Abstract: Field experiments were conducted to evaluate pyridine herbicides for Virginia buttonweed control and turfgrass tolerance. Treatments included clopyralid and fluroxypyr applied at 35, 70, 140, 280, and 560 g ae/ha, compared to a three-way combination of 2,4-D plus dichlorprop plus dicamba (840 840 210 g ae/ha, respectively). Fluroxypyr applied at 140 g/ha or greater controlled Virginia buttonweed 80% or greater through 10 wk after treatment. A second experiment evaluated 280 g/ha clopyralid or 140 g/ha fluroxypyr alone or in combination with 0.25 or 0.50% (v/v) nonionic surfactant, compared to 280 g/ha dicamba or 1,120 g/ha 2,4-D alone or in combination with nonionic surfactant. The addition of nonionic surfactant to clopyralid or fluroxypyr did not increase Virginia buttonweed control. Fluroxypyr at 280 g/ha and higher produced 22 to 53% injury to bermudagrasses 2 wk after treatment. Common centipedegrass was injured through 3 wk after treatment with 4,470 g/ha fluroxypyr or greater. Zoysiagrass exhibited injury with 4,470 g/ha fluroxypyr at 2 wk after treatment; however, injury was less than 8% at 3 wk. Common St. Augustinegrass was severely injured with 2,235 g/ha or greater fluroxypyr through 7 wk after treatment. Clopyralid did not cause injury to any turfgrass species.
Nomenclature: Clopyralid; dicamba; dichlorprop; fluroxypyr; 2,4-D; common bermudagrass, Cynodon dactylon (L.) Pers. #3 CYNDA; common centipedegrass, Eremochloa ophiuroides (Munro) Hack. # ERLOP; common St. Augustinegrass, Stenotaphrum secundatum (Walt.) Ktze. # STPSE; hybrid bermudagrass, Cynodon dactylon × C. transvaalensis Burtt-Davy ‘Tifway’, ‘Tifgreen’; Virginia buttonweed, Diodia virginiana L. # DIQVI; Zoysiagrass, Zoysia japonica Steud. ‘Meyer’ # ZOYMA.c
Additional index words: CYNDA, DIQVI, ERLOP, STPSE, ZOYMA.
Abbreviations: MHE, methylheptyl ester.