White Snakeroot

clusters of small flowers are in full bloom on a green lush snakeroot plant.

Photo by Ansel Oommen, Bugwood.org.

Up until the early 1900s, “milk sickness” caused by white snakeroot (Ageratina altissimo; Eupatorium rugosum) poisoning was a relatively common, ever-present danger for settlers and farmers who pastured cattle on woodlands and waste ground and drank milk or ate meat from their own cows. That potential danger still remains for families who drink milk from their own cows. However, commercial milk is safe because any milk from a suspect cow is diluted, being mixed with milk from countless “white snakeroot-free” cows before sale to consumers. Of possible concern may be the novice, “back-to-the-landers,” who buy a wooded acreage, build a home and pasture a cow or two for their own milk.

A group of cattle browse on grass on a hilltop near an edge of a woodland in autumn. To the right of the cattle is an old barn.
Photo by Carolyn Wilman, Pixabay.com

Usually, a cow had to eat a substantial amount of foliage before enough poisonous tremetol—a mixture of toxic ketones—accumulated in its body to sicken and kill it. However, enough tremetol could accumulate in the milk to kill a human or a nursing calf before it sickened the cow. Thus, a person could sicken and die from milk sickness after drinking milk from apparently healthy cows. Many midwestern county histories recorded incidents of death from “the slows” as the sickness was often called. During early times, a few Indiana county records attributed nearly half of all deaths due to milk sickness; the most well-known case being that of Nancy Hanks Lincoln during 1818 in Spencer County. She was Abraham Lincoln’s mother.

White snakeroot grows in woodlands, thickets, and waste ground. Disturbances of fire and grazing may increase its occurrence. Controlled burns of woodlands that had a history of livestock pasturing years before may bring on a renewed flush of white snakeroot. Heavy, continuous pasturing for prolonged periods of time increases disturbance and may contribute to increased white snakeroot presence. Although it is less palatable than most woodland plants, livestock may eat more of it because their plant choices become limited in degraded and disturbed woods, particularly during fall and during drought conditions.

Clusters of tiny white flowers are in full bloom on a green plant with heart shape leaves with a toothed edge.
Photo by Ansel Oommen, Bugwood.org.

If white snakeroot is present in a woodland, do not pasture cattle, sheep, goats, or horses on it. Horses are particularly sensitive to tremetol. Pasturing concerns are less early in the growing season but increase later as forage becomes limited and livestock are more likely to eat the less palatable white snakeroot.

This 1- to 3-foot-tall native perennial grows throughout most of Illinois. When it blooms, white snakeroot is most easily recognized and thus easier to assess its overall occurrence in a woodland. Often, blooms are first noted along woodland lanes because this plant prefers partial sunlight to light shade. In Illinois, the flat topped to slightly rounded clusters of small white flowers appear from late July through mid-October. Flowers have five petals, and flowerheads have a fuzzy look. The leaves are paired opposite to one another along the main stem and are somewhat heart shaped. Leaves vary from 3 to 5 inches in length and have a toothed edge. Once you become familiar with the growth habits, habitat, and appearance of white snakeroot, it is easy to identify.


Robert J. Reber is an emeritus faculty member in the Department of Food Science and Human Nutrition of the University of Illinois at Urbana–Champaign. He has been a lifelong student of many aspects of the Natural World, including archaeology. Bob has served as a managing editor and author for publications such as The Illinois Steward magazine and the Illinois Master Naturalist Curriculum Guide.


Robert J. Reber is an emeritus faculty member in the Department of Food Science and Human Nutrition of the University of Illinois at Urbana–Champaign. He has been a lifelong student of many aspects of the Natural World, including archaeology. Bob has served as a managing editor and author for publications such as The Illinois Steward magazine and the Illinois Master Naturalist Curriculum Guide.

Share this Article

Submit a question for the author



Explore Our Family of Websites

Similar Reads


Oak leaves curled up and deformed do to herbicide drift on an oak tree limb.

Dainty white flowers with five petals and little yellow centers are blossoming amongst new leaves on a bush in springtime.

Serviceberry: A native plant for all seasons


A brown, tan and black chipmunk picks up an acorn resting on a gravel surface.

A Society of Acorn Relocators


A group of people stand together and pose for a photo on a green lawn. In the background is a green leafy tree. In the foreground is a concrete sidewalk.

Restoring Volo Bog


A close up of red seeds on a bush with bright red leaves during the autumn season. In the background blue sky peeks through between the leaves. Overlaying the photo is a logo with a red "X" with the text "Invasive Species Series."

Burning Bush Threatens Migrating Birds


In a mowed grassy area, a wild turkey is showing off to potential females in full mating display with its tan fanned out. In the background are a couple of wild turkeys.

NWTF, Our Fiftieth and Beyond


A prescribed burn is being conducted on area with trees scattered throughout. Light filters through the trees and is absorbed by smoke wafting up from the ground. In the background is a bright blue sky.

Tracking Wild Turkey Hens in Illinois


A spring ladies tresses orchid grows near a blue lake. The flower has small white flowers arranged in a spiral around the stem. It grows in a patch of tall grasses near the lake with trees visible in the distance behind the lake.

A bloomed leadplant, full of violet blossoms, stands among the prairie grass at Illinois Beach State Park.