It is prudent to be aware of poisonous plants. They may exist on roadsides, rights-of-way, or other secluded areas, then find their way to livestock pastures and home landscapes. This article will just scratch the surface of poisonous or toxic plants, but I’ll provide links to more extensive sources of information.
Some of the toxic weeds to look for in Indiana include cress-leaf groundsel, white snakeroot, Carolina horsenettle, climbing or black nightshade, horsetail, jimsonweed, common milkweed, hemp dogbane, common pokeweed, common burdock, cocklebur, stinging nettle, star of Bethlehem, buttercup, and poison hemlock.
There are many potential toxic weeds in pastures. Fortunately, many of them don’t taste very good and livestock generally avoid them until they have no other choice. Additionally, the level of toxicity and symptoms they produce will vary among plant species and from one livestock or animal species to another. I’d encourage producers to walk their pastures periodically to search for toxic plants that may have invaded the area.
“Controlling weeds in pastures is an important thing to consider so you have pasture resources that are appropriate for the livestock being fed, particularly for those weeds that don’t have any nutritional value or are toxic,” said Keith Johnson, Purdue Extension forage specialist.
When it comes to home landscapes, be aware of poison hemlock, castorbean, yew, and wild black cherry, among others. Some plants may have been purposely planted, while others may be bordering or encroaching upon the home landscape.
Poison hemlock has become more common in recent years. It is a biennial weed that exists as a low-growing herb in the first year, then bolts to three to eight feet tall in the second year to produce white umbrella-like flowers. It is often not noticed until the bolting and reproductive stages of the second year. With its fern-like foliage, poison hemlock is often confused with wild carrot, but poison hemlock can be distinguished by its purple blotches and lack of hairs on the stems. The sap in this plant is toxic, so wear gloves if you are hand-pulling poison hemlock. Besides livestock potentially affected in pastures, dogs could also be affected.
Castorbean is a large showy plant, used in landscapes for its large foliage and overall size. It has reddish to purple stems with 5- to 9-pointed finger-like lobes on umbrella-like leaves, which grow up to 30 inches across. While it can be a showy landscape feature, be aware that all parts of the plant are poisonous to people, pets, and other animals. The seeds and leaves are particularly poisonous, and death is possible. If poisoning is suspected, people should seek immediate medical help, and pets should be taken immediately to a veterinarian.
Yews are a common shrub planted around homes. I recently wrote about the dangers of throwing yew clippings into a pasture, as livestock could die if they consume too many clippings. Yews can also affect dogs.
Wild black cherry is a native tree that could be in areas bordering landscapes. Wilted or bruised leaves, twigs, and branches convert harmless compounds to poisons that could be harmful. This is common after summer storms or damage from ice. Livestock, dogs, and cats could be affected, and death is possible. Related trees within the Prunus genus may also contain these potentially toxic compounds, although fresh fruit is unaffected.
For more information, see “Indiana Plants Poisonous to Livestock and Pets,” at https://ag.purdue.edu/btny/purdueweedscience/wp-content/uploads/2021/01/WS-9.pdf. See “Guide to Toxic Plants in Forages,” at https://www.extension.purdue.edu/extmedia/WS/WS_37_ToxicPlants08.pdf. See further information on toxic pasture weeds at https://ag.purdue.edu/department/arge/PACs/sipac/toxic-plants/index.html. Finally, a former Purdue consumer horticulture specialist authored a comprehensive article on poisonous plants in the home, yard, and garden at https://www.purdue.edu/hla/sites/yardandgarden/some-plants-are-poisonous/.