Clethodim suppresses hair fescue in lowbush blueberry

Hair fescue (Festuca filiformis Pourr.) is a tuft-forming perennial grass of concern in lowbush blueberry (Vaccinium angustifolium Ait.) as tufts form dense sods that reduce lowbush blueberry yield and inhibit harvest. Although generally tolerant to ACCase-inhibiting herbicides, injury to some Festuca spp. following clethodim applications has been reported. ACCase-inhibiting herbicides are important for non-bearing and bearing year perennial grass management in lowbush blueberry but have not been extensively evaluated for hair fescue management. The objectives of this research were to (1) determine the relative efficacy of foramsulfuron, fluazifop-P-butyl, sethoxydim, and clethodim on hair fescue, and (2) determine if foramsulfuron tank mixtures with fluazifop-P-butyl, sethoxydim, and clethodim improve hair fescue suppression. None of the herbicides evaluated caused unacceptable injury to lowbush blueberry. Foramsulfuron (35 g a.i. ha−1) reduced hair fescue total tuft density, flowering tuft density, and flowering tuft inflorescence number. Fluazifop-P-butyl (250 g a.i. ha−1) and sethoxydim (495 g a.i. ha−1) caused variable levels of visual injury to hair fescue and did not reduce total tuft density, flowering tuft density, or flowering tuft inflorescence number. Clethodim (91 g a.i. ha−1), however, caused >50% visual injury to hair fescue and reduced hair fescue total tuft density, flowering tuft density, and flowering tuft inflorescence number. Fluazifop-P-butyl and sethoxydim tank mixtures with foramsulfuron did not increase hair fescue suppression relative to foramsulfuron alone. A foramsulfuron + clethodim tank mixture provided equivalent hair fescue suppression as either herbicide applied alone. Foramsulfuron and clethodim should therefore be used in rotation rather than tank mixture to manage hair fescue in lowbush blueberry.