Roundup

Boiling water if practical regarding size of infestation and distance from stove - and gracefulness/balance of the person who will carry it. Only needs to go on the roots.

I've actually had to hire somebody who isn't allergic to completely dig up the poison ivy around my place. What they did with it afterwards, I don't know. They carried it off with them. I haven't had any problems since. But please, no body make the mistake of thinking you can burn the stuff. The smoke will carry the "poison" & still cause you to break out. I can't tell you how many times my dad did this.

Consider using an herbicide like Vinex. if the plant is large or growing up a tree or fence. The application is actually quite minimal, coat the bark at the stem at the base of the plant with the brush which is permanently attached to the bottle of Vinex.