Harmful Invasive Species: Heracleum mantegazzianum, or Giant Hogweed
The invasive giant hogweed, a striking plant with a dangerous side, has been making its presence known in Pennsylvania and New York, as well as other regions. Its establishment has been challenging to track due to the lack of detection of its rosette stage.
This biennial plant, which prefers full sun and moist, well-drained soil, can be identified by its large compound umbel of white flowers, large, deeply incised leaves, and prominent white hairs and purple blotches on its stems. It flowers in late June to early July, and its inflorescence forms a flat top with a diameter up to 2.5 feet.
While the giant hogweed may seem like an attractive addition to any garden, it poses a significant threat. Its greatest danger lies in the effect its sap has on humans, causing severe burns, blistering, and potential for permanent scarring and blindness.
Control methods for giant hogweed include digging, mowing, cutting, removal of umbels, grazing, and herbicide application. Applications of triclopyr and glyphosate in the fall (after the first frost) to plants established that season usually provide the most effective control in a single application. Triclopyr and glyphosate are effective herbicides for controlling giant hogweed, with glyphosate requiring a minimum of 0.75 pounds of acid equivalent per acre.
However, managing giant hogweed is not a one-time task. Continuous management for five years is required to attempt to eradicate it. Furthermore, multiple applications per year for consecutive years may be necessary to completely control a giant hogweed population.
It's important to note that giant hogweed can be easily confused with other species, including angelica, poison hemlock, wild carrot, cow parsnip, common pokeweed, giant ragweed, and ironweed. Protective clothing and eyewear should be worn when working around giant hogweed, especially when cutting, to avoid splashing the toxic sap onto the skin.
The giant hogweed was first observed in Ohio in the early 20th century and is believed to have been introduced from Europe as a culinary herb and subsequently spread as an invasive species. It has been found in rich, moist soils along roadside ditches, stream banks, vacant farmland, and fence and tree lines.
The giant garlic mustard (Alliaria petiolata) is another invasive species that shares similar habitats with the giant hogweed. It was first observed in Ohio in the early 20th century and is believed to have been introduced from Europe as a culinary herb and subsequently spread as an invasive species.
In conclusion, while the giant hogweed may be beautiful, its dangerous sap makes it a hazard to human health. Proper identification and continuous management are crucial in controlling its spread and ensuring the safety of both humans and native flora.
