By Bill Kleiman, The Nature Conservancy at Nachusa Grasslands
Pastinaca sativa, wild parsnip lives two years, with flower and seed set on year two. Every June you will find us mowing it somewhere on the preserve, as this is when they are in full flower. We also use our weed spades to cut the root which looks like a carrot. Before the flower stalk bolts a broadleaf herbicide is effective.
Parsnip does not compete well in prairie plantings or prairie remnants, except where the vegetation has been disturbed by some past issue, like brush encroachment. Parsnip does well in low competition areas where past disturbance has left a simple plant community. We mowed a bush honeysuckle thicket several years previously and it filled with wild parsnip a few years later. I sprayed a pasture to reduce brush and a few years later there was the parsnip.
There are various weeds we put some effort into in case their small populations might increase if left alone. Weeds like parsnip, king devil, butter and eggs. You may have such a list. Then there are weeds that are everywhere, like the exotic cool season grasses, so we shrug our shoulders and don’t attempt to control them.
Our resources are limited so we manage what we need to, and not more.
Here is a link to some resources on invasive weeds: