This plant is considered very invasive and local counties have taken to spraying chemicals to eradicate it. However, their concern is not that it is invasive, per se, but that if people break off leaves or stems and get the plant juice on their skin and then go out in the sun, they can have a relatively painful photo-dermatitis reaction. But you have to get the juice on your skin and you have to stand in the sun! Over the years, I've stood amidst stands of this plant, brushed past it, handled it constantly and never experienced any reaction because I'm careful not to pick the flowerhead, break off the leaves, etc. There is a biocontrol agent, the parsnip webworm, larvae of a moth, http://www.pbase.com/laroseforest/image/163629656, but spraying and cutting down the plant and thus killing the larvae is preventing the insect from making much inroad. Meantime the spraying kills every other plant, native and non-native growing near the parsnip and the wild parsnip emerges again the following year.