Black Henbane (Hyocyamus niger) Revisited
Introduction

Photo: Jane Mangold, MSU.
Black henbane, less commonly known as fetid nightshade or insane root, is an annual to biennial plant that grows in pastures, meadows, and roadsides, and has been gaining attention in Montana. For example, since the February 2014 Weed Post the number of counties including black henbane on their county noxious weed list has more than doubled. Counties include Beaverhead, Big Horn, Broadwater, Carter, Deer Lodge, Glacier, Golden Valley, Meagher, Musselshell, Powder River, Powell, Ravalli, Rosebud, Stillwater, and Yellowstone.
Identification
Rosettes are large and generally have toothed to incised leaves that are covered with fine hairs. The plant can grow up to 3 feet tall. From June-September, plants form tubular, light yellow flowers that are five-lobed, 2 inches wide, and have purple veins and throats. The flowering stalk with vase-shaped fruits is distinctive. Stem leaves are alternate, dentate to lobed, have a prominent white mid-vein, and are up to 8 inches long by 6 inches wide. The plant has a foul odor due to dense glandular hairs on leaves and stems.
History and Impacts

Photo: Jane Mangold, MSU.
Black henbane is native to Europe and northern Africa where it was cultivated for its medicinal qualities. There is folklore about black henbane, including associations with witchcraft, shape shifting, rituals, and Greek mythology. It was likely introduced to the United States in the 17th century as a medicinal and ornamental plant. Black henbane has since escaped cultivation and spread throughout much of the United States, particularly in the Northeast, Midwest and the Rocky Mountains. Despite its medicinal qualities, all parts of the plan contain alkaloids which are toxic to humans and animals if consumed. Livestock avoid black henbane unless other forage is not available. However, dried plants in baled forage remain toxic and may be eaten inadvertently.
Management

Photo: Anne Elliott, Flickr.
Prevention and early detection are the top management priorities. Black henbane thrives with disturbance so avoid overgrazing and other disturbances. Early detection is relatively easy because the tall, distinctive flowering stalks make the plants readily detectable once they bolt. Hand pulling (with gloves) while populations are still small is strongly recommended. If the soil is dry, use a shovel to make sure the thick, fleshy, taproot is completely removed. Because this plant reproduces by seed, pulling should occur before seed set. Plants with mature fruits should be placed in bags to prevent spread. Return to the site a month after the first treatment to pick up missed or late bolting plants and return annually for four to five years, based on the seed longevity. Several herbicides provide control including aminopyralid, dicamba, metsulfuron, and chlorsulfuron. Herbicides should be applied with a non-ionic surfactant at the rosette stage and prior to flowering for best results. For more information, see the MSU Extension publication “Black Henbane: Identification, Biology and Integrated Management.”
Further Information
For more information about this month's weed post, contact Extension Invasive Plant Specialist Jane Mangold. Past posts are available in the Monthly Weed Post Directory.
THis weed post is also available as a printable PDF (345 KB).