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Zero Tolerance

02:10AM Aug 27, 2014

Don’t let giant hogweed escape control this fall 

When you think of your worst weeds on the farm, pigweed, marestail and waterhemp probably come to mind. Giant hogweed, on the other hand, most likely isn’t on your radar—but it should be. While hogweed competes with plants for nutrients, worse yet, it poses a risk to human health.
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Giant hogweed, a noxious weed found in roughly 16 states, was most likely introduced to the U.S. as an ornamental plant. 

The watery sap from hogweed leaves and stems, in combination with exposure to sunlight, can cause severe blistering burns on skin. The reaction is commonly referred to as phytophotodermatitis, explains Peter Carrington, assistant curator and edible and toxic plant specialist at the W. J. Beal Botanical Garden at Michigan State University. The burns from giant hogweed often require medical treatment and can create extensive, long-lasting scars. If sap from the plant gets in your eyes, it can cause momentary or even permanent blindness.

Pretty, but lethal. To date, giant hogweed has been found in up to 16 states, particularly in the extreme northwest, northeast and upper Midwest states, including Illinois, Indiana, Michigan and Wisconsin. But before you run out to your fields to look for this weed, you need to know its preferred habitat is in disturbed soil along roadsides, stream banks, grass waterways and, surprisingly, home gardens.

There’s a logical reason why giant hogweed, which is on the Federal Noxious Weed List, could be lurking in your backyard: It’s pretty. While it’s a native to the Caucasus Mountains in Eurasia, between the Black Sea and the Caspian Sea, it was introduced in the early 1900s to the U.S. most likely as an ornamental plant. The second potential cause of its introduction here is that its seeds are used in some ethnic food dishes.

"Most giant hogweed, and we find very little in Illinois, occurs around homes and gardens, often where it was planted as an ornamental by individuals not entirely familiar with the species," notes Aaron Hager, University of Illinois Extension weed scientist. 

Identify and treat. The weed’s scientific name, Heracleum mantegazzianum, comes from the Greek hero Hercules. As its name implies, giant hogweed can grow to a large size, up to 15' tall. It has hollow, ridged stems that grow up to 4" in diameter and have dark reddish-purple blotches. Hogweed leaves grow up to 5' wide, and its white flower heads can grow up to 2.5' in diameter. Some people say the weed looks like Queen Anne’s lace on steroids.It’s easiest to identify the weed when it is in the flowering stage, notes Kelly Estes, state survey coordinator for the Illinois Cooperative Agricultural Pest Survey, based in Champaign, Ill.

"Numerous small white flowers are born in June or July in large flat-topped umbels up to 2.5' across," Estes explains. "After the flowers produce their seeds by late-summer, the plant dies back to the thick taproot. Its stem might persist throughout the winter."  

Estes adds that due to its size and rapid growth, giant hogweed outcompetes many native plants. 

Removal protocol. If you locate giant hogweed on your property, use extreme caution in handling it. Make sure you wear gloves, protective clothing and eye protection. If you get sap on your skin, immediately wash the affected area with soap and water, and keep the exposed skin out of sunlight for 48 hours.

Herbicides containing either glyphosate or triclophyr as the active ingredient are effective on giant hogweed, as long as it’s actively growing. Expect to treat the plants for more than one year to eliminate them. If there are flower heads present when you treat, remove them to minimize their opportunity to add to the soil seed bank.

In addition, if you locate giant hogweed on your property, consider calling your state department of agriculture to report the finding before you implement any control measures. Some states have active programs in place to control it and will help you with removal.