Case Details
Wild Parsnip.....gone wild
Submitted by Mike Rankin on 9/1/2009
It continues to amaze how fast wild parsnip is spreading. This town road was mowed after the initial flush of WP was headed out (about 2 weeks earlier than the county roads, and the 2nd mowing of the season). Now we see a second strong flush coming-on. Can we really expect road crews to mow for a 3rd time? That will be a tough sell (I think). Interestingly, the county roads mowed 2 weeks later have no regrowth, but the seed from the first flush may have been viable (not sure). Do we know the best mowing strategy? Maybe there isn't one as evidenced by the last picture of WP near the culvert in my front lawn. I "weed whack" that area pretty regularly. I think we might be fighting a losing battle unless mowing occurs frequently (not likely) or a chemical approach is initiated (also not likely).

Wild Parsnip
Wild Parsnip
Wild Parsnip near culvert

See other Weed Control cases
Reply by Mark Renz on 9/1/2009
Mike, I have never researched this, but have heard several testimonials from land managers that state that timely mowing can control wild parsnip. They state that in most years, if wild parsnip is mowed just as it starts to flower, while plants will regrow and flower again, rarely will they produce viable seed. I am sure this will vary a lot by year and location, but when repeated over many years populations can be reduced. success stories I have heard are in the 5 years and more of mowing, and have been areas that typically don't get new seeds imported (by county mowers).

I am not sure what happened in this case, but perhaps the wild parsnip was mowed too early and it had more energy to rebolt, requiring the second mowing. I have seen this with biennial thistles, where when mowed right when they start to flower struggle to regrow, but if mowed at the bolting stage regrow much more rapidly. look (don't touch) to see if seeds are filling or not. With this cool weather hopefully they don't.

We have looked at herbicide options, and have found Ally/Escort or 2,4-D applications are very effective. Plants are most sensitive in the fall, but spring applications in late May can kill adults that will flower and emerged seedlings giving essentially 2 years of control before plants flower again. Seeds don't persist in the soil for more than 5 years, with most depleted in the first couple.

Mark