Giant Hogweed: Horror Flick for the Summer Landscape

By Rebecca Finneran

Michigan State University Extension

Giant hogweed may look like a beautiful architectural addition to the landscape but this dramatic perennial plant also has a sinister side. As its Latin name implies Heracleum mantegazzianum looks a little like Hercules when it reaches its full height of 6- to 12-feet in Michigan.

With a chunky, greenish-purple stem and platter-sized, deeply dissected foliage, giant hogweed was introduced from Eurasia by plant collectors in the early 1900s for arboretums and gardens. Abundant seeds are produced from frothy, white blooms similar to Queen Anne’s lace and are held on strong stalks, well above the foliage. Its persistent biology coupled with prolific seed production allowed this villain to quickly escape and establish itself in moist soils along roadsides and stream banks. It easily moved towards Michigan from the East Coast through Pennsylvania.

The sinister side of giant hogweed is unveiled when unknowing gardeners or landscape managers come into contact with the seed, foliage and stems, exposing themselves to the dangerous sap. Classified along with the lowly carrot, this family also includes Queen Anne’s lace and parsley but it contains toxins that can cause severe skin and eye irritation. If you ever have experienced the effects of poison ivy, this is a hundred times worse. Skin contact when exposed to sunlight, “activates” the dermatitis reaction causing it to create painful blisters. Contact with eyes can cause temporary or even permanent blindness, and skin contact may leave long-lasting scars.

Hazardous plant

Giant hogweed made it to the USDA dangerous noxious weed list and has been scouted for in Michigan since 1998. With recent media attention, folks are on the lookout for the plant and are encouraged not to touch or try to remove it without proper protection. USDA recommends never touching the plant with your bare hands. Remember that the sap can persist on mowers, string trimmers, tools and gloves afterward. Cover your skin with protective clothing that can be washed in detergent and hot water after removal.

Proper identification will go a long way to alleviate worry about removal. MSU Extension bulletin E-2935, Giant Hogweed: An attractive but dangerous federal noxious weed, has a good pictorial description with other useful advice. Good quality digital images taken with a camera or cellphone can also be identified by MSU Diagnostic Services if emailed to pestid@msu.edu

Small seedlings can be controlled with a labeled herbicide containing Glyphosate but most references state that a mature giant hogweed plant will not succumb to a single application. Controlling with a herbicide will require tenacious attention, reapplication to basal sprouts and a keen eye for germinating seedlings as seedlings can germinate for several seasons.

Look-a-likes

Giant hogweed has certainly been confused with some of its benign relatives including our native Angelica and cow parsnip. Both of these plants are stately and dramatic looking but not nearly so large as giant hogweed. MSU Extension bulletin E-2935 has excellent comparison photos.

Find out about other educational resources and classes at www.migarden.msu.edu and at Rebecca Finneran’s blog. You can contact the MSU Master Gardener Lawn and Garden Hotline at 1-888-678-3464 with your questions.

This article was published by MSU Extension. For more information, visit http://www.msue.msu.edu.