Musk thistle (Carduus nutans L.) is a serious weed found in pastures, roadsides, conserva­ tion reserve acres, and other noncultivated areas across Iowa. This weed infests more than three million acres in the state. Because the state of Iowa classifies musk thistle as a noxious weed, landowners must control any plants of this species present on their property. It is estimated that Iowa farmers spend more than $5 million annually to control musk thistle. Currently, the primary control method for musk thistle involves the use of herbicides.