Weed of the Month: Common Milkweed

Common Milkweed

Photo: University of Kentucky's College of Agriculture, Food, and Environment

Common name: Common Milkweed
Scientific name: Asclepias syriaca L.

Life Cycle: Perennial
Origin: North America
Poisonous: Yes

Common milkweed, sometimes called milkweed, occurs throughout North America except in the extreme southern, southwestern, and far western states. This deep-rooted perennial broadleaf weed can reach four to five feet in height, and mature plants are woody at the base of the plant. This species is frequently found in pastures, edges of woods, and roadsides. It reproduces from seeds and buds on a deep root.

Twenty to 130 small greenish-white to greenish-purple flowers typically bloom at the common milkweed's terminal (tip of the stem). Leaves and stems contain a white, milky sap. A mature plant produces leaves that are opposite along a stout stem and might also produce several fruits, each containing many seeds. At maturity, the fruit opens and wind disperses the seeds.

Common milkweed produces cardiac-glycosides that are toxic to horses and might cause depression, irregular heartbeat, diarrhea, overall weakness, and labored breathing. Death might occur within 24 hours. Green leaves are the most toxic, but dried leaves in hay are also toxic.

Controlling common milkweed in pastures is very difficult. Property owners might be able to remove small populations effectively by hand weeding and removing the deep taproot. Mowing is generally ineffective, and treatment with herbicides might require multiple applications. Remove mowed or herbicide-treated plants from the field to avoid animals eating the dying or decaying plants. Consult your local Cooperative Extension Service personnel for a list of herbicidal controls in your area.

William W. Witt, PhD, a research in Plant and Soil Sciences, provided this information.

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