White Snakeroot (Ageratina altissima) is a common perennial herb native to North America, often found in wooded areas and thickets. Although considered a native wildflower, it is widely classified as a serious weed in agricultural and garden settings, primarily due to its aggressive spread by both seeds and rhizomes. Its high toxicity intensifies its weed status, posing a significant threat to livestock and indirectly affecting human health.
Identifying White Snakeroot
White Snakeroot is an upright, branched perennial that can grow to a height of one to five feet. It has slender, smooth, or slightly hairy stems emerging from fibrous roots. The plant prefers partial shade and moist, rich soils, making it common in woodlands, along stream banks, and in neglected pastures.
The leaves are arranged oppositely along the stem. Each leaf is broadly ovate, or somewhat heart-shaped, with sharply toothed edges and a rounded base. A long, slender leaf stalk attaches the leaf to the stem, which can help distinguish it from similar-looking plants.
The plant produces its characteristic white flowers late in the growing season, typically from July through October. These small, tuft-like flowers are grouped tightly into flat-topped clusters at the ends of the branches. This late-season bloom makes it a noticeable white presence when many other wildflowers have finished flowering.
The Hidden Danger: Understanding Tremetol Toxicity
The danger of White Snakeroot comes from tremetol, a toxic compound found in all parts of the plant, including the roots and foliage. Tremetol is a fat-soluble alcohol that acts as a metabolic poison affecting the muscles, particularly the heart. This toxicity persists even when the plant is dried, meaning hay contaminated with snakeroot remains a threat.
When grazing animals like cattle, horses, sheep, and goats consume the plant, they develop a condition known as “trembles,” characterized by listlessness, weight loss, and pronounced muscle tremors. The animal’s breath may also carry a distinct ketone odor. The poison can be fatal to livestock, often leading to death within days of symptom onset.
The compound tremetol is unique because it is readily excreted and concentrated in the milk of lactating animals. Humans who consume this contaminated milk or dairy products develop a severe illness historically known as “Milk Sickness.” This indirect poisoning resulted in thousands of deaths among 19th-century settlers, most notably Abraham Lincoln’s mother.
Symptoms of Milk Sickness in humans include severe vomiting, abdominal pain, constipation, and intense muscle tremors. While rare today due to modern farming practices that mix milk from large herds, the risk remains when consuming raw milk from animals grazing freely in wooded areas.
Eradication and Management Strategies
Controlling White Snakeroot is necessary for property owners with pets or livestock. For small, isolated patches, manual removal is an option, but safety precautions must be followed. Wear gloves to avoid contact with the plant’s toxins and ensure the entire root system is removed to prevent regrowth from the rhizomes.
Pulled material should be disposed of in the trash, not composted, to prevent further spread. Regular mowing before the late-summer flowering period can also weaken the plant by preventing seed production and depleting root energy reserves.
For larger infestations, chemical control using herbicides is often the most effective method. Products containing the active ingredients glyphosate or triclopyr have good activity against the plant. Triclopyr is often preferred in grassy areas because it is a broadleaf-specific herbicide that will not harm the surrounding turf.
When applying any chemical treatment, it is necessary to follow the product label directions precisely and to use spot applications to avoid harming desirable nearby plants. Extra caution must be exercised during removal or treatment, especially in areas accessible to children and grazing animals.