Sorry to be ill and absent for awhile. I use Dr. Bronner's Liquid Castille soap.
If you use vinegar, Evan, be very careful of the overspray.
If the poison ivy is no longer young and green you can mix the soap and the water with some vinegar an salt but I'll have to locate the proportions. This, however, will kill everything and remain in the soil as well. Don't use it near wells and creeks.
