Question: If the state and county are so concerned about wild parsnip, why aren’t they out spraying it? The ditches and county roads are full of it.1
Answer: I would say the primary problem with managing wild parsnip is that it is naturalized and found everywhere in Iowa with suitable habitat. One of ISU’s early botanists published a book2 in 1926 indicating that wild parsnip was in every county. The foundation of invasive species management is early detection and rapid response – we obviously missed the boat with wild parsnip.
Due to limited budgets, most counties and the state only attempt to control roadside weeds that are classified as noxious (wild parsnip is not listed). This contrasts to programs from 40 to 50 years ago where nearly every roadside was mowed or sprayed at least once a year. These programs reduced weed problems, but were very expensive and not very environmentally friendly. Mowing of roadsides is not allowed until July 15 in order to protect nesting bird habitat (there are exemptions). Unfortunately, mowing after mid-July minimizes the effectiveness of this tactic in controlling wild parsnip since viable seed will have already been produced.
Most Iowa counties have Integrated Roadside Vegetation Management programs (IRVM). Their goal is to establish habitat (typically native prairie species) along roadsides that is less prone to invasion by weedy species. This approach can be effective, but budgets restrict the amount of roadside that can be converted to more resilient vegetation. IRVM also uses spot applications of herbicides to control weeds rather than broadcast spraying of the entire roadside. But as mentioned earlier, spraying usually focuses on Iowa noxious weeds.
I think efforts should be made to control wild parsnip in parks and other areas commonly used for recreation or other purposes. But I think there are better things to do with the limited resources available than attempt to control wild parsnip in roadsides. I’ve spent a lot of time surveying roadside vegetation and don’t find it too difficult to avoid the plant (but perhaps my skin is so sun damaged already that I’m not sensitive to the photosensitizing compounds in wild parsnip). I think it is unlikely that we will see an increased effort at managing wild parsnip in most areas, thus it is important for people who utilize areas suitable for this plant to learn how to identify and avoid the plant.
1This is the response I sent to a reporter who received the question from a reader.
2Pammel, L.H. 1926. The weed flora of Iowa.