Wild Parsnip: Look But Don’t Touch
Author Joe Boggs
Published on April 4, 2023
The acute skin reaction to the wild parsnip sap means this non-native invasive weed should not be allowed to grow where it can be easily contacted by people. Landscape managers and gardeners should also exercise extreme caution around this non-native invasive plant.
The safest approach to controlling this invasive weed is to use herbicides. Of course, as always, read and follow label directions paying close attention to recommended rates and whether or not surfactants are recommended to enhance herbicide efficacy.
Fortunately, wild parsnip is susceptible to a wide range of selective and non-selective postemergent herbicides. Non-selective herbicides with the active ingredients glyphosate (e.g., Roundup) or pelargonic acid (e.g., Scythe) are effective but can also eliminate plants that compete with wild parsnip.
Herbicidal openings produced by non-selective herbicides provide perfect opportunities for wild parsnip to spring forth from previously deposited seed. Thus, it's important to have a plan for establishing competitive plants such as over-seeding with grasses (family Poaceae). Grasses are effective competitors against wild parsnip and a range of selective post-emergent herbicides can be used that will preserve grasses but kill the poison hemlock. These include clopyralid (e.g., Transline), metsulfuron (e.g., Escort XP), triclopyr (e.g., Triclopyr 4), and products that contain a combination of 2,4-D, dicamba, mecoprop, and dichlorprop.
The graphic illustrates that the best time to make herbicide applications is just after last season’s rosettes are starting to bolt but before flowers are produced. Seeds have also germinated by this time. Killing the seedlings will reduce next year's rosettes and killing the bolting rosettes will prevent seed production later this season. Eliminating these plants can significantly reduce infestations. Note that mowing is not included in the graphic as a viable management option.