Poison Hemlock (Conium maculatum) is an aggressive invader that is found in wet to mesic habitats in the lowland zone and is locally common in southwest BC, particularly in the Vancouver and Victoria areas.
Family: Apiaceae (Parsley).
Other Common Names: Hemlock
Growth Form / Reproduction: Biennial forb.
Agricultural: Poison hemlock crowds out desirable forage species and can poison livestock and humans. Sheep are less sensitive to it than cattle and horses.
Ecological: Although not an aggressive invader, poison hemlock may gradually increase in riparian and lowland communities.
Human: All parts of the plant are highly poisonous and poison hemlock should be handled with care.
Habitat: Poison hemlock is generally found on dry to moist soils, can tolerate poorly drained soils, and tends to be scattered in riparian areas. It is usually found along streams, irrigation ditches, and the borders of pastures and cropland, and it can gradually invade perennial crops.
Status and Distribution: In BC it is found in wet to mesic habitats in the lowland zone and is locally common in the southwest of the province, particularly in the
Vancouver and Victoria areas. It is present in the Kootenay, Okanagan, Mainland, Vancouver Island, and Cariboo regions.
Management Strategy: Biocontrol: Agonopterix alstroemeriana (moth), accidentally introduced into the US, apparently feeds exclusively on poison hemlock. It is found in Colorado and is a biological control agent in Idaho, Oregon, and Washington, where it is effective (William et al. 1996). This species has not been found in BC.
Mechanical: Poison hemlock can be controlled by digging, repeated mowing, pulling, or spring/winter burns. Care should be taken to avoid contact with bare skin (wear gloves). Wash hands thoroughly after handling any part of this plant.
Fire: No information available.
Herbicides: Picloram, dicamba, 2,4-D, and glyphosate have been used for chemical control of poison hemlock. Apply foliar herbicides during the rosette stage with a wick to minimize damage to adjacent desirable vegetation. Cut any stems that arise after treatment. Herbicide treatment may need to be repeated for several years until the seed bank is depleted (Panter and Keeler 1988). Consult the most recent edition of BC Ministry of Agriculture, Food and Fisheries Crop Production Guides for specific recommendations.
Government of British Columbia. 2002. A Guide to Weeds in British Columbia. Crown Publications.