Editor’s note: This is part of a series of regular columns by the Minnesota Department of Agriculture on the state’s noxious weeds.
Giant hogweed, Heracleum mantegazzianum, is a stunningly tall plant with a serious public health risk. When the sap comes in contact with skin and is exposed to sunlight, it can cause painful blisters and scarring. Additionally, the sap in contact with eyes can result in blindness.
Originally brought to North America as an ornamental plant, it escaped cultivation and can be found in isolated pockets in many states. Fortunately, it has not been confirmed in the state of Minnesota, although it has been found growing in parts of Wisconsin.
Giant hogweed has many identifiable characteristics. It has deeply cut leaves up to five feet across, and the plant flowers on a 10-15 foot stalk. The plant produces large clusters of tiny white flowers that reach up to two and a half feet across. The stalks are two inches in diameter and hollow with purple mottling. Both the stems and undersides of the leaves are covered in coarse white hairs. It can be mistaken for cow parsnip (Heracleum maximum), a native plant that is common throughout much of Minnesota, has similar leaves and flowers, and reaches 3-10 feet tall with 4-8 inch flowers. However, giant hogweed has much larger, strongly dissected leaves and huge flowers.
The impacts of giant hogweed are numerous. Not only is giant hogweed a serious public health hazard, it can also negatively impact soil dynamics, fisheries, and outcompete native plants. In states where it has been confirmed, it can be found growing in yards, ditches, along stream banks, in disturbed areas, open wooded areas, and thrives in sunny locations. Giant hogweed spreads by seed that can be moved by wind, water, wildlife, and humans.
Management of giant hogweed requires careful handling. Appropriate protective clothing including gloves, goggles and long sleeve shirts should be worn and contact with the stems should be avoided. Management priorities include early detection and seed dispersal prevention. Cutting the flowers to prevent the spread of seed can be an effective management practice, in combination with applying herbicide to the foliage.
Even though this plant has not yet been discovered in Minnesota, the Minnesota Department of Agriculture regulates giant hogweed as a prohibited noxious weed on the eradicate list because of its close proximity of establishment in Wisconsin. It is also a federal noxious weed regulated by the U.S. Department of Agriculture. By law, all above and below ground plant parts must be destroyed, and no transportation, propagation, or sale of the plants is allowed.
If you suspect you have seen giant hogweed, please contact the MDA’s Arrest the Pest voicemail at 888-545-6684 or email@example.com.