...makes a poison ivy spray that you have to spray onto the leaves, preferably on a nice day with no rain on the forecast. We've used it to good effect in my garden. I blame birds who eat the seeds and then leave droppings in my garden.
Perhaps ask the park administrators (if any) what they recommend and how can you help? I think a lot of parks would appreciate this effort if they knew someone responsible was doing it voluntarily.
You also want to do it when there is little or preferably no wind. But it works.