Chemical Mixtures for Control of Winged Elm

Various growth regulators, carrier systems, and ammonium thiocyanate (NH4SCN) additions in combination with herbicide mixtures were evaluated for their foliar phytotoxicity to winged elm (Ulmus alataMichx.). Silvex [2-(2,4,5-trichlorophenoxy)propionic acid] and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] were more effective than the dichlorophenoxy herbicides. Additions of NH4SCN to the ester of 2,4,5-T consistently increased control. Picloram (4-amino-3,5,6-trichloropicolinic acid) was the most effective herbicide for killing the trees, and in mixtures with the phenoxy herbicides consistently produced good tree kill. No increase in 2,4,5-T activity could be attributed to additions of growth regulators, concentrated nutrient solutions, or to type of carrier system used.