title: Reduced absorption of glyphosate and decreased translocation of dicamba contribute to poor control of kochia (Kochia scoparia) at high temperature.
abstract: BACKGROUND
  Plant growth temperature is one of the important factors that can influence postemergent herbicide efficacy and impact weed control. Control of kochia (Kochia scoparia), a major broadleaf weed throughout the North American Great Plains, often is unsatisfactory when either glyphosate or dicamba are applied on hot summer days. We tested effects of plant growth temperature on glyphosate and dicamba phytotoxicity on two Kansas kochia populations (P1 and P2) grown under the following three day/night (d/n) temperature regimes: T1, 17.5/7.5°C; T2, 25/15°C; and T3, 32.5/22.5°C.
  
  
  RESULTS
  Visual injury and above-ground dry biomass data from herbicide dose-response experiments indicated greater susceptibility to both glyphosate and dicamba when kochia was grown under the two cooler temperature regimes, i.e. T1 and T2. At T1, the ED50of P1 and P2 kochia were 39 and 36 g ha-1of glyphosate and 52 and 105 g ha-1of dicamba, respectively. In comparison, at T3 the ED50increased to 173 and 186 g ha-1for glyphosate and 106 and 410 g ha-1for dicamba, respectively, for P1 and P2. We also investigated the physiological basis of decreased glyphosate and dicamba efficacy under elevated temperatures. Kochia absorbed more glyphosate at T1 and T2 compared to T3. Conversely, there was more dicamba translocated towards meristems at T1 and T2, compared to T3.
  
  
  CONCLUSIONS
  Reduced efficacy of dicamba or glyphosate to control kochia under elevated temperatures can be attributed to decreased absorption and translocation of glyphosate and dicamba, respectively. Therefore, it is recommended to apply glyphosate or dicamba when the temperature is low (e.g. d/n temperature at 25/15°C) and seedlings are small (less than 12 cm) to maximize kochia control. © 2016 Society of Chemical Industry.
authors.affiliation: Department of Agronomy, Kansas State University, 2004 Throckmorton Plant Sciences Center, 1712 Claflin Road, Manhattan, KS, USA.
authors.forename: Junjun
authors.initials: J
authors.lastname: Ou
authors.affiliation: Agricultural Research Center-Hays, Kansas State University, 1232 240th Avenue, Hays, KS, USA.
authors.forename: Phillip W
authors.initials: PW
authors.lastname: Stahlman
authors.affiliation: Department of Agronomy, Kansas State University, 2004 Throckmorton Plant Sciences Center, 1712 Claflin Road, Manhattan, KS, USA.
authors.forename: Mithila
authors.initials: M
authors.lastname: Jugulam
mesh_terms: D027467:Bassia scoparia / Q000187:drug effects*; D003996:Dicamba / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D053209:Herbicide Resistance; D006540:Herbicides / Q000494:pharmacology*; D006358:Hot Temperature; D058728:Weed Control; D000097797:Glyphosate
chemical_list: D003996:Dicamba; D005998:Glycine; D006540:Herbicides; D000097797:Glyphosate
keywords: dicamba; glyphosate; growth temperature; kochia