Usually when a plant takes over a pasture, hayfield or crop field, oftentimes the plant is an introduced species, a non-native, but that’s not always the case.
This summer it has been hard to travel anywhere about the county without someone asking me about a plant invading their field. That plant: Hemp Dogbane.
First, kudos to most of the people that have asked me about it, because most of them have already identified the plant as Hemp Dogbane, and not Common Milkweed, which it resembles.
Hemp Dogbane, also known as American Hemp or Indian Hemp, is a native plant and a member of the Dogbane family. Despite having the word “hemp” in its name, Hemp Dogbane is not related to the marijuana plant, rather it is named for its tough, fibrous stems and roots that were occasionally used like hemp fibers for making ropes, baskets and clothing.
Its scientific name, Apocynum cannabinum means “poisonous to dogs” and refers to its similarity to cannabis as a fiber plant. It is found in every county of Ohio, and throughout most of the United States, and can be found nearly everywhere except in the deepest, darkest of woods. This year it has shown a preference for hayfields.
Most people have three questions: What is it? Is it toxic? How do I get rid of it?
As I mentioned earlier, Hemp Dogbane plants (particularly the young plants) look very similar to Common Milkweed, but as they get older the Hemp Dogbane displays a reddish-colored stem, and unlike Common Milkweed, which has a single stalk, the Hemp Dogbane begins to branch out. The leaves on the Hemp Dogbane are narrower than Common Milkweed leaves, however both produce a milky sap – which no doubt contributes to the Hemp Dogbane/Common Milkweed confusion.
From a practical standpoint, Monarch butterflies and their caterpillars avoid and will not eat Hemp Dogbane leaves; people have mistakenly starved captive Monarch caterpillars by mistakenly gathering Hemp Dogbane leaves for them to eat. They just won’t eat them.
Whether Hemp Dogbane is toxic is still a subject of discussion. An online pamphlet from Ohio State University’s College of Food, Agricultural, and Environmental Sciences says this:
“There are no reported cases or direct experimental evidence of poisoning in humans, but hemp dogbane is considered by many to be poisonous to livestock. Several compounds possibly toxic to humans and other animals have been isolated but little is known about if or how they contribute to the toxic nature of the plant. There are reports of horses, cattle, and sheep poisoned from eating green or dried hemp dogbane. At one time, it was considered that 0.5 to 1 ounces of green or dry leaves could kill a horse or a cow. However, recent evidence suggests that this report was the result of an error (emphasis mine).”
In any event, if any local producers have had animals poisoned or sickened by Hemp Dogbane, I haven’t heard of it. Livestock are usually pretty good about eating around the things that taste bad, but a haybale consisting primarily of Hemp Dogbane can’t be a good thing.
Control. Unfortunately, most experts agree on one thing: Hemp Dogbane is difficult to control, and once it takes hold it can be difficult to get rid of it. The most aggressive way of controlling Hemp Dogbane is by fall applications of 2, 4D or other broadleaf herbicides. Alfalfa and winter wheat are good competitors with Hemp Dogbane, and some people have reported success with repeated mowing or soil disturbance (i.e. plowing).
Who knows why this particular plant has been so conspicuous this year? Perhaps the conditions were just right for it. Who knows what next year will bring?
Jim Freeman is employed with the Meigs Soil and Water Conservationist and is a long-time contributor. He can be reached weekdays at 740-992-4282 or at firstname.lastname@example.org