impact and can be used effectively at lower application rates than older alternatives. However, few of these products are safe for use on CBG. Several projects were conducted to evaluate alternative strategies to increase CBG herbicide tolerance.

Plants naturally contain enzymatic systems that metabolize xenobiotics. The interspecies variability in these enzymes is exploited by selective herbicides that are rapidly metabolized by desirable plants but not target weeds. Herbicide safeners can further exploit these differences and increase herbicidal selectivity in corn and wheat, but they have not been investigated in turfgrass.

In one project, glasshouse research investigated the efficacy of herbicide safeners for improving CBG tolerance to amicarbazone, bispyribac-sodium, fenoxaprop-p-ethyl, imazapic, quinclorac or topramezone. The herbicide safener cloquintocet-mexyl reduced CBG injury from topramezone and did not affect topramezone efficacy against large crabgrass or goosegrass.

Cytochrome P450 monooxygenases (P450’s) are an enzyme superfamily often responsible for metabolizing xenobiotics. An experiment evaluated CBG in hydroponic culture to determine if P450’s influence CBG tolerance to topramezone. Known P450 inhibitors increased CBG injury caused by topramezone, suggesting creeping bentgrass tolerance to topramezone is influenced by cytochrome P450-catalyzed metabolism.

Another project investigated safeners in combination with the herbicide pinoxaden. Glasshouse experiments determined that the safeners cloquintocet-mexyl, fenchlorazole-ethyl, and mefenpyr-diethyl reduced CBG injury in a rate-dependent manner. The safeners did not affect perennial ryegrass control, but reduced roughstalk bluegrass control. However, these reductions were offset by CBG injury reductions.

Another project investigated novel triketone p-HPPD inhibitors for their safety to CBG and herbicidal efficacy against goosegrass and crabgrass. Previous research suggests that 2-benzoyl-1,3-cyclohexanedione compounds with alkyl substitutions on the cyclohexane moiety have more efficacy against grassy weeds. We synthesized 2-(2,4-dichlorobenzoyl)cyclohexane-1,3-dione compounds with various alkyl substituents on the cyclohexanedione moiety and evaluated their efficacy against turfgrass weeds. The 5,5-dimethyl-substituted compound had efficacy against goosegrass and did not cause injury to CBG.