Abstract: Several commercial and experimental adjuvants were evaluated for efficacy in enhancing activity and selectivity of quinclorac in two cultivars of canola and four turfgrass species. Weed species investigated included cleavers, annual sowthistle, large crabgrass, and goosegrass. Turfgrass species evaluated included Kentucky bluegrass, perennial ryegrass, tall fescue, and creeping bentgrass. A variety of adjuvant types were selected, such as a methylated seed oil (Sunit II), a petroleum-based crop oil concentrate, the silicone-based Sylgard 309, a cationic fatty amine ethoxylate surfactant (Frigate), and modified crop oils (Dash and Merge). Adjuvant efficacy was evaluated by calculating the quinclorac rate required to reduce plant growth 50% (GR50) based on rates applied at 0, 15.6, 31.2, 62.5, and 125 g ai/ha. For goosegrass, quinclorac rates evaluated were increased to 250, 500, 1,000, and 2,000 g ai/ha. All evaluated adjuvants provided similar enhancement of control for cleavers and annual sowthistle. Sylgard 309 was the least effective adjuvant for control of large crabgrass. Goosegrass was tolerant to quinclorac across the evaluated rate range regardless of adjuvant; therefore, GR50 values could not be determined. None of the adjuvants alone caused phytotoxicity to canola or any turfgrass species.
Nomenclature: Quinclorac; annual sowthistle, Sonchus oleraceus L. #3 SONOL; cleavers, Galium aparine L. # GALAP; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; canola, Brassica napus L. ‘Garrison’, ‘Goldrush’; creeping bentgrass, Agrostis palustris (L.) Huds.; Kentucky bluegrass, Poa pratensis L.; perennial ryegrass, Lolium perenne L.; tall fescue, Festuca arundinacea (L.) Schreb.
Abbreviations: GR50, herbicide rate required to reduce growth 50%; PPFD, photosynthetic photon flux density.
