White Snakeroot: The Silent Cattle Killer
By the Wilson family, in memory of Beauford Wilson, invasive weed expert
Beauford would walk our properties with us and have us identify weeds. As many parents do, he was passing down the industry knowledge he had acquired over half a century to us, his children and grandchildren. One weed in particular this time of year he would give us a history lesson on it's devastation: white snakeroot.
Beauford passed before he could put all of it on paper. This post shares what we remember of his lessons on white snakeroot, why it still costs cattle producers today, and how to keep it out of your herd. Fall is when this weed does its damage, so there is no better time to read it.
The short answer: is white snakeroot poisonous to cattle?
Yes. White snakeroot (Ageratina altissima, formerly Eupatorium rugosum) is one of the most dangerous pasture weeds in the eastern United States. It contains tremetol, a fat-soluble toxin that causes "trembles" in cattle and passes into milk, where it once caused "milk sickness" in people.
Who it hurts: cattle, horses, sheep and goats; nursing calves are especially at risk because the toxin concentrates in their mother's milk.
When: late summer through fall, when the plant blooms and other forage runs short. Toxin levels peak in August and September.
Where: shady woods edges, creek banks, wooded pastures and fence lines.
Hay is not safe: the plant stays toxic after it is dried and baled.
Outcome: affected cattle often die within 2 to 10 days of showing signs. There is no antidote.
Prevention: fence cattle out of wooded areas in fall, keep pastures well fed, and pull, mow or spray the plant before it seeds.
How do you identify white snakeroot?
Beauford often pointed out that people who lose cattle to snakeroot have usually walked right past it. It doesn't look dangerous. It looks like something you'd put in a vase. Here's what to look for:
Feature | What you'll see |
Height | 1 to 4 feet, upright and branching |
Leaves | Opposite each other on the stem, egg- to heart-shaped, coarsely toothed edges, pointed tips, on long leaf stalks |
Flowers | Small, fuzzy, bright-white clusters at the tops of the branches, flat-topped |
Bloom time | Mid-summer into fall, often until first frost |
Habitat | Shade and part shade: woods edges, fence rows under trees, creek and river banks, wooded lots and old clearings |
Life cycle | Perennial; comes back from the same roots every year and spreads by seed |
Look-alikes to rule out: boneset (leaves wrap around the stem with no stalk), wild ageratum or mistflower (blue-purple flowers) and white asters (daisy-like flowers with a yellow center). When in doubt, take a sample to your county extension office.
A good rule of thumb: if you have shade, cattle and September, go look for it.
How does white snakeroot poison cattle?
The poison is tremetol, a fat-soluble mix of compounds whose most toxic part is called tremetone. Because it dissolves in fat, it builds up in the body over days of grazing, and it is carried out in the milk of a lactating cow.
That last part is what makes snakeroot so cruel. A lactating cow may show few signs herself because she is shedding the toxin in her milk. Her nursing calf drinks it, and the calf gets sick or dies. In beef herds, it's often the calves you lose first.
Cattle don't usually seek it out. Most cases come in late summer and fall, when pasture grass is short from drought or overgrazing and the green snakeroot under the trees is the only thing left to eat. Some cattle will eat it voluntarily, so a full pasture alone doesn't make you safe.
Signs of trembles in cattle
Depression, listlessness and loss of appetite
Stiff, unsteady walking; standing with legs spread apart
Muscle tremors, especially in the legs and muzzle, that get worse when the animal is moved or worked
Constipation and a sweet, acetone-like smell on the breath (ketosis)
Lying down and unable to rise, then coma
Death, often within 2 to 10 days of the first signs
In horses, the same plant damages the heart and can cause permanent heart failure. Sheep and goats are poisoned by smaller amounts than cattle.
What to do if you suspect it
Move the whole herd off the pasture right away and pull all hay from that field.
Separate nursing calves from cows suspected of eating it, and feed the calves another milk source.
Call your veterinarian. There is no antidote, and your veterinarian can advise on supportive care. Don't force sick cattle to walk; exertion makes trembles worse.
If an animal dies, ask your vet about a necropsy. Snakeroot leaves can be identified in the rumen, which confirms the cause.
Milk sickness: how white snakeroot killed Abraham Lincoln's mother
White snakeroot isn't just a cattle problem. It changed American history.
In the early 1800s, settlers pushing into Indiana, Illinois, Ohio, Kentucky and Tennessee turned their milk cows loose in the woods to graze. The cows ate snakeroot, and families who drank the milk, or ate the butter and beef, came down with a mysterious illness: weakness, vomiting, tremors, a foul breath and, often, death. They called it "milk sickness" or "the slows." It wiped out whole families and emptied entire settlements.
As Beauford wrote in the email above, milk sickness claimed thousands of lives in the early 1800s, and one of them was Nancy Hanks Lincoln, Abraham Lincoln's mother. She died of it in October 1818 at Little Pigeon Creek, Indiana, when Abe was nine years old. Some of her neighbors died of it the same season.
For decades no one knew the cause. Frontier doctor Anna Pierce Hobbs Bixby of southern Illinois is credited with linking the illness to white snakeroot in the 1830s, but the medical world didn't fully accept the connection until researchers isolated tremetol in the 1920s.
Today, milk sickness in people is extremely rare. Commercial milk is pooled from many farms, which dilutes any toxin from a single cow. Families who drink raw milk from their own cow on wooded pasture are still at risk.
Still on the list of plants that will kill you
White snakeroot's reputation hasn't faded. Christine Vrey of Our World included it in her article "Top 10 Plants That Will Kill You."
What white snakeroot costs the cattle industry
Snakeroot losses rarely make the news because they happen a few head at a time, on one farm, in one fall. But they add up, and every one of them is preventable. Here is where the money goes:
Dead calves. Nursing calves take the heaviest hit. Every lost calf is lost income for the operation.
Sick cows and lost weight. Animals that survive trembles go off feed, lose condition and may not breed back on time.
Lost milk. On dairies or family-cow operations, milk from exposed cows can't safely be used.
Spoiled hay. Hay cut from a field with snakeroot in it carries the toxin into winter, when you're least expecting trouble. A contaminated cutting may have to be thrown out.
Vet bills and labor. Diagnosis, supportive care and moving cattle off a pasture all cost time and money.
Hard-to-diagnose losses. There is no routine lab test for tremetol, so many deaths are never pinned on snakeroot, and the weed keeps doing its work year after year.
Often, the real cost is the herd that gets hit two or three falls in a row before anybody walks the tree line and finds the cause.
How to protect your herd from white snakeroot
The good news: snakeroot is one of the easier poisonous plants to beat, because it lives in predictable places. These are the basics Beauford taught us, in line with common extension recommendations.
Scout in late summer. Walk every wooded edge, creek bank and shaded fence row from August on, when the white blooms make it easy to spot. Mark the patches on a map or your phone.
Fence out the woods in fall. If you can't clear it, keep cattle out of wooded areas from late summer until a hard frost has killed the top growth. Temporary electric fence works fine.
Don't make them hungry. Most poisonings happen when grass runs short. Keep stocking rates in line with your forage, and start feeding hay before pastures are grazed into the ground, especially in a dry fall.
Pull small patches. For a few plants, pull them out by the roots (wear gloves), bag them and remove them from the pasture. Never leave pulled plants where cattle can reach them.
Mow before seed. Mowing before the plants set seed in fall cuts down next year's crop. Remove the clippings or keep cattle off until they've broken down.
Spray when it's growing. Broadleaf herbicides work best on young, actively growing plants in spring and early summer. Your county extension office can recommend a product labeled for pasture use in your state. Always follow the label's grazing and haying restrictions, and keep cattle off until sprayed plants are completely dead and gone, because wilting can make poisonous plants more appealing to livestock.
Check your hay. Don't cut hay from fields or field edges with snakeroot in them. Inspect bales you buy, especially from wooded or bottomland fields.
Follow up every year. Snakeroot is a perennial and seeds blow in from the woods. One season of work won't finish it; consistent scouting will.
Frequently asked questions about white snakeroot
Is dried white snakeroot in hay still poisonous to cattle? Yes. The plant is most toxic when green, but it stays toxic after it is dried and baled. Hay with snakeroot in it can poison cattle in winter.
What time of year is white snakeroot most dangerous? Late summer and fall. Toxin levels are highest in August and September, the plant is in bloom, and pasture grass is often short.
Can people get sick from white snakeroot? Yes, by drinking milk or eating dairy products from a cow that ate it. This is "milk sickness," which killed thousands of settlers in the early 1800s, including Nancy Hanks Lincoln. It is very rare today because commercial milk is pooled from many farms, but raw milk from a single family cow is still a risk.
Why do calves die when the cow seems fine? Tremetol is fat-soluble and passes into milk. The cow sheds much of the toxin in her milk, so she may show few signs while her nursing calf is poisoned.
How much white snakeroot does it take to kill a cow? The toxin builds up over days of grazing, and the plant's strength varies from one patch and season to the next, so there is no safe amount. Assume any grazing on it is dangerous.
Is there a treatment for trembles? There is no antidote. Remove animals from the source right away, rest them, keep nursing calves off exposed cows and call your veterinarian for supportive care.
Does white snakeroot grow in my area? It is native across most of the eastern half of the United States and southeastern Canada, from the Atlantic west to the Great Plains, wherever there are woods and shade.
Walk your fields
Beauford spent fifty years teaching people to look down at their pastures instead of past them. He believed most weed problems are lost or won on foot, one fence row at a time, and white snakeroot proves him right: it hides in the same shady places every year, and it waits for a hungry fall.
So this week, while the white blooms are still showing, walk your tree lines. Bring your kids or grandkids along and teach them what this plant looks like. That's how Beauford passed it down to us, and it's how we'd like to pass it on to you.
If this helped, share it with a neighbor who runs cattle near the woods. It might save a calf, or a whole herd.
Disclaimer: This article is for general educational purposes only and is not veterinary, medical or legal advice. If you suspect poisoning in livestock or people, contact your veterinarian or physician right away. Before using any herbicide, consult your county extension office and follow the product label. The farm assumes no liability for actions taken based on this article.
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