Preemergent Control of Crabgrass Using Vexis(TM) Pyrimisulfan and Vexis(TM) with Penoxsulam.

A new active ingredient, pyrimisulfan, is entering the turf industry under the branded named of Vexis™. Pyrimisulfan is reported to inhibit acetolactate synthase (ALS) in sensitive plants, which inhibits the biosynthesis of the brand-chain amino acids valine, leucine and isoleucine. There are different formulations of Vexis™ for use on cool- and warm-season turf, therefore the objectives of this project were to evaluate these Vexis^TM formlations for their efficacy in control of crabgrass (Digitaria spp.) on bermudagrass (Cynodon dactylon (L.) Pers.) and tall fescue (Festuca arundinacea Screb.) turfs when applied as a preemergence herbicide. Two experiments were conducted on established bermudagrass and tall fescue turf following overseeding with crabgrass seed. Treatments included pyrimisulfan alone or pyrimisulfan plus penoxsulam, another ALS inhibitor, at different rates. Treatments were applied to individual plots measuring 1.5 m x 1.5 m, and arranged in a randomized complete block design with four replications. Granular treatments were applied with shaker bottles, and sprayable treatments were applied using a CO₂ pressurized backpack sprayer with Tee Jet XR8004 flat fan nozzles calibrated to 374 L/ha. On bermudagrass, crabgrass coverage reached 15% at 4 weeks after initial treatment (WAIT), while all treated plots, including the granular form of pyrimisulfan-containing treatments, resulted in 5% crabgrass. A similar trend was found 6 WAIT, and no differences were found between pyrimisulfan-containing treatments and the commercial preemergence herbicide, dithiopyr. On tall fescue, similar results were found except one Vexis^TM premix formulated as a liquid suspension showed minor and temporary discoloration to tall fescue plant following application. More details will be discussed in the presentation.