Knapweed competes with rangeland grasses and forbs, reducing forage production to near zero in areas where the weed is well established. The plant has little grazing value and is avoided by livestock and wildlife when other forage is available. In the rosette stage the plant looks very much like a dandelion. As the main stem of the plant starts to shoot up, or bolt it can grow to be 1 to 3 feet tall. The plant has a deep taproot.
Flowers are generally white, but sometimes pink or lavender.
Diffuse knapweed can produce up to 1,200 seeds per flower stock. This assists the plant in taking over lands very quickly. Upright stems have numerous spreading branches, and a tumbleweed mobility when broken off. Mature plants are easily caught and transported on all types of farm, ranch, and recreation vehicles. This is commonly the plant you will see being carried along roads on the undercarriage of cars and trucks.