- Pest Type: Weed
- Crops Affected: Wheat, Cotton, Potatoes, Soybeans, Corn
- Scientific Name: Apocynum cannabinum
- Pest Order: Apocynaceae
Hemp dogbane is a perennial weed with erect stems, branching in the upper one-half; and branching is opposite. Mature plants grow to 0.3-1 m tall. Stems contain a white milky juice.
Reproduction is by both rhizomes and seeds. Seeds are narrowly spindle-shaped (4-6 mm long), reddish-brown, with a tuft of silky hair which is white to tan (1-4 cm long).
Most hemp dogbane plants emerge from overwintering buds on the rhizomes. These shoots lack cotyledons and are more robust than seedlings.
Leaves are opposite, blades are simple, lanceolate to ovate or oblong (2-15cm long and 1.5 cm wide), with a leaf tip (apiculate). Leaf margins are entire, often covered with wax, smooth above, may be sparsely hairy beneath, and pale beneath.
Leaf blades are on short petioles on the primary axis, nearly sessile on branches. Stems branch on the upper half of the plant and branching is opposite. Stems are reddish-brown, smooth, and hairless or nearly so.
Flowers are greenish-white, 5 petals (2-5 mm long and 1.5-2.5 mm wide) are united. The fruit is a follicle (5-20 cm long), straight or curved, sickle shaped, and contains up to 200 seeds.
The seed pods remain attached to dead stems well into the winter.
Common in cultivated fields, especially those with reduced tillage, nursery crops, pastures, rangeland, fence rows, roadsides, and waste areas. It is difficult to control, but does not tolerate frequent mowing or cultivation.
Hemp dogbane can be found throughout the United States (except for souther parts of Florida and Texas) and southern Canada.
Common milkweed is very similar, but has larger leaves and the upper stem is not branched. In addition, the milkweed flowers are larger.