Open plains, prairies, open woodlands, waste places.
Sheep are most commonly affected, cattle, horses rarely.
Sneezeweed - Helenium amarum
Glycosides and sesquiterpene lactones are present in all parts of the plant. These bitter compounds cause irritation to the mouth and digestive tract resulting in salivation, vomiting and diarrhea. Lactating animals eating bitterweeds may have bitter-tasting milk.
The most toxic species is Helenium microcephalum - smallhead sneezeweed - as little as 0.25% body weight of mature green plant is lethal to sheep.
Similar toxic sesquiterpene lactones are found in the closely related bitterweeds of the genus Hymenoxys.
Depending on the species, the sneezeweeds are annual or perennial herbs. Stems are erect and often branched upward. Leaves are simple, alternate (H. amarum has thin leaves 2mm wide, while H. autumnale has broad leaves with winged stems). Flowers are showy, produced on slender stems with yellow ray flowers and yellow disc flowers. Some species (H. microcephalum) has purple-brown disc flowers.
The most important toxic species are:
Helenium amarum - bitter sneezeweed
H. autumnale - common sneezeweed
H. flexuosum - purple headed sneezeweed
H. microcephalum- small-head sneezeweed
Dugaldia hoopesii- orange sneezeweed.
Salivation, vomiting and diarrhea lead to dehydration, weakness, recumbency and death. Inhalation pneumonia will cause difficulty in breathing and coughing. Death usually occurs when inhalation pneumonia develops.
Muscle tremors, weakness.
Remove animals from the source of the bitterweed and provide nutritious food and water.
Coughing, increased respiratory rate secondary to inhalation pneumonia.
Most animals will not eat the bitterweeds unless they starving.
1. Dollahite JW, Hardy WT, Henson JB. Toxicity of Helenium microcephalum (small head sneezeweed). J Am Vet Med Assoc 145:694-696, 1964.
2. Dollahite JW, Rowe LD, Kim HL, Camp BJ. Toxicity of Helelnium amarum (bitter sneezeweed) to sheep. Southwest Vet 26:135-137, 1973.
Control of Sneezeweeds
Sneezeweeds and Bitterweeds can be effectively controlled with 2,4-D, picloram, clopyralid, or metsulfuron applied from fall to early spring before flowering when the plant is actively growing. Follow label directions for application rates and precautions for handling herbicides.