Remedy applied basal will work. 25% Remedy in 75% diesel or basal oil. I like to do it in dead of winter. you apply to bark 15 to 20 inches from base up.
Wouldn't girddling the tree and spraying pathway into the cut also kill it. Pathway is available in small quantities and easily found. This has done a great job on most trees on my farm that where removed in the name of TSI. Uven the maple that got spray and griddled three time finally bite the dust (a strong wind blow it over).
