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Homestead dairy herds can encounter a wide variety of poisonous plants, but few have the potential to be as troublesome or frightening as white snakeroot (Ageratina altissima, formerly Eupatorium rugosum). This medium-sized perennial herb, which we first learned about in 2008, can be toxic not only to the livestock consuming it, but to humans consuming dairy products and meat from those livestock.
One of the first things you’ll tend to learn upon Googling this plant is that it killed Abraham Lincoln’s mother, along with many other settlers, during America’s westward expansion. Surprisingly, for such a concerning plant, it’s a relatively obscure member of the “watch out for this” club; many books we’ve read about small-herd livestock don’t even mention it.
In this post, we’ll discuss where to look for white snakeroot, how to identify it, the control methods we’ve attempted, and what recent research is available about its toxicity to goats, humans and other livestock.
How to Find and Identify White Snakeroot
White snakeroot can be found across the eastern half of North America. In our central Missouri landscape, snakeroot seems to like shady areas, especially near or under cedar trees, though it can also be found in hardwood forests. It doesn’t like full sun or too much competition from grass. It’s a perennial, growing from the same root stock year after year, and often grows in dense clusters where it’s almost the dominant plant by the time it flowers in late summer.
Early in the season (May, for us) it can be hard to notice — just a small, obscure herb poking up among plants. By midsummer in Missouri, its tall, tough stem supports opposite leaves with toothed edges; flowering begins in August and peaks in September.
Why is White Snakeroot a Threat?
White snakeroot contains a cocktail of toxic compounds that can poison goats and other livestock, causing neurological disorders commonly referred to as “trembles”, which can be fatal. This toxicity can be passed through the milk, causing similar problems in humans or nursing young. Unfortunately, the toxicity also seems to be sporadic and unpredictable, making management decisions and diagnosis challenging. During the 1800s, when it was common practice to graze livestock in forested or newly cleared areas, so-called “milk fever” was a common cause of death for European-American settlers, though the link to white snakeroot wasn’t proved until decades later.
Such poisoning seems to have subsided as newly cleared land stabilized into established open pasture, and livestock were increasingly kept out of woodlands. Thus snakeroot poisoning all but vanished as an issue for generations, and knowledge of its dangers diminished. Modern agricultural and botanical resources tend to assume that livestock don’t interact with woodlands anymore, considering snakeroot poisoning a quaint quirk of history.
However, with the recent resurgence in homestead farming and mixed land use, livestock such as goats once again have a higher chance of encountering white snakeroot with serious implications for the herd and its humans. We learned about snakeroot by accident, when Joanna connected a common plant in our landscape with a passage in the book Missouri Wildflowers, typical of the carefree treatment of historic (rather than modern) snakeroot toxicity:
“This plant is the cause of ‘milk-sickness’; it is poisonous to cattle and killed many early settlers who drank poisoned milk, including Abraham Lincoln’s mother.”
Learning More about White Snakeroot
Any online search will lead you to websites listing similar basic information about the plant, including the unfortunate Nancy Lincoln. However, we’ve been frustrated by a lack of specific information about just how toxic the plant is, what level of consumption should be a concern, and so on. It’s one thing to know a plant is theoretically toxic, it’s another to know whether you should panic about that one mouthful your goat just ate.
If you wish to dig deeper, searching the USDA’s Agricultural Research Service website produces many useful results. In addition, the ARS publishes online summaries of scientific research, in language accessible to laypeople. This is particularly useful for research published in scientific journals that are otherwise locked behind paywalls. To browse these summaries and other information, just enter “white snakeroot” or any other topic into the site’s search bar. Even a quick read through the results yields useful detail and context that many basic websites don’t convey. For example:
A 2010 study in the Journal of Food Chemistry concluded (in the ARS summary) that: "Different types of white snakeroot that have different chemical compounds may explain the sporadic and unpredictable toxicity of white snakeroot to livestock and humans.”
A 2015 study in the Journal of Agricultural and Food Chemistry states (in the ARS summary) that: "Although a toxic extract from the plant was shown to cause the disease in the late 1920s, it was also later demonstrated that the extract was a mixture of many different compounds. . . . Goats dosed with the white snakeroot plant material were poisoned demonstrating for the first time that white snakeroot is a potent myotoxin in goats. However goats dosed with the hexane extract did not poison suggesting that another compound besides tremetone may have a significant role in the toxicity of the plant”
There is much that modern science still doesn’t understand about the specific toxic threat to livestock and humans from this plant, but interested readers can learn a lot from perusing these summaries. We’re not qualified to issue specific conclusions about snakeroot, but have been concerned enough to undertake control measures in our grazing areas.
Controlling White Snakeroot
So now you’re worried, and wondering what to do. Unfortunately, there’s no easy solution. Snakeroot is susceptible to herbicides, but this is an unacceptable option on our farm. In any case, we can’t envision a way to kill snakeroot without killing swaths of desirable plants around every little cluster of stems, and ruining the pasture for grazing. We’ve had some success with changing its habitat by opening up brushy areas to full sun, an on-going project anyway as we attempt to restore a more open savannah landscape on our overgrown farm. The best (if obnoxious) approach in our experience is to hand-weed our grazing areas.
Snakeroot has shallow roots (see photo 4), and under the right conditions it’s pretty easy to pull. Don’t just break off the stems, as it’s a perennial that will grow right back from the rootstock. Get a good grip at the base of the plant, and if the ground isn’t too dry, the whole cluster will pull right up like a charm. Early in the season, it’s harder to see and identify but a lot less bulky. By mid/late-summer, it’s easy to see as it begins to tower over other plants, and the white flowers begin to stand out. We work through a given area before the goats move onto it, using a consistent search pattern to cover the area.
One important warning: snakeroot is a prolific producer of seed, and once the seed starts forming on the plant, it will continue to do so and become viable even after the plant is pulled. Our harvested bundles of snakeroot are piled in areas we don’t intend to graze; often we’ll hot compost the bundles, though some sources suggest burning them. We’ve been doing this for many years, and had hoped to see a significant reduction in plant population by now. Yet the stuff keeps showing up again, which we attribute to a large latent seed bank built up in the soil over many years of non-management. Still, it’s the best approach we’ve tried, or seen suggested online.
How Worried Should You be about White Snakeroot?
We don’t know. To judge from the historical record, brush-fed goats and their owners should be dropping like flies throughout snakeroot’s range, but that doesn’t seem to be happening (or it’s going undiagnosed). Research has shown that snakeroot’s toxicity is unpredictable; is there something different between modern snakeroot and the 1800s plant?
We’ve kept dairy goats on a snakeroot-infested landscape since 2008, but have also put a lot of time into pre-weeding our grazing areas, as our goats live full-time on pasture from spring through fall. Our goats have eaten mouthfuls at times, from individual plants or clusters we missed, with no observable effects on their kids or ourselves, the primary consumers. One Texas-based researcher we contacted years ago told us that a goat needed to eat several pounds of snakeroot to be of concern, but we don’t have further proof of that claim.
Studies have clearly documented the potential toxicity in a lab setting, but not in the context of a modern homestead dairy herd. We hope this article raises awareness of the potential problem, so that individuals can make more educated decisions about landscape and dairy animal management.
All photos by Joanna Reuter
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