TANK MIXTURES AND APPLICATION INTERVALS FOR SMOOTH CRABGRASS CONTROL WITH METAMIFOP. M.C. Cox* and S. Askew, Virginia Tech, Blacksburg, VA (25)
Metamifop is a new herbicide under development in US markets by Summit Agro. Metamifop controls annual grasses without injuring desirable cool season turfgrass species. Already marketed in 9 other Asian and 6 Middle Eastern countries as a postemergent annual grass herbicide in cereal crops and rice, metamifop shows great potential for future expansion to Japan and North America. Metamifop inhibits acetyl-CoA carboxylase (ACCase) which is the enzyme that catalyzes the first step in fatty acid synthesis. This enzyme inhibition prevents production of phospholipids which are the building blocks for new membranes and cell growth. Cool-season turfgrasses are said to gain tolerance to metamifop via an altered ACCase binding site, which makes this herbicide unique among other ACCase inhibitors that rely on rapid metabolism for turf safety. Field trials conducted in Blacksburg, VA evaluated the use of metamifop in application intervals and metamifop in conjunction with the broadleaf herbicides 2,4-D + dicamba + MCPP (Trimec Classic, PBI Gordon Corporation), carfentrazone (Quicksilver, FMC Corporation), and mesotrione (Tenacity, Syngenta) for control of smooth crabgrass (Digitaria ischaemum). The experiments were implemented in Kentucky bluegrass (Poa pratensis) and perennial ryegrass (Lolium perenne) maintained at fairway height. Treatments for the metamifop interval trial consisted of metamifop applied at 300 g ai/ha alone or followed by an additional application at 3, 6, or 8 weeks after initial application. Treatments for the metamifop/broadleaf herbicides combination trial consisted of metamifop applied at 300 g ai/ha alone, Trimec Classic alone at 4.68 L/ha, Quicksilver alone at 0.15 L/ha, Tenacity alone at 0.58 L/ha, metamifop + Trimec (same rates as single treatments), metamifop + Quicksilver, and metamifop + Tenacity. A nontreated check was included in all trials for comparison. When applied alone at 3, 6, or 8 week intervals, metamifop controlled smooth crabgrass 88 to 98% and significantly better than metamifop applied once. These treatments did not injure Kentucky bluegrass or perennial ryegrass at any time during the study. Applications of metamifop alone, metamifop + Quicksilver, and metamifop + Tenacity controlled smooth crabgrass 65-90% initially and 55-63% 12 weeks after treatment (WAT). Metamifop + Trimec only controlled crabgrass 10% initially and 6% 12 WAT, suggesting a possible antagonism between the two herbicides. Likewise, Trimec alone controlled dandelion (Taraxacum officinale) 90% 12 WAT and significantly better than metamifop + Trimec at 57% control 12 WAT. Nevertheless, metamifop + Trimec controlled white clover (Trifolium repens) 97% 12 WAT and significantly better than all other treatments. According to these data, metamifop is an effective herbicide for controlling smooth crabgrass in cool season turfgrasses when applied twice at 3, 6, or 8 week intervals. In addition, although metamifop may have safety when added to some broadleaf herbicides, an antagonistic response resulted when it was combined with Trimec Classic as a crabgrass/broadleaf herbicide tank mix. 2,4-D and MCPP, two active ingredients in Trimec Classic, are also known antagonist of other ACCase inhibiting herbicides such as fenoxaprop.