Asiatic dayflower (Commelina communis) control in Douglas fir

Abstract Asiatic dayflower (Commelina communis L.) is becoming increasingly invasive in Christmas tree plantations in the U.S. Northeast. Response of C. communis to preemergence or postemergence herbicides was evaluated in separate field and greenhouse experiments. The preemergence herbicides consisted of two application rates of flumioxazin (215 and 429 g ai ha–1), hexazinone plus sulfometuron-methyl (316 and 527 g ai ha–1), indaziflam (41 and 82 g ai ha–1), and S-metolachlor (2,136 and 4,272 g ai ha–1). The postemergence herbicides were: bentazon at 1,121 g ai ha–1, clopyralid at 280 g ae ha–1, mesotrione at 526 g ai ha–1, topramezone at 294 g ai ha–1, and triclopyr at 842 g ae ha–1. At 16 wk after treatment, higher rates of flumioxazin (429 g ha–1), hexazinone plus sulfometuron-methyl (527 g ha–1), indaziflam (82 g ha–1), and S-metolachlor (4,272 ha–1) provided 80% to 92% control and reduced C. communis plant density by 84% to 93% compared with the nontreated control. The lower rates of flumioxazin (215 g ha–1), hexazinone plus sulfometuron-methyl (316 g ha–1), and S-metolachlor (2,136 ha–1) gave 65% to 72% control and reduced C. communis plant density by 27% to 75% compared with the nontreated control. The postemergence application of mesotrione at 526 g ha–1, topramezone at 294 g ha–1, and triclopyr at 842 g ha–1 resulted in 76% to 90% control and reduction in dry biomass of 10- to 12-leaf C. communis at 28 d after treatment. Bentazon at 1,121 g ha–1 and clopyralid at 280 g ha–1 applied postemergence were ineffective with <10% control and reduction in C. communis dry biomass. This study showed that C. communis can be managed effectively with currently registered preemergence and postemergence herbicides in Christmas trees.