Poison Hemlock   (Conium maculatum) 

DESCRIPTION

Poison hemlock is a biennial herb, 6 to 8 feet tall, that has a stout taproot. It is an erect plant, with hollow multi-branched stems, which are ridged and covered in all stages of growth with purplish spots and blotches. The leaves are alternate very small and finely divided in fern-like lacy pattern, the lower leaves are on long stalks which clasp the stem and the upper leaves are on shorter stalks. Flowers are small white in color and are formed on many branched umbrella-shaped clusters. It flowers from May to August. The seeds are concave and ribbed, in pairs and about 1/8th of and inch long. The plants leaves has a strong, distinct parsnip odor. The seeds contain the highest concentration of poison. The conium alkaloids are volatile and can even cause toxic reactions when inhaled. Photo credit: Dr. Mary Ann Rose, The Ohio State University How to distinguish from other plants Water hemlock does not have the same main taproot and stem. Instead, water hemlock has a branching, tuberous root stalk similar to that of a dahlia plant. The lower part of the stem of water hemlock is divided into chambers which contain its toxicant. Poison Hemlock is also commonly confused with wild carrot, cow parsnip, etc. Human deaths have occurred from harvesting and consuming the roots as wild carrots or parsnips. The stems should always be checked for red mottling. However, this characteristic is not always readily apparent. Photo Credit:  School of Veterinary Medicine, Purdue University

(Source: 1.Poisonous Plants Informational Database, Cornell University, http://www.ansci.cornell.edu/plants/index.html; 2. Integrated Weed Management on the Prineville District, Bureau of Land Management (BLM), http://www.or.blm.gov/Prineville/weed/hemlock.htm)

IMPACTS

Poison Hemlock is a very poisonous plant, that thrives in poorly drained riparian areas. All parts of the plant are poisonous, humans are usually poisoned when mistaking the plant for wild parsley. The toxic components include the volatile alkaloids coniine and gamma-conicine. A lethal dose for a horse is 4 to 5 pounds of leaves, cattle may be poisoned with 1 to 2 pounds, and sheep with a half pound or less . Humans are often poisoned, mistaking the roots for parsnips, the leaves for parsley, or the seeds for anise.

Affected animals show signs within 2 hours of eating the plant, and tend to become nervous, and will tremble and become uncoordinated. After the excitement phase, the animal becomes depressed. The heart and respiratory rates slow down, the legs, ears and other extremities become cold, colic and/or bloating may occur. Even at this stage, the animal may not die, but may remain like this for several hours to days, and then recover. In lethal cases, the animals tend to die within 5 to 10 hours after the onset of the clinical signs, typically from respiratory failure (in which case the mucus membranes will appear blue). A mousy odor has been reported to emanate from affected animals.

The primary time of year for poison hemlock is spring, often when there is insufficient forage available. At this time, the plant may also be more palatable. The toxicity increases throughout the growing season, and the roots become toxic only later in the year. Once dried, the toxicity is considered to be reduced but not eliminated.

Poison hemlock can also cause birth defects in ruminants and swine, with cattle and swine more susceptible than sheep and goats. The most often reported birth defects are cleft palate and spinal abnormalities. The gestational ages that have been associated with birth defects are: for goats, days 30 through 60; for cattle, days 40 through 70; for pigs, days 30 through 60. The birth defects resemble those seen with lupine, with lupine being the more dangerous plant.

FIRST AID: If animals are seen ingesting poison hemlock, call a veterinarian immediately. Treatment consists of eliminating the toxin from the gastrointestinal tract and providing supportive care. If the animals become comatose but do not die, they will require intense nursing care until they recover.

SAFETY IN PREPARED FEEDS: Reportedly, poison hemlock has a decreased toxicity when dry, but hay that contains a large proportion of poison hemlock may still cause problems (besides, it would have a low nutritional value). Recommendations are to feed little or no hay that contains poison hemlock. Seeds may contaminate grain-type feeds, making these feeds unsafe for consumption.

PREVENTION of LIVESTOCK POISONING: Swine paddocks should be monitored for poison hemlock because swine will readily eat it. Poison hemlock is not highly palatable to cattle, horses, and sheep and rarely will they eat a toxic amount of it if more palatable vegetation is available on the range. Because conium alkaloids are teratogenic to cattle, care should be taken that cows in the first 3 mo of pregnancy not be grazed on sparse pastures with an appreciable population of poison hemlock. The seeds contain the highest concentration of toxicants. Therefore, feed grain can potentially be contaminated with poison hemlock. Although, herbicides and routine cultivation severely reduce the amount of poison hemlock in grain fields, seed contamination is still a potential danger in unsprayed or newly established grain fields.

(Source: 1. Poisonous Plants Informational Database, Cornell University, http://www.ansci.cornell.edu/plants/toxicagents/piperidi.html; 2. School of Veterinary Medicine, Purdue University,  www.vet.purdue.edu/depts/addl/toxic/plant28.htm; 3. Integrated Weed Management on the Prineville District, Bureau of Land Management (BLM), http://www.or.blm.gov/Prineville/weed/hemlock.htm)

(Source: 1.Poisonous Plants Informational Database, Cornell University, http://www.ansci.cornell.edu/plants/index.html)

(source from: 1. Integrated Weed Management on the Prineville District, Bureau of Land Management (BLM),  http://www.or.blm.gov/Prineville/weed/hemlock.htm)

Poison Hemlock: Poisonous Plants Informational Database, Cornell University  
    http://www.ansci.cornell.edu/plants/comlist.html
This site provides a brief description about distribution, description, how to distinguish from other plants, and toxic ingredient (Piperidine Alkaloids). 

Poison Hemlock: School of Veterinary Medicine, Purdue University
    http://www.vet.purdue.edu/depts/addl/toxic/plant28.htm
This site explains a toxicity of Poison Hemlock and general descriptions. 

Butte-Silver Bow Weed Control Information Page: Butte-Silver Bow Local Government, MT
    http://co.silverbow.mt.us/weeds/poison%20hemlock.htm
This page contains a description of poison hemlock and pictures.

Poison Hemlock: USDA, Washington DC
   http://newcrop.hort.purdue.edu/newcrop/herbhunters/poisonhemlock.html
This page includes a description of poison hemlock and figures.

Integrated Weed Management on the Prineville District, Bureau of Land Management (BLM)
    http://www.or.blm.gov/Prineville/weed/hemlock.htm
This site describes a general description, impacts, and control. 

Colorado Weed Management Association
    http://www.cwma.org/poison_hemlock.html
This contains a brief description of Poison hemlock.

Identifying Noxious Weeds of Ohio: Poison Hemlock (Bulletin 866-98), The Ohio State University

Link   http://ohioline.osu.edu/b866/b866_6.html
Describes Habitat, Life cycle, First Year Growth Habit, Second-Year Growth Habit, Leaves, Stems, Inflorescence, Root, Similar plants, and problem with three figures.