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Agronomic Crops Network

Ohio State University Extension


Milkweed and Hemp Dogbane - Who’s Who?

Common milkweed plant on the left and hemp dogbane plant on the right

This article originally appeared in the Ohio BEEF Cattle Letter

Both milkweed and hemp dogbane have become more apparent in the area over the past week. These two plants are related but have some distinct differences that can help landowners identify them and implement control measures when needed.

Similarities between the two include having creeping roots; leaves that appear on opposite sides of the stem; and they produce a milky sap. Differences include that young milkweed leaves have fine hairs and hemp dogbane are nearly hairless; milkweed stems are generally thick and green, but hemp dogbane stems are usually red to purple and thinner in comparison; hemp dogbane frequently branches in the top canopy, while milkweed will typically not branch unless mowed; and seed pod shape is distinctly different after flowering with milkweed producing an upright tear drop shaped pod and hemp dogbane producing a long bean-like pod that hangs from the plant.

While the usefulness of milkweed in the landscape is often justified for monarch butterfly populations, hemp dogbane has fewer redeeming qualities. Historically hemp dogbane has been used by Native Americans to make rope, clothing, and baskets. Both have the capability of spreading rapidly by their creeping roots and seed production. Both are best controlled in agricultural settings by a combination of strategic mowing and systemic herbicide application.

Both milkweed and hemp dogbane are considered poisonous to livestock. Toxicities can occur from fresh or dried leaves, stems, and roots. While death from poisoning is rare, reduced production efficiency is common if consumed. Symptoms range from mild to severe and include vomiting, diarrhea, coordination loss, tremors, heart problems, respiratory distress, and death.

While eliminating milkweed and hemp dogbane from all ecosystems would be unwise, treatment of some kind is advised in situations where livestock are consuming forage from areas with high populations.

According to the 2021 Ohio, Indiana, and Illinois Weed Control Guide, both milkweed and hemp dogbane are significant agronomic weeds in no-till systems. Various postemergence herbicides can be effective on milkweed and hemp dogbane if the plants are less than eight inches tall. For the best control of the creeping root system, applications of translocated herbicides should be applied when the plants are in the bud to flower stage. Attaining complete control after one herbicide application is unlikely. The most appropriate time to treat and product to use depends on the situation. Commonly used herbicides for suppression or control include glyphosate, 2,4-D, dicamba, and triclopyr products. Always follow the directions printed on the herbicide label for application rates, methods, and concerns.

Learn more about milkweed and hemp dogbane by comparing the photos provided in today’s column or by watching this video from last summer comparing the two plants side by side:

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.