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AUBURN UNIVERSITY — Farmers and outdoorsmen beware. Poison hemlock is now creeping across Alabama. This non-native plant may appear aesthetically pleasing in a landscape to some, but this species has unique toxic traits. Nancy Loewenstein, an Alabama Cooperative Extension System forestry, wildlife and natural resources specialist, said people should learn to recognize and avoid this plant, also keeping pets and livestock away from it.

Identification

Conium maculatum, commonly known as poison hemlock, is a herbaceous plant that was introduced to the United States more than 200 years ago. It is a biennial species, meaning it lives for two years.

"In the first year, plants form a rosette or cluster of leaves spreading outward from a short stem and not gaining much height," Loewenstein said. "In the second year, with the help of a well-established taproot, the plants bolt, reaching heights of 3 to 10 feet tall and producing many flower heads. After seeds have set, the plants die but remain standing, and seeds are dispersed to begin the process over again."

This plant blooms in the early summer with clusters of small, white, five-petaled flowers that are arranged in the shape of an umbrella. The leaves of poison hemlock are pinnately compound, meaning that each leaf contains many leaflets. The leaflets are smooth, not hairy and are finely divided and taper to a point. The outline of the entire leaf forms a broad triangle or oval shape. One of the most obvious identifiers of this species is the purple splotches on its stem.

Safety and control

Poison hemlock contains strong, alkaline oils that are highly toxic. Every part of the plant — from the roots to the flowers — is poisonous, especially if ingested. The oils trigger a reaction in the body and can cause dermatitis (skin irritation). Like poison ivy, the more contact with the plant, the worse the reaction of the skin. If ingested by people or pets, reactions can include muscle paralysis, suffocation and, eventually, death.

"Do not eat any part of this plant," said Kerry Steedley, an Alabama Extension forestry, wildlife and natural resources regional agent. "Livestock typically avoid eating these plants, as the leaves are unpalatable, but if other feed is not available, the plants may be ingested."

Steedley said the best control methods for poison hemlock are cultivation and herbicide application. Using tillage prevents seedlings from reentering the soil and mitigates the spread of the plant. If choosing to physical removal the plants by hand, be sure to wear gloves, long sleeves, long pants and protective eyewear. Because poison hemlock remains toxic after removal, all plant material must be bagged and placed in the trash.

Glyphosate, a nonselective herbicide ingredient, offers effective control if applied in spring. The spray target for herbicides are first-year rosettes, however second-year stems prior to the flowering stage are appropriate as well. Poison hemlock seeds require monitoring for germination several years following plant removal, as they remain viable. Repeat treatment steps until eradication of this undesired species is complete.

Learn more

Poison hemlock remains a species of concern in Alabama, along with many others including cogongrass, Chinese tallowtree, kudzu and more. To learn more about these species and how to control them, visit the Alabama Extension website, www.aces.edu.