Spotted knapweed is becoming a bigger problem for hay growers, livestock producers and other landowners in parts of Missouri, reports Eldon Cole, livestock specialist with University of Missouri Extension.

The weed was first identified in the southwestern part of the state in 2002, he notes. Most early sightings were along major highways and railroad tracks. Since then, it has been spreading fairly rapidly.

"Persons not familiar with it may see the attractive purple or lavender blooming plant along the highway and not realize the threat it poses to neighboring pastures," says Cole. Knapweed can reduce forage yields and carrying capacity.

"Ultimately, the economic impact will be severe.”

The best bet for controlling knapweed: applying herbicide in fall or early spring. “A couple of different types of natural enemies of spotted knapweed have been released in the region, but their survival and effectiveness have not been determined yet," the specialist says.