Toxic Parts:
ketones, tremetol
Flower Color:
  • flower color
woodlands, meadows, waterside

Time of Greatest Risk


Geographical Distribution

White snakeroot distribution - United States

Related Species

White Snakeroot

Eupatorium rugosum

Fall Poison, Joe Pye Weed, Richweed, Deerweed, Deerwort,
8/ 10
White snakeroot (Ageratina altissima also known as Eupatorium rugosum) is an erect, branched, perennial herb. White snakeroot blooms during the late summer months, where numerous small heads of white flowers appear at the top of the stem and the ends of the branches. The fruits are distinguishable as brown or black cigar-shaped capsules, single-seeded and tipped with a tuft of white hairs. The leaves are 3 to 5 inches long and petioled, are sharply toothed on the margins, dull on top and shiny on the bottom.

White Snakeroot Toxic Components

White snakeroot contains the ketone tremetol. Poisoning in livestock is sporadic due to the considerable variation in the quantity of the toxin present in the plant---as it varies from location to location and also differs depending on current stage of growth. Tremetol causes hypoglycemia and ketoacidosis by impairing the tricarboxylic acid (TCA) cycle in horses. It causes degeneration of the skeletal and cardiac muscles and injures the liver and kidney. The major effects are related to congestive heart failure. Horses develop a condition known as "trembles" that may cause death. Lactating mares excrete the toxin in their milk, which they can then pass to their foals.

Signs of White Snakeroot Poisoning

Horses which ingest the plant will develop signs of poisoning within 2 days to 3 weeks. The effect of consumption of white snakeroot is cumulative. Horses may die from eating a large amount of the plant at one time, or from eating small amounts over a long period of time.


  • Trembling
  • Sluggishness
  • Depression
  • Slight Incoordination
  • Sweating
  • Stiff Gait
  • Heart Failure
  • Jaundice
  • Listlessness
  • Teeth Grinding
  • Inability To Swallow
  • Sudden Death


MECHANICAL CONTROL: The best way to reduce the number of the plants is to pull them out by the roots and burn them; the best time to do this is in September, when the plants are more easily identified by their white blossoms. If the plants are pulled after a hard rain while the ground is soft, the shallow roots come out readily. Improving drainage might also help control this plant.

CHEMICAL CONTROL: Triclopyr + 2,4-D (Crossbow®) at 1 to 2 qts/A will provide 80% control. Dicamba products provide about 80% control at 1 to 1.5 pts/A. Spot applications of glyphosate at a 2% v/v solution with water can also provide good control.