How do I control poison hemlock and wild parsnip?

Question: 

How do I control poison hemlock and wild parsnip?

Answer: 

Control of wild parsnip (Pastinaca sativa) and poison hemlock (Conium maculatum) is the same.  Safely removing these weeds from the landscape is important as both species can be toxic to humans and animals.  

Protect Yourself

Control of this weed takes special care.  It is important to reduce contact with these species by doing things like wearing good waterproof gloves, long sleeves & pants, protective eyewear, and closed-toed shoes.

Wild parsnip plant parts contain a substance called psoralen, which can cause skin reddening, rashes, and blisters when sap or juice from the plant gets on the skin and the skin is exposed to sunlight.  All parts of the poison hemlock plant are highly toxic to humans and animals and may result in death if ingested. Because plants look similar to edible species of the carrot family, occasionally plant parts are mistakenly ingested.

Management Options

These weeds persist in the landscape through the spread of seed.  Elimination of seed production and spread is the goal for managing these weeds.

Discourage Growth and Development

The best defense against these weeds is to promote garden spaces that do not favor their growth.  Wild parsnip and poison hemlock typically inhabit roadsides, disturbed sites, pastures, field edges, or natural areas. Maintaining good plant cover on the soil to compete with these species helps insure they never germinate or take root.

Pulling & Digging

Mechanical removal of flowers and seeds by carefully hand pulling or digging the root crown can be effective control methods.  This is best done in the summer before plants are large and flowering.  Non-flowering crowns can be dug any time of the year when observed.  The goal is to prevent seed production. Since flowering does not occur all at once, the area must be monitored for several weeks. If people, pets, or livestock could come into contact with the plant material after digging, carefully bag the plant material and toss it in the trash.

Mowing & Cutting

Repeated mowing or cutting flower stalks can help reduce the occurrence of flowering and seed set, but does not eliminate the rosette and has the high potential of splattering the sap of wild parsnip on the skin causing rashes and blisters.  For large infestations, this can be an effective way to reduce seed set, which is a primary goal, but it must be done with care.

Herbicides

Both species can be controlled with spot applications of herbicides.  Apply a non-selective herbicide, such as glyphosate, in early spring or late fall. Broadleaf herbicides like 2,4-D or dicamba can also be applied in early spring or late summer/fall.  Avoid contacting desirable plants with these herbicides. Monitor the area frequently over the entire growing season.  Additional herbicide applications or mechanical control measures may be necessary later in the season and over the next couple of years to control newly emerging plants.

Identification Resources

Information on how to identify these species of weed can be found in the links below:

 

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