White snakeroot, Eupatorium altissima (formerly known as Eupatorium ruguson) is found in shaded environments from the Rocky Mountains east and from Canada south through Texas. It thrives in established timber and woodland areas, riparian waterways, and windbreaks that are shady and often moist due to high levels of organic matter in the soil. It does not persist in sunny cultivated areas.
White snakeroot is a herbaceous perennial that normally grows to 3 ft. but can grow as tall as 5 ft. It has short branches with a smooth stem and leaves that are pointed ovals with sharply serrated edges. The leaves are arranged oppositely on the stem and branches. The roots are fibrous with rhizomes and very shallow. Reproduction takes place through either seeds or the rhizomes. The flowers are arranged as a flat topped or domed cluster of small white flowers, with each flower producing a single seed. Flowering takes place during the late summer.
White snakeroot is generally not aggressive enough to be considered a serious weed problem, but if left unchecked for extended periods can become more than just a nuisance. White snakeroot can become a problem if livestock consumes it. White snakeroot has been found to be toxic to all mammals that it has been tested on. All parts of the plant are considered toxic. Livestock may die from eating large amounts of the plant at one time or consuming smaller amounts over a longer period of time. Symptoms of poisoning include muscle tremors and weakness, constipation, and possible death. Nursing livestock that consume white snakeroot will transfer the toxin to their offspring, again resulting in the possible loss of the offspring.
The transfer of the toxin through milk can be an issue for people who consume milk from livestock that have grazed on white snakeroot. This is known as milk sickness. In the early 1800's, milk sickness resulted in the death of thousands of people, most notably, Abraham Lincoln's mother in 1818. Prior to the discovery of the plant's toxic effects, milk sickness was thought to be a late summer/early fall infectious disease and also known as milk fever.
Control of white snakeroot may not be easy. The use of herbicides, both broad-spectrum, such as 2,4-D, and selective herbicides, such as glyphosate are toxic to other neighboring plant species so care must be taken when applications are made. Mechanical control, which includes hand pulling, is most successful when the plants are as young as possible prior to establishing their fibrous roots systems that include rhizomes. Once the rhizomes have developed, control becomes much more difficult. Rhizomes that detach from the roots when the plants are pulled can develop into new plants. Cutting the plants back prior to or during flowering but before seed development takes place will hamper seed development and reduce the amount of seed in the soils seed bank.