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If so, what timeframe?
Roundup alone is not terribly effective on poison ivy because of the
oiliness of the leaves. You need a good surfactant mixed with the
roundup. Some people use a bit of dish soap in the mix - some a few
tablespoons of diesel fuel. I know the diesel fuel works. Generally
knocks it back pretty good in about 3 or 4 days.

roundup mixed 50 / 50 with poision ivy killer, it will be dying by the next morning, its amazingly effective