Herbicide Safeners Increase Creeping Bentgrass (Agrostis stolonifera) Tolerance to Pinoxaden and Affect Weed Control

The herbicide pinoxaden is a phenylpyrazoline inhibitor of acetyl coenzyme A carboxylase. Research was conducted to determine the effects of pinoxaden (90 g ai ha⁻¹) alone and in combination with herbicide safeners on creeping bentgrass injury as well as perennial ryegrass and roughstalk bluegrass control. Greenhouse experiments determined that herbicide safeners cloquintocet-mexyl, fenchlorazole-ethyl, and mefenpyr-diethyl were more effective in reducing creeping bentgrass injury from pinoxaden than benoxacor, isoxadifen-ethyl, and naphthalic-anhydride. Other experiments determined that creeping bentgrass injury from pinoxaden decreased as rates (0, 23, 45, 68, 90, 225, or 450 g ha⁻¹) of cloquintocet-mexyl, fenchlorazole-ethyl, and mefenpyr-diethyl increased. On the basis of creeping bentgrass responses to various safener rates, safeners were applied at 68 and 450 g ha⁻¹ in additional experiments to evaluate their effects on pinoxaden (90 g ha⁻¹) injury to creeping bentgrass and efficacy against perennial ryegrass and roughstalk bluegrass. In these experiments, safeners mefenpyr-diethyl and cloquintocet-mexyl reduced pinoxaden-induced creeping bentgrass injury (from 25 to ≤ 5%) more than fenchlorazole-ethyl at 2 wk after treatment. Safeners reduced pinoxaden efficacy against roughstalk bluegrass. Perennial ryegrass was controlled > 80% by pinoxaden and herbicide safeners did not reduce control. Field experiments should evaluate pinoxaden in combination with cloquintocet-mexyl and mefenpyr-diethyl to optimize safener : herbicide ratios and rates for creeping bentgrass safety as well as perennial ryegrass and roughtstalk bluegrass control in different climates and seasons. Nomenclature: Cloquintocet-mexyl; fenchlorazole-ethyl; mefenpyr-diethyl; pinoxaden; creeping bentgrass, Agrostis stolonifera L. AGSST; perennial ryegrass, Lolium perenne L. LOLPE; roughstalk bluegrass, Poa trivialis L. POATR