Health Protection

                        F a c t s

Giant Hogweed

What is Giant Hogweed?

Giant Hogweed (Heracleum mantegazzianum) is a perennial plant that can grow 4 – 6 metres (15 - 20 feet) tall and has stout, dark reddish-purple stems with spotted leaf stalks.

Where is Giant Hogweed Found?

Giant Hogweed may colonize in a variety of habitats but is commonly found along roadsides, wooded open space areas between residential communities, streams, and rivers. It prefers moist soils and partial shade; however, it may grow in full shade to full sun.

Why is Giant Hogweed Dangerous?

The plant produces a clear watery sap from the leaves and especially the stem. The sap contains furanocoumarin that causes the skin to be photosensitive. After contact with Giant Hogweed, exposure to sunlight may cause severe blistering, burns, and sometimes inflamed linear lesions on the skin. The blisters can develop into purplish or blackened scars. These reactions can occur up to 48 hours after contact and can lead to recurrent dermatitis in some cases. Avoid contact with eyes as temporary or permanent blindness can result.

Control Methods

The preferred method of control is Integrated Pest Management (IPM). The goal of IPM is to maximize effective control and minimize negative environmental, economic and social impacts.

Management Plan

• Single mature plants can be dug up if care is taken to remove at least 1 – 1.5 metres (4 - 6 feet) of the root. Smaller plants may be pulled but root fragments are likely to re-sprout.

• Large established infestations require several control techniques. Control large plants, young plants and seedlings with herbicide or by digging them up. Keep in mind that younger plants are more resilient and may be present in greater numbers. Seedlings can break off when being pulled from more compact soils leaving the root that continues to grow. The majority of seeds fall to the ground within 4 metres (10 – 12 feet) of the parent plant. This area should be treated for potential growth.

• Remember to avoid all contact with plant sap. Wear appropriate personal protective gear for your eyes and skin (for example, gloves and goggles).

• Check with your local landfill site for the best method to dispose of Giant Hogweed.

• Monitor the area for at least 3 years and repeat the control treatment as needed.

• Replace Giant Hogweed with native species or grasses.

• Mechanical removal through mowing will only be effective for short periods of time. Some plants will send up stronger re-sprouts even after being cut back; it is best to dig these up.

• Chemical control may be the most effective treatment option, although it may take several years to eradicate the plants if they are well established. If herbicides are used, ensure their use is permitted to the site and follow all directions on the label.

What to Do if Contact Occurs

Wash affected area immediately, avoid direct exposure to sunlight and seek medical advice.

Source:
King County

Department of Natural Resources and Parks

Water and Land Resources Division

Seattle, WA, USA

http://dnr.metrokc.gov/weeds