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Giant hogweed plant appears across county

It’s big, it’s beautiful and it is very, very toxic.

In fact, giant hogweed is a Class A noxious weed, and contact with any part of the plant can result in serious burns, similar to chemical burns or fire burns, said Jeff Lesh, WeedWise Program technician with the Clackamas County Soil and Water Conservation District.

If the sap comes into contact with eyes, it can cause temporary or permanent blindness, he added.

Lesh described giant hogweed as a “limited problem” in the county, saying the conservation district is dealing with a “handful” of patches at the moment.

But because he and his colleagues want to stay on top of the problem before it becomes more widespread, he is asking that people who think they have a giant hogweed plant on their property notify him at once.

There are two main ways to recognize the perennial plant, Lesh said, including the fact that it produces dinner-plate size white, umbrella-shaped flowers, similar to, but much larger than Queen Anne’s lace.

But the really definitive means of identification is the size of the plant, which grows above 10 feet, and produces massive leaves, which can be 3 to 5 feet in width.

It can easily be confused with cow parsnip or even poison hemlock, but “no other plant that has a similar flower grows above 10 feet,” Lesh added.

Weeds spreading

Giant hogweed is native to Eurasia and was intentionally planted in the United States in the early 20th century as a “horticultural curiosity” in ornamental gardens. It spreads by seed, and can crop up anywhere, including residential areas.

“It will spread naturally along roadsides, in ditches and by creeks and streams. It is mostly spread by human assistance in contaminated soil or intentional planting,” Lesh said.

In Clackamas County, giant hogweed has been found on residential properties. The city of Portland is managing an outbreak of the plant near Mississippi Avenue.

Probably the most publicized appearance of the noxious plant was in June 2012, when it was found at Hartley Elementary School in Gresham, a school located at Northeast 185th and Glisan. This was a doubly dangerous location, because there is a public park directly behind the school.

“The parents of some of the neighbor kids said some of their children had recurring burns and rashes,” due to contact with the giant hogweed, said Sam Leininger, the WeedWise Program manager for the conservation district.

He added that the boys had cut off the hollow stems of the plants and used them as “telescopes,” endangering their eyes.

Eradication important

People who think they have a patch of giant hogweed on their property should contact the conservation district at once, Lesh said.

“Call us and don’t disturb the plant. If property owners want to control the plant themselves, that is an option, or we’ll take care of it for free,” he said.

by: PHOTO BY SAM LEININGER, CCSWCD - The leaves of the giant hogweed, pictured left, can grow from 3 to 5 feet in width. The plant is a noxious weed, and the sap is the most dangerous part.He added that if property owners try to remove the plant themselves, they may inadvertently spread the problem, by moving contaminated soil.

“Our job is to identify the plant, prevent the spread of it, control the plant and eradicate the plant infestation,” Lesh said.

Above all, he added, people need to be aware that giant hogweed is regulated by state and government laws, and is not allowed to be intentionally cultivated or transported, unless it is being taken for disposal.

The Oregon Department of Agriculture “wants to know where the plants are, and they want them to be controlled because there are human-health concerns,” Lesh said, noting it is illegal to buy giant hogweed or any Class A noxious weed at a nursery.

The soil and water conservation district specializes in early detection and rapid response programs emphasizing education and cost-effective prevention to help property owners eradicate weeds of any kind and to stay on the lookout for weeds before they become widely established on their property.

Lesh added that free brochures are available to help property owners identify the “Terrible 10” noxious weeds, including giant hogweed.

Get weed wise

To learn more about the WeedWise Program or to report a weed infestation, call the Clackamas County Soil and Water Conservation District at 503-210-600 or email This email address is being protected from spambots. You need JavaScript enabled to view it..

To pick up brochures, stop by the CCSWCD office at 221 Molalla Ave., Oregon City, Suite 102.




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