Answer: Unfortunately, there is no plant that can outcompete the poison ivy. You might be able to smother at least some of it by cutting it off at ground level or digging out what you can, then covering the root area with heavy cardboard or numerous sheets of newspaper, then topping that off with a heavy layer of organic mulch. If it manages to come up through that, cut it off again, then replace the covering. Eventually the root reserves should become exhausted.
There are some new, soap-based herbicides that are considered quite environmentally friendly and safe to use. Avoid using a flame weeder, however, since the smoke from burning poison ivy can be extremely irritating to lungs.
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