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Photo Credit: Portland BES -
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Giant hogweed seedlings. Beware giant hogweed seedlings look very similar to native cow parsnip seedlings!
Also known as: giant cow parsnip, giant cow parsley, cartwheel flower
Caution
Giant hogweed is a serious health hazard to humans and other animals. Its white, watery sap is a phototoxic – meaning if it comes into contact with your skin or eyes and then is exposed to sunlight, it can cause blistering, painful burns or even blindness.
Description:
| Life Cycle: | Perennial (life cycle lasts more than one year) |
| Early Detection and Rapid Response species: | Yes |
| Height: | 10 to 15 feet (3 to 4.5 meters) |
| Stem & Leaf Description: | Stems are hairy and can vary from entirely purple to mostly green with raised, purple-red blotches. Leaves can be up to 5 feet (1.5 meters) wide, with three deeply cut leaflets per leaf. |
| Fruit & Flower Description: | The flowers grow in flat-topped clusters that look like umbrellas. Each flowering head is made up of hundreds of tiny white flowers. It spreads by seed and each plant can produce up to 100,000 seeds. |
| Bloom Time: | May to July |
Habitat:
- It can be found in forests, riparian areasRiparian Areas Areas of land that occur along the edges of rivers, streams, lakes, and other bodies of water., and wetlands.
- Prefers moist soils and shaded environments.
Impact:
- Poses a health hazard to humans. Its white, watery sap makes skin sensitive to ultraviolet light, resulting in severe burns and blisters when exposed to the sun.
- It also spreads quickly and can crowd out crops and native plants.
- It can also impede access to riverbanks due to its size and toxicity.
What we’re doing about it:
- Giant hogweed is a priority species for the Tualatin SWCD. As such, our Invasive Species Program has been actively monitoring and treating it throughout the watershed.
- If identified within Washington County, a specially trained crew can come out survey for giant hogweed. If found, the crew will treat the infestation for free.
What you can do about it:
- If you think you’ve spotted giant hogweed, please report it to the Oregon Invasives Species Hotline.
- Do not treat this weed yourself!
Look-alikes:
Giant hogweed looks extremely similar to native cow parsnip (Heracleum maximum). Cow parsnip’s sap can have similar effects, though it is usually less potent than hogweed.
When mature, cow parsnip is smaller than hogweed and grows to 7 feet tall. Before maturity, the distinguishing features are much more subtle: cow parsnip’s stems do not have purple-red blotches and its leaves are not as deeply cut.
Noxious Weed Listing:
| State of Oregon: | Class A, T |
| State of Washington: | Class A |
More Resources:
Download the Giant Hogweed Best Management Practices Factsheet
- Pacific Northwest Weed Management Handbook: Giant hogweed
- University of California, Weed Research & Information Center: Giant hogweed