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: Poison hemlock leaves
Photo by: T. W. Miller
  
Weeds : Poison hemlock : Conium maculatum
(revision date: 6/9/2014)

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

Biology
Seedling poison hemlock plants are rosettes of finely divided, fern-like leaves which closely resemble carrot leaves. Mature plants grow six to eight or more feet tall from a large white taproot that is solid throughout. The alternate, fern-like leaves have a distinct, unpleasant odor. The stout, hairless stems are erect and branching, and are marked with purple spots. Small white flowers occur in large, open, umbrella-shaped clusters at the tips of branches. Each flower cluster is supported by its own stalk. The rough, gray-brown seeds are distinctly ribbed. SPECIAL INFORMATION: All parts of this plant are poisonous, particularly the large white taproot and the seeds. This plant can be mistaken for parsley (Petroselinum crispum) or wild carrot (Daucus carota). In WASHINGTON and OREGON, poison hemlock is designated as a Class 'B' noxious weed. Management may be required by law in your county. In addition, it is on the Oregon noxious weed quarantine list, which prohibits sale, purchase, and transport of plants, seeds, and plant parts. Consult your local Noxious Weed Control Board for more information.
Habitat
Poison hemlock commonly grows on the borders of fields, roadsides, and waste areas. It can tolerate poorly drained soils and may also be seen on ditch banks and along streams. It is not usually a problem on maintained lawn and turfgrass.

Management Options

Non-Chemical Management
  • Cultivation (rototilling or hoeing) will effectively eliminate plants.
  • Reduce weed infestation by handpulling weeds.
  • Mowing to prevent seed production is a very effective means of management. In lawns, mowing regularly at the proper height for the grass species may help minimize weed growth and invasion.
  • 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 directions. 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
Turf areas
  • 2,4-D + MCPP + dicamba
Bare ground areas
  • glyphosate
Images

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Caption: Poison hemlock leaves
Photo by: T. W. Miller
Caption: Poison hemlock umbel
Photo by: T. W. Miller
Caption: Poison hemlock fruits
Photo by: T.W. Miller
Caption: Poison hemlock
Photo by: D.D. Tapio
Caption: Poison hemlock flowers
Photo by: T. W. Miller
Caption: Poison hemlock seeds
Photo by: T. W. Miller
Caption: Poison hemlock stem
Photo by: T. W. Miller
Caption: Poison hemlock
Photo by: T. W. Miller
Caption: Poison hemlock seedling
Photo by: T. W. Miller