This is an old post, but still, everyone comes across this three leaf tormenter sooner or later. We have it all over camp, especially in the natural wooded areas.
Herbcides can work, but results vary widely by product, season and weather conditions. My experience is that it works best if applied when conditions are hot and dry (mid-sumnmer). Otherwise it seems to just slow it down for a while.
The only sure method I have found is by digging it up roots and all. Yikes! Sounds pretty dangerous eh? Well, being immune does help. If not, you have to take meaningful steps to protect yourself.
Long shirts, gloves, creams (Ivy Block), hat, etc. all help to prevent the oil from contacting your skin directly. Just don't forget to isolate the clothing and tools later because they may still have oil on them. (my dear wife got it one time from just putting my jeans into the wash)
The areas I have cleared by digging have remained forever clear.
Also, once immune not ALWAYS immune. That can change over the years and simply because of a person's immune system. I take every precaution and wash up thoroughly afterwards, just to be on the safe side.
