Species specifics: Hemp dogbane

Photo Credit : Larry Allain, hosted by the USDA-NRCS PLANTS Database.

Fast facts

Easily confused with milkweed species by the untrained eye
A native perennial commonly in hayfields across much of North America
Highly toxic and can be lethal to cattle

What to look for

Hemp dogbane (Apocynum cannabinum) is a native, stemmy perennial plant that can be easily confused with milkweed species to the untrained eye and is highly toxic to cattle.

The weed averages 3 to 4 feet tall and can reach up to 6 feet. While it produces a milky sap substance like milkweeds, one of the easiest ways to distinguish hemp dogbane is by its long, narrow reddish-brown, solid stems that branch in the top canopy. Leaves are almost hairless, opposite and are 2 to 5 inches long, with shapes ranging from long and narrow to more egg-shaped, with a prominent white midvein.

Another notable difference from milkweeds is hemp dogbane’s flower type and seed shape. After blooming small white flowers at the end of stems and branches from July to August, hemp dogbane produces narrow, brown sickle-shaped pods that hang below the stem and can be 4 to 8 inches long. Because this plant spreads by both seeds and horizontal roots, they are often found in colonies due to spread by rhizomes and regrowth after mowing or cutting, such as in hayfields.

Hemp dogbane contains toxic cardiac glycosides that affect the heart, and ingestion of only 15 to 30 grams to be lethal to cattle. The toxicity risk is present in both fresh and dried hemp dogbane. In pastures, cattle will often avoid the weed unless no other forage is available, such as in overgrazing conditions. However, the most common risk of poisoning comes from stored forages and hay cut from hemp dogbane-infested fields, where it’s more difficult for animals to sort out the weeds. The invasive weed is also toxic to horses and dogs.

Where it is found

Found in crop fields, pastures and roadsides – think anywhere that has been cut, mowed or tilled – it is a common weed across the United States.

How to treat it

Hemp dogbane is best managed in late spring to early summer when plants are actively growing. Before treating, allow time for plant recovery after cutting.

Tank mix 16 to 20 fluid ounces per acre of DuraCor® herbicide plus 16 fluid ounces per acre of PastureGard® HL herbicide.

For non-residual weed control, apply 1.5 pints per acre of PastureGard HL herbicide alone for successful control of hemp dogbane.

Always read and follow label directions. Under normal field conditions DuraCor® is non-volatile. DuraCor has no grazing or haying restrictions for any class of livestock, including lactating dairy cows, horses (including lactating mares) and meat animals prior to slaughter. Label precautions apply to forage treated with DuraCor to manure and urine from animals that have consumed treated forage. DuraCor is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. PastureGard® HL herbicide is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state.