Velvet and Creeping Bentgrass Tolerance to Fenoxaprop

Abstract

The tolerance of velvet bentgrass (Agrostis canina L.) to the herbicide fenoxaprop is not known. In greenhouse experiments velvet bentgrass cultivars SR7200 and Vesper had a much greater degree of tolerance to fenoxaprop at rates ranging from 0.01 to 0.30 kg·ha-1 relative to L-93 creeping bentgrass (Agrostis stolonifera L.). SR7200 and Vesper were tolerant to fenoxaprop at 0.15 kg·ha-1 or lower and growth reductions did not exceed 10% at the highest fenoxaprop rate of 0.30 kg·ha-1. In contrast, growth reduction of L-93 creeping bentgrass was evident at the lowest application of fenoxaprop at 0.01 kg·ha-1 and increased as fenoxaprop rates increased, reaching as high 58% at 0.30 kg·ha-1. Field experiments were conducted in 2002 and 2003 to compare the tolerance of established SR7200 velvet bentgrass and Penn A-4 creeping bentgrass maintained at 3.2 mm to three sequential applications at 21 day intervals of fenoxaprop at 0.02, 0.04, and 0.07 kg·ha-1. Turf quality of SR7200 was equal to the untreated following all fenoxaprop applications except the third sequential application at 0.07 kg·ha-1. Penn A-4 turf quality was consistently reduced compared to the untreated following fenoxaprop applications of 0.04 and 0.07 kg·ha-1. Turf density of SR7200 was not affected by three sequential applications of fenoxaprop at 0.02 and 0.04 kg·ha-1 but was reduced by 8% at 0.07 kg·ha-1. Penn A-4 turf density was reduced by 10 and 33% following three sequential applications of fenoxaprop at 0.04 and 0.07 kg·ha-1, respectively. Results from these studies showed that the velvet bentgrass cultivars were more tolerant to fenoxaprop, compared to the creeping bentgrass cultivars evaluated. Chemical names used: (+)-ethyl2-[4-[(6-chloro-2-benzoxazolyl)oxy]p henoxy] propanoate (fenoxaprop). 3,5-pyridinedicarbothioic acid, 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-S,S-dimethylester (dithiopyr).