Tolerance of Four Festuca Species to Ethofumesate and Prodiamine

Abstract

Festuca species are being seeded into golf course roughs and natural or out-of-bound areas as alternative turfgrasses to replace perennial ryegrass (Lolium perenne L.) in the mid-Atlantic region. The tolerance of fine-leaf fescues to herbicides targeted for annual bluegrass (Poa annua L.) control, such as ethofumesate and prodiamine, is unknown. The objectives of this field study, therefore, were to assess the tolerance of `Rebel II' tall fescue (Festuca arundinacea Schreb.), and the fine-leaf fescue species `Reliant' hard fescue (Festuca longifolia Thuill.), `Jamestown II' Chewings fescue (Festuca rubra L. ssp. commutata Gaud.), and `MX 86' blue sheep fescue (Festuca glauca L.) to various rates, combinations, and times of application of ethofumesate and prodiamine. `Rebel II' was most tolerant of ethofumesate; however, sequential rates ≥0.84 + 0.84 kg·ha-1 reduced quality for 1 or more weeks and 2.24 + 2.24 kg·ha-1 caused unacceptable injury. Single applications of ethofumesate at rates of 0.56, 0.84, and 1.12 kg·ha-1, and sequential treatments of 0.56 + 0.56 and 0.84 + 0.84 kg·ha-1 reduced `Reliant' quality temporarily. Sequential treatments of high rates (i.e., 1.12 + 1.12 and 2.24 + 2.24 kg·ha-1), however, significantly reduced `Reliant' cover. `Jamestown II' was very sensitive to ethofumesate, but recovered from single applications of 0.56, 0.84, and 1.12 kg·ha-1; sequential applications (≥0.84 + 0.84 kg·ha-1) caused unacceptable injury, and rates ≥1.12 + 1.12 kg·ha-1 caused significant loss of cover. The cultivar MX 86 tolerated single applications of 0.56 to 2.24 kg·ha-1 of ethofumesate, but sequential treatments generally reduced quality to unacceptable levels. In one study, `Jamestown II' and `MX 86' were more severely injured when ethofumesate (1.12 or 2.24 kg·ha-1) was applied in October rather than in November. The fescues generally best tolerated a single, November application of ethofumesate at ≤1.12 kg·ha-1. Prodiamine (0.73 kg·ha-1) caused only short-term reductions in quality of `Jamestown II', but was generally noninjurious to the other fescues. Ethofumesate tank-mixed with prodiamine (0.84 + 0.36 or 1.12 + 0.73 kg·ha-1) elicited some short-term reduction in quality, but the level of injury was generally acceptable and injured fescues had recovered by spring. Chemical names used: [±]2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate (ethofumesate); N3,N3-di-n-propyl-2,4-dinitro-6-(trifluoromethyl)-m-phenylenediamine (prodiamine); S,S-dimethyl 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-3,5-pyridine-dicarbothioate (dithiopyr).