Tolerance of Hooker's Evening Primrose (Oenothera elata) Transplants to Postemergence Herbicides

Abstract

Greenhouse trials were conducted to determine Hooker's evening primrose transplant tolerance to POST-applied herbicides. Herbicide treatments consisted of glyphosate at 1.68 kg ae ha−1, glufosinate at 0.84 kg ai ha−1, fenoxaprop at 0.10 kg ai ha−1, fluazifop at 0.45 kg ai ha−1+ a nonionic surfactant (NIS) at 0.25% v/v, sulfosulfuron at 0.06 kg ai ha−1+ NIS at 0.25% v/v, quinclorac at 0.42 kg ae ha−1+ methylated seed oil (MSO) at 0.5% v/v, mesotrione at 0.21 kg ai ha−1, and the combination of quinclorac + mecoprop + dicamba at 0.42 + 0.21 + 0.06 kg ae ha−1+ MSO at 0.5% v/v. Fluazifop (14%) and fenoxaprop (19%) treatments did not result in any significant phytotoxicity 7 d after treatment (DAT) compared with the nontreated check. Hooker's evening primrose exhibited 26 to 37% phytotoxicity in response to quinclorac, glyphosate, or sulfosulfuron 7 DAT. Phytotoxicity ≥ 50% was observed for mesotrione, glufosinate, and the combination of quinclorac + mecoprop + dicamba 7 DAT. Phytotoxicity increased for all treatments 28 DAT. Fluazifop (21%) was the only treatment that did not exhibit phytotoxicity symptoms different from the nontreated check 28 DAT. Hooker's evening primrose exhibited 31 to 40% phytotoxicity with applications of fenoxaprop, glyphosate, or glufosinate 28 DAT. Phytotoxicity was ≥ 58% with all other treatments 28 DAT. Fluazifop exhibited similar above-ground (12.4 g) and below-ground (16.4 g) biomass as the nontreated check (10.8 and 14.7 g, respectively) 28 DAT. All other treatments resulted in 1.6 to 5 g of above-ground biomass and 0.8 to 4.3 g of below-ground biomass 28 DAT. Fluazifop (24.3) and fenoxaprop (18.8) applications resulted in a plant growth index (PGI) that was not significantly different from the nontreated check (24.7) 28 DAT. A PGI ≤ 16.2 was observed for all other treatments 28 DAT.