Poisonous Weeds in Midwest Pastures & Hay

Poisonous Weeds in Midwest Pastures & Hay

People that raise livestock have an increasing awareness that poisonous plants can affect their animals. Part of this is due to the ever increasing population of horse owners and the growth in management intensive grazing systems. But do not forget that you do not only have to watch your pasture ground closely, but your hayfield or purchased hay as well.

Poisonous plant questions are also more frequent in dry years as droughts create situations in which animals often graze plants they would otherwise not eat and producers may harvest fields or plants that are not usually harvested to have adequate feed stock for the winter.  Additionally, weeds not usually considered toxic might become poisonous under certain condition. For example, weeds may become more palatable to livestock following an herbicide application in a pasture or fencerow. This may result in animals eating plants they would normally avoid consuming. All areas of the country have different species of concern and your local extension agent or university may be of assistance.

What are the Plants That Cause Animal Poisoning?
The book “Poisonous Plans of the Midwest” (Evers and Link 1972) includes 70 species. Also, Indiana lists 53 plants as potentially poisonous to animals on their “Indiana Plants Poisonous to Livestock and Pets” web site… http://vet.vet.purdue.edu/toxic/cover1.htm

Laatly,  I highly recommend the Purdue University Guide to Toxic Plants in Forages… https://www.extension.purdue.edu/extmedia/ws/ws_37_toxicplants08.pdf

Many universities offer outstanding websites and documents, usually complete with photos and the information you require.

Below is partial list of plants common in the Midwest that are capable of affecting animal health and the toxin they contain.

The list below is in the following format:

White Snakeroot

White Snakeroot


Bracken Fern
woods and open areas; all part poisonous

pastures, esp. wet areas; causes sharp drop in milk production; toxin lost on drying forage

Prussic acid
common in fencerows and woods

cultivated fields, pastures; esp. sandy soils; seedlings and seeds toxic

Hemp Dogbane
Apocynin & other glycosides
all plant parts have milky sap; fields and roadsides

Hoary Alyssum
horses are particularly sensitive

wet or dry areas of pastures and roadsides; all parts toxic

seldom eaten because of spines

Alkaloids and others
all plant parts toxic

Nitrate and Oxalate
common field weed; high in feed value

Solanine and other glycoalkaloids
all parts poisonous under certain condition; ripe berries almost nontoxic

acorns and young leaves and shoots are of concern

oxalate and Nitrate
common field weed; many species; prostrate and tumble pigweed common in pastures

Poison hemlock
roadsides, edges of fields and waste areas where soil is moist; all parts highly toxic
These excerpts were taken from an article by Jerry Doll, University of Wisconsin, Poisonous Weeds of Pastures & Forages.  Remember your local extension service can help you with identification, control, and challenges you may face.  Be safe, know what is growing in your pasture and hay fields.  Be safe and drop by for more on weeds throughout different regions of the United States.

J.R. Brown
Written by J.R. Brown

Retired USAF SNCO, Hay & Cattle Farmer, GIS User, Antique Farm Machinery Collector, Favorite old iron...anything Oliver, Moline, Farmall, or Allis-Chalmers.

4 Comment responses

  1. Avatar
    July 22, 2017

    Good article on poisonous weeds. Everyone should check their fields. I recently discovered poison hemlock growing around creeks and wet areas of my farm. I have been spaying and digging up these plants for the past 3 years and I think I finally got them under control. We lost a cow a few years ago and our vet did not know why it died. Now I believe it could have ate some poison hemlock.


  2. Avatar
    June 15, 2015

    Great article, good to read some hay articles for smaller hay folks like myself.


  3. Avatar
    February 25, 2015

    Hi, just wanted to mention, I enjoyed this post. Keep on posting!


  4. Avatar
    June 30, 2014

    I raise horses and came across your Poison Weeds in Pasture and Hay. Thanks for writing about this for the midwest area. Also, thanks for the reference links in the article. I know little about what to look for in hay and your blog article was helpful. Can you write more about what to look for in hay and provide more links. Thanks.