Common Tansy is a List B species on the Colorado Department of Agriculture list. List B species require suppression management techniques at the minimum. Common Tansy is an ornamental, perennial shrub-like plant that was introduced for landscaping, and quickly spread to pastures, stream banks and roadsides. It spreads through seeds and its root system. It is toxic to livestock and humans if ingested. For more information on plants, go to www.weldweeds.org.