The wet blade system (WBS) directs chemicals to the cut surface during mowing thus eliminating the need for a separate application. Applying chemical only to cut plants reduces the likelihood of herbicide movement compared to broadcast application. A field study was conducted to compare WBS to foliar spray applications of quinclorac, fenoxaprop, and MSMA for postemergence large crabgrass (Digitaria sanguinalis (L.) Scop.) control and Kentucky bluegrass (Poa pratensis L.) tolerance. The study was initiated at Blacksburg, VA on August 20, 2002 in established ‘Midnight’ Kentucky bluegrass turf infested with large crabgrass. The experimental design was a randomized complete block with treatments replicated three times in a split-plot design. Main plots had four levels consisting of quinclorac at 0.56 lb ai/A and 1.13 lb ai/A, fenoxaprop at 0.07 lb ai/A, and MSMA at 1.25 lb ai/A. Subplots consisted of either foliar spray or WBS application methods. Application volumes were 1 and 30 gal/A for WBS and foliar spray, respectively. Large crabgrass control was visually estimated at 1, 2, and 4 weeks after treatment (WAT) as a percentage compared to the nontreated control.
Fenoxaprop controlled crabgrass significantly more with broadcast application (85%) compared to WBS (35%) at 4 WAT. Quinclorac and MSMA controlled crabgrass less than 40% regardless of application method. All treatments injured Kentucky bluegrass injury 13% or less 4 WAT. Suboptimal environmental conditions slowed turf and weed growth and likely influenced herbicide efficacy. Results suggest herbicides applied via foliar spray may produce visual symptoms of control faster than the WBS. Under drought conditions, fenoxaprop controls crabgrass better when applied as a foliar spray compared to the WBS. However, effects of WBS-applied fenoxaprop, quinclorac, and MSMA on long-term large crabgrass control are inconclusive due to inherent environmental conditions of this study.