- Pest Type: Weed
- Crops Affected: Wheat, Cotton, Potatoes, Soybeans, Corn
- Scientific Name: Asclepias syriaca
- Pest Order: Asclepiadaceae
Common milkweed is a perennial weed with stout, erect stems (0.6-2 m tall). All parts of the plant exude a milky sap when broken.
Reproduction is by seeds and rhizomes. In the spring, plants develop from buds either on the stem base or from rhizomes. Shoots emerge from April through May. Cultivation can fragment and spread roots and rhizomes. Seeds are dispersed by wind in late summer and fall.
Most milkweed plants emerge from overwintering root buds. These are more robust than seedlings and lack cotyledons. Hypocotyls of seedlings are light green and smooth. Cotyledons are dull green, oval, rounded at the tips (1.2 cm long).
Young leaves are opposite, dark green, waxy, oblong, pointed at the apex, with a prominent white midvein on the surface of the leaf. Seedlings do not flower during the first year of growth.
Stems are usually branched, hollow, erect, covered with downy hairs, and exude a milky sap. Stems are green, becoming red later in the season. Leaves are oblong-elliptic to oval, 7-20 cm long, opposite, occasionally whorled, on short petioles (about 8 mm). Leaf blades are green and smooth on the upper surface, with a prominent white midvein, and lighter green and downy hair beneath. Margins are entire; pinnate veins do not reach the leaf margin.
The characteristic pods turn grayish brown and persist on dead stems throughout winter. Pods are shiny yellow on the inside. Some seeds may remain within the pods for an extended period.
Common milkweed is frequently found in meadows and roadsides and is a weed of nursery crops and agricultural crops. It is particularly a problem under no-till and reduced-tillage systems. It prefers well-drained soil and does not tolerate frequent mowing or cultivation.
Common milkweed is found throughout the northeastern United States, south to northern GA, and west to the Rocky Mountains.
Hemp dogbane is closely related. It too is a perennial weed with opposite leaves and milky sap, but its leaves are smaller than those of common milkweed; and its stem is much-branched in the upper half of the plant. Showy milkweed is also similar, but its flowers and hood are larger.