Metamifop Rates, Application Timings, and Broadleaf Herbicide Admixtures Affect Smooth Crabgrass Control in Turf

Abstract

Metamifop is an aryloxyphenoxypropionate herbicide under evaluation in the United States for annual grass control in cool-season turfgrasses. Insufficient information is available on the most effective metamifop application timings and mixtures for POST smooth crabgrass control. Field trials conducted in Blacksburg, VA, evaluated metamifop for smooth crabgrass control in existing stands of perennial ryegrass, Kentucky bluegrass, and tall fescue at three rates compared to fenoxaprop, metamifop applied twice at three application intervals, and metamifop in combination with the broadleaf herbicides carfentrazone, 2,4-D plus dicamba plus mecoprop (DDM), and mesotrione. Smooth crabgrass control was equivalent with metamifop at 400 g ai ha−1and fenoxaprop at 195 g ai ha−1. Smooth crabgrass cover was 2% or less, 12 wk after initial treatment, when treated twice with metamifop (300 g ha−1) at a 3-, 6-, or 8-wk interval and significantly better than metamifop applied once. Smooth crabgrass cover was significantly greater at every assessment date in plots treated with metamifop plus DDM than all other metamifop plus broadleaf herbicide admixtures. Metamifop did not appear to significantly injure any turfgrass in these studies, but conclusions about metamifop safety to cool-season turfgrasses cannot be made from these studies due to nonreplication of turfgrass species. According to these data, metamifop is an effective herbicide for controlling smooth crabgrass in cool-season turfgrasses when applied once at 300 or 400 g ha−1or twice at a 3-, 6-, or 8-wk interval. Although metamifop continues to control smooth crabgrass when added to some broadleaf herbicides, smooth crabgrass control was reduced when metamifop was combined with DDM.