Weeds: Giant hogweed – Heracleum mantegazzianum

• Family: Apiaceae (Umbelliferae)
• Cycle: Perennial
• Plant type: Broadleaf

Biology

Giant hogweed is a short-lived perennial plant, typically surviving 2 to 5 years. The hollow stems are robust (two- to four-inch diameter), hairy, ribbed, and blotched with purple. The stems have distinct, protruding white hairs that are especially noticeable at the nodes and the base of the leaf stems. The alternate leaves may reach five feet across and are deeply lobed or toothed. Leaf stems also have purple blotches. The flat-topped flower heads are umbrella-shaped and may reach over two feet across; individual flowers are small and white. Plants usually die after they bloom and produce seed. Superficially, giant hogweed resembles the native cow parsnip (Heracleum maximum), but there are two distinct differences. Cow parsnip is typically only 3 to 8 feet high, while giant hogweed grows 10 to 15 feet high. Also, the undersides of cow parsnip leaves have soft, wavy, shiny hairs. Giant hogweed leaves have stiff, dense, very short hairs on the underside. SPECIAL INFORMATION: Avoid skin contact with sap. Skin contact with giant hogweed sap, followed by exposure to sunlight, can result in a photosensitive reaction in some people. Symptoms include painful, burning blisters which can develop into purplish or blackened scars. Eye contact with sap can result in temporary or permanent blindness. In WASHINGTON, giant hogweed is designated as a Class ‘A’ noxious weed. Eradication of the weed is REQUIRED by state law! In OREGON, it is designated as both a Class ‘A’ noxious weed and a target or ‘T’ weed subject to priority prevention and control. Eradication or intensive control may be required in your county. In addition, giant hogweed is on the noxious weed quarantine list for both Washington and Oregon. Sale, purchase, and transport of plants, plant parts, and seeds is prohibited. Consult your local Noxious Weed Control Board for more information.

Habitat

Giant hogweed can be found in damp areas.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

• Careful digging is useful to manage weed populations. However, digging can carry undesirable weed seed to the surface and foster further germination.
• Cut the stems at the base to remove flower and seed heads prior to seed dispersal.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

• Apply according to label instructions.
• Glyphosate products should be applied as spot treatments only!
• Do not touch the weed with bare hands, as it is toxic to skin.
• NOTE: Some ingredients listed here are only available in combination.
• Read the label carefully on combination products to make sure the product is suitable for your specific situation.

Additional Images