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: St. Johnswort in bloom
Photo by: D.G. Swan
  
Weeds : St. Johnswort, common (Goatweed, Klamathweed) : Hypericum perforatum
(revision date: 9/3/2015)

Family: Clusiaceae (Guttiferae)
Cycle: Perennial
Plant Type: Broadleaf

Biology
Common St. Johnswort is an erect shrubby plant one to three feet high arising from a taproot. Many stems arise from the base of the plant, each having numerous short, leafy branches. The branches may root where they contact the ground. The oval leaves are opposite and attach directly to the stems. Each leaf has obvious veins and transparent dots which appear as punctures. The showy flowers appear in early summer. Each has five yellow petals with black dots at the margins and a distinctive cluster of many yellow stamens in the center. Seeds have a sticky coating which aids in dispersal. SPECIAL INFORMATION: Common St. Johnswort is toxic to animals. When eaten by white or light-colored animals, a skin irritation in the presence of sunlight can occur. Affected animals may not die due to poisoning, but may refuse to eat resulting in weight loss and eventual death. Skin reactions may also occur in humans. Several insects contribute to biocontrol of this weed. It is commonly mistaken for tansy ragwort. In WASHINGTON, common St. Johnswort is designated as a Class 'C' noxious weed. In OREGON, it is a Class 'B' weed. Management of this species may be required by law in your county. Consult your local Noxious Weed Control Board for more information.
Habitat
St. Johnswort is usually found on dry soils, often in sandy or gravelly areas. It is a common weed on roadsides, grazing lands, waste places, and other areas which are not frequently cultivated. It occurs both east and west of the Cascades.

Management Options

Non-Chemical Management
  • Maintaining a healthy planting or turf area to provide competition will prevent weed establishment.
  • Reduce weed infestation by handpulling weeds.
  • Careful digging is useful to manage weed populations. However, digging can carry undesirable weed seed to the surface and foster further germination.
Select non-chemical management options as your first choice!

Chemical Management

Apply according to label instructions. It is not usually a problem in healthy established turf. Glyphosate products should be applied as spot treatments only! 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
  • dichlobenil
Turf areas
  • products containing 2,4-D
Bare ground areas
  • glyphosate
Images

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Caption: St. Johnswort in bloom
Photo by: D.G. Swan
Caption: St. Johnswort flowers
Photo by: D.G. Swan