Virginia buttonweed (Diodia virginiana) control with pyridine herbicides

Field experiments were conducted to evaluate pyridine herbicides for Virgin ia buttonweed control and turfgrass tolerance. Treatments included clopyral id 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 con trolled Virginia buttonweed 80% or greater through 10 wk after treatment. A second experiment evaluated 280 g/ha clopyralid or 140 g/ha fluroxypyr alo ne or in combination with 0.25 or 0.50% (v/v) nonionic surfactant, compared to 280 g/ha dicamba or 1,120 g/ma 2,4-D alone or in combination with nonio nic surfactant. The addition of nonionic surfactant to clopyralid or flurox ypyr did not increase Virginia buttonweed control. Fluroxypyr at 280 g/ha a nd 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 fl uroxypyr 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.