Earth Matters by Jacqueline Milner – The Challenges of Wild Parsnip – April 12, 2011 – Cornwall Ontario

Cornwall ON – As there has been much debate lately about wild parsnip and how to control it; it might be helpful to reshare information on what the plant looks like, its challenges and how it can be safely managed.  We have discussed management of this plant before however being aware that early season cutting of this plant is key, a reminder of this information early this spring could prove beneficial to all. 

The challenges with wild parsnip
Wild parsnip (also known as poison parsnip) has a nasty reputation for causing “burn like blisters” on the skin wherever liquid from the broken parts of the plants leave their liquid chemicals called psoralens which triggers phytophotodermatitis. These blisters only develop 24 to 48 hours after exposure. Phytophotodermatitis is caused by the sun’s UV rays activating the psoralens that are absorbed into the skin causing burns (blisters) on the skin as a reaction. Sweat and humidity help speed the absorption of psoralens into the skin.  Each plant produces hundreds of seeds which can over populate and crowd out other species in a short period of time. Lastly, the seed may remain viable in the ground for up to five years.

Controlling the growth of Wild Parsnip
Vigilance and regular mowing at the appropriate time is required to eradicate this species from a growing area.  Before resorting to the use of herbicides, it is of benefit to question whether there are more effective and environmentally friendly ways of dealing with the wild parsnip invasion.  Spraying does not affect the seed.  The plants can develop resistance to the chemicals being sprayed and can affect other beneficial plants, insects and animals. Wild parsnip in its first year of growth produces no flowers and just shows as a tuft of basal leaves, as shown in the image below.

In the second year, the wild parsnip goes into bud generally in July. They then go into flower (as indicated in title image), producing seed (as indicated in photo below) in midsummer to early fall.  Plants can grow to over 5 feet tall.  After producing seeds, the plants die. The best way to control the spread of wild parsnip and keep it at bay is to mow or “weed eat” it just when the buds are beginning to show (somewhere between end of June and beginning of July) depending on the geographical location and climate. To mow or use the weed eater later in the season actually may contribute to spreading the seeds and therefore increase the spread of the wild parsnip population.

Of Special note
Should mowing or weed eating take place after the plant has already flowered, the flowers will continue to grow and produce mature seed.  Mowing before the plants flower is vital. For smaller isolated patches of wild parsnip, you may break the tap root with a shovel or spade in order to control these plants. Caution: Always make sure to wear clothing and gloves that provide protection from contact with these plants, especially in sunlight. If you have come in contact with wild parsnip wash and flush your skin and that of any animal with you with water immediately.

Key points to remember.
1.  Keep the skin covered when dealing with this plant.
2.  After cutting or contact insure clothing is immediately removed and washed insuring no further skin contact is made.  If the juices of the plant make skin contact flush area immediately with water.
3. The best method for the average homeowner to eliminate/control the plant is to cut before flowering.

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