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It may come down to rototilling the entire back yard and starting over. Beside wild parsnip there is an abundance of poison ivy. It would give me a chance to level the ground as it is very uneven.

It sounds like something you should do as soon as possible

The poison ivy problem is going to remain a problem as they grow in the roots of the cedar hedges belonging to my neighbors. Short of killing off their hedges (to which I am sure they would object) the most I can do is reduce what is growing in my yard.