Seedling Tolerance of Cool-season Turfgrasses to Metamifop

Abstract

Grassy weeds may reduce cool-season turfgrass establishment after seeding and herbicide use is often warranted. Field experiments were conducted to evaluate the tolerance of creeping bentgrass (Agrostis stolonifera L.), perennial ryegrass (Lolium perenne L.), and tall fescue (Festuca arundinacea Schreb.) to fenoxaprop and metamifop applications at 1, 2, 3, or 4 weeks after seeding (WAS). Creeping bentgrass groundcover was reduced from 34% to 71% at 8 WAS from the nontreated by fenoxaprop at 50 g a.i./ha and metamifop at 400 and 800 g a.i./ha at all application timings. Metamifop at 200 g·ha−1 reduced creeping bentgrass cover 10% to 18% from the nontreated at 8 WAS when applied 1, 2, or 3 WAS, but treatments at 4 WAS did not reduce cover. Perennial ryegrass treated with fenoxaprop and metamifop at 800 g·ha−1 at 1 WAS had cover reduced from the nontreated on two and one dates, respectively, whereas tall fescue cover was never reduced greater than 5% from the nontreated. Results suggest applications to creeping bentgrass should be delayed greater than 4 WAS for fenoxaprop at 50 g·ha−1, greater than 4 WAS for metamifop at 400 and 800 g·ha−1, and 3 WAS for metamifop at 200 g·ha−1. Additionally, fenoxaprop applications should be delayed 2 WAS for perennial ryegrass and tall fescue, whereas metamifop could be safely applied at all rates at 1 WAS.