Poison hemlock

Conium maculatum

Poison hemlock

Roots: White taproot, poison.

Stems/Leaves: During the first year the plant grows the leaves can reach a size of up to 11 feet across.  The stems on the poison hemlock are rounded, scabrous, and purple spotted.  The stems also appear to be ribbed because of there veins.  By the time it gets more growth the leaves are up to 18" long and 12" across.  The leaves become smaller further up the stems.  The leaves are a little bit like a fern and the surface has a filmy look.  (1)

Flowers: The flowers are located at the top part of the stem and are small and white.  These groups of flowers are about 2-5 inches across.  Each umber has about 12-25 flowers in it.  Each individual flower has 5 petals on it.  The flower also consists of 5 spreading white stamens and a white nectar pad in the center.  The flower spans about 1/8 of an inch when it is fully open.  (1)

Fruits and Seeds:  The seeds are usually a grayish brown in color and the length is approximately 2.0 mm.

Reproduction:   The seeds fall off the plant around were it is inhabiting.  The seeds then grow into a bigger colony. (1)

Life Style/Habits/Life Duration:  The weed likes to to have full sun to a light shade.  They also like to be in a moist place with fertile loamy soil.  The growth usually occurs during the spring and after dropping it's seeds they turn yellow and die in the summer.  (1)

Environments Favorable to Infestation: The habitats for the poison hemlock are usually around the areas of the edges of degraded wetlands and prairies.  They also appear in low-lying areas along small rivers, banks of drainage ditches, thickets, woodland borders, fence rows, springs, low-lying areas along railroads and roads.  Also, they show up in pastures and abandoned fields.

Methods of Control: The best time to get rid of the poison hemlock is when they start to come in the spring.  Now you can pull them out but not with your bare hands as they are poisonous.  Using washable gloves will work just fine if you want to pull them out.  You can also mow them down during the spring.  (1)

Biological Control:  The European palearctic moth, or hemlock moth (Agonopterix alstroemeriana (Clerck)) can help.  The only known host plant for the moth is the poison hemlock.  The larvae eats the poison hemlock foliage, buds, immature seeds, stem tissues and flowers.  They usually eat these in the spring and early summer. When many of them are on one plant it may be defoliated.  The larvae are also thought to prevent seed production. Adult moths emerge in summer and consume some foliage but the larvae are the most effective life stage. (3)

Herbicides: You can use broad leaf herbicides.  The herbicide 2,4-D applied to the early stages of growth will kill it. (1,2)

Warning: This plant is quite poisonous, especially the roots.

Literature Sited:
  1) http://www.illinoiswildflowers.info/weeds/plants/poison_hemlock.htm
  2) http://www.vet.purdue.edu/depts/addl/toxic/plant28.htm
  3) http://museum.gov.ns.ca/poison/hemlock.htm
  4) http://gardening.wsu.edu/column/05-23-99.htm
  5) http://www.oneplan.org/Crop/noxWeeds/nxWeed21.htm
  6) http://www.ansci.cornell.edu/plants/conium.html
  7) http://cal.vet.upenn.edu/poison/plants/pppoiso.htm
  8) http://www.botanical.com/botanical/mgmh/h/hemwat19.html
  9) http://www.all-creatures.org/picb/wfshl-waterhemlock.html
10) http://plants.usda.gov/java/profile?symbol=COMA2

1)  Hilty, John.  Poison Hemlock.  January 26, 2006.  March 16, 2006. <http://www.illinoiswildflowers.info/weeds/plants/poison_hemlock.htm>

2) Robson, Mary.  Poison Hemlock - Dangerous to People and Animals.  May 23, 1999.  Washington State University.  March 16, 2006. <http://gardening.wsu.edu/column/05-23-99.htm>

3) Pokorny, Monica L. and Roger L. Sheley.  Poison Hemlock.  Oct. 2000.  Montana State University.  March 16, 2006. <http://www.montana.edu/wwwpb/pubs/mt200013.html>

Page by: Dimitri McLughlin, 3/14/06. 

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