WSU Extension

Hortsense

Weeds
 
Annual bluegrass 
Barnyardgrass 
Bentgrass, creeping 
Bermudagrass 
Bittercress (Shotweed, Hairy bittercress) 
Bittersweet nightshade (European bittersweet) 
Black medic 
Blackberry (Himalayan, Evergreen, Pacific) 
Blue mustard (Purple mustard, Tenella mustard) 
Brackenfern, western 
Buffalobur 
Bull thistle 
Buttercup, creeping 
Canada thistle 
Catchweed bedstraw (Cleavers) 
Catsear, common (False dandelion) 
Chickweed, common and mouseear 
Clover 
Comfrey 
Crabgrass 
Dandelion 
Dock (Curly, Broadleaf) 
Dodder 
Downy brome (Cheatgrass, Downy chess) 
Dwarf mistletoes 
English daisy (Lawn daisy) 
English ivy 
Field bindweed (Wild morningglory) 
Field pennycress (Fanweed) 
Flixweed 
Foxtail (Green, Yellow, Bristly) 
Garden loosestrife 
Giant hogweed 
Goldenrods 
Groundsel, common 
Hawkweeds 
Hedge bindweed 
Henbit 
Herb Robert (Robert geranium, stinky Bob) 
Horsetails (Scouringrush) 
Horseweed (Marestail) 
Knapweeds 
Knotweeds (Bohemian, Giant, Japanese, Himalayan) 
Kochia 
Lambsquarters, common 
Liverworts 
Mallow, common (Cheeseweed, Buttonweed) 
Nightshades 
Oxalis (Creeping woodsorrel) 
Parrotfeather and Eurasian watermilfoil 
Pineappleweed 
Plantain (Broadleaf, Buckhorn) 
Poison hemlock 
Poison ivy and Poison oak 
Prickly lettuce (China lettuce) 
Prostrate knotweed 
Puncturevine (Tackweed, Goathead) 
Purple deadnettle (Red deadnettle) 
Purple loosestrife (Purple lythrum) 
Purslane, common 
Quackgrass 
Red sorrel (Sheep sorrel) 
Redroot pigweed (Rough pigweed) 
Redstem filaree (Stork's bill, Crane's bill) 
Reed canarygrass 
Russian thistle (Tumbleweed) 
Ryegrass, annual (Italian ryegrass) 
Salsify (Goatsbeard) 
Scotch broom 
Shepherd's-purse 
Smartweeds 
Sowthistle, annual and perennial 
Speedwells 
Spurges (Prostrate spurges) 
St. Johnswort, common (Goatweed, Klamathweed) 
Stinging nettle 
Tansy ragwort 
Tumblemustard (Jim Hill mustard) 
Velvetgrass (Common velvetgrass) 
Velvetleaf 
Water primrose 
Waterhemlock, western 
Yellow nutsedge 



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Caption: Giant hogweed patch
Photo by: Washington Noxious Weed Control Board
  
Weeds : Giant hogweed : Heracleum mantegazzianum
(revision date: 6/9/2014)

Family: Apiaceae (Umbelliferae)
Cycle: Perennial
Plant Type: Broadleaf

Use Integrated Pest Management (IPM) for successful weed management.

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

Non-Chemical Management
  • 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.
Select non-chemical management options as your first choice!

Chemical Management

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.

Landscape areas
  • glyphosate
Turf areas
    Bare ground areas
    • glyphosate
    Images

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    Caption: Giant hogweed patch
    Photo by: Washington Noxious Weed Control Board
    Caption: Giant hogweed flowers
    Photo by: Washington Noxious Weed Control Board
    Caption: Giant hogweed hollow stems
    Photo by: Washington Noxious Weed Control Board