Time of Application Influences Translocation of Auxinic Herbicides in Palmer Amaranth (Amaranthus palmeri). Issue 1 (22nd August 2017)

• Record Type: Journal Article
• Authors: Johnston, Christopher R.; Eure, Peter M.; Grey, Timothy L.; Culpepper, A. Stanley; Vencill, William K.
• Is Part Of: Weed science. Volume 66: Issue 1(2018)
• Page Start: 4
• Page End: 14
• Publication Date: 2017-08-22
• Subjects: 2, 4-D, -- 5-[N-(3, 4-dimethoxyphenylethyl)methylamino]-2-(3, 4-dimethoxyphenyl)-2-isopropylvaleronitrile hydrochloride, -- dicamba, -- Palmer amaranth, Amaranthus palmeri S. Wats.; Auxin transport inhibitor, -- herbicide resistance, -- radiolabeled herbicide; 632.505
• DOI: 10.1017/wsc.2017.36
• Languages: English
• ISSNs: 0043-1745

Abstract

Abstract : The efficacy of WSSA Group 4 herbicides has been reported to vary with dependence on the time of day the application is made, which may affect the value of this mechanism of action as a control option and resistance management tool for Palmer amaranth. The objectives of this research were to evaluate the effect of time of day for application on 2, 4-D and dicamba translocation and whether or not altering translocation affected any existing variation in phytotoxicity seen across application time of day. Maximum translocation (Tmax ) of [ 14 C]2, 4-D and [ 14 C]dicamba out of the treated leaf was significantly increased 52% and 29% to 34% in one of two repeated experiments for each herbicide, respectively, with application at 7:00 AM compared with applications at 2:00 PM and/or 12:00 AM. Applications at 7:00 AM increased [ 14 C]2, 4-D distribution to roots and increased [ 14 C]dicamba distribution above the treated leaf compared with other application timings. In phytotoxicity experiments, dicamba application at 8 h after exposure to darkness (HAED) resulted in significantly lower dry root biomass than dicamba application at 8 h after exposure to light (HAEL). Contrasts indicated that injury resulting from dicamba application at 8 HAEL, corresponding to midday, was significantly reduced with a root treatment of 5-[ N -(3, 4-dimethoxyphenylethyl)methylamino]-2-(3, 4-dimethoxyphenyl)-2-isopropylvaleronitrile hydrochloride (verapamil) compared with injury observed with dicamba application and a root treatment of verapamil at 8 HAED, which corresponded to dawn. Overall, time of application appears to potentially influence translocation of 2, 4-D and dicamba. Furthermore, inhibition of translocation appears to somewhat influence variation in phytotoxicity across times of application. Therefore, translocation may be involved in the varying efficacy of WSSA Group 4 herbicides due to application time of day, which has implications for the use of this mechanism of action for effective control and resistance management of Palmer amaranth.