Spotted knapweed was first identified in southwest Missouri about 15 years ago, and it is still a threat to area fields according to Eldon Cole, a livestock specialist with University of Missouri Extension.
"I first noticed the pretty purple to pink flowers along a road just south of Mt. Vernon in 2002,” Cole said. “It is hard to say just when it arrived, but some say they had seen it in the 1990's in south central Missouri.”
University of Missouri Extension faculty, the Missouri Department of Transportation and the Missouri Conservation Commission have teamed up to minimize the spread of the short-lived perennial or biennial.
The primary location for most of the knapweed in the state is along roads and railroads.
"Luckily, so far, the encroachment of knapweed into pastures and hayfields has been fairly slow,” Cole said. “Timely mowing reduced but won't stop it is spread.”
The best control, according to Cole, is by several herbicides applied to the plants in the rosette stage of growth. This stage may occur in the fall or early spring or even when the plants are in the bud to early bloom stage in the summer.
"The knapweeds I've seen are running ahead of schedule in maturity this year,” Cole said. “Normally they bloom around the tenth of June but be alert for blooms this year in late May. It is important to keep your guard up for this weed that is extremely invasive."
According to Cole, the blooming plant is easy to spot and even though it is rather attractive, it is on Missouri's noxious weed list.
"If you buy hay, be extra careful and look at the hay field before it is cut making sure it does not have spotted knapweed in it," Cole said.
University of Missouri Extension centers have, or can order, a new Weed and Brush Control book, IPM 1031. The 163-page book has outstanding pictures of many weeds and woody brush species along with recommendations for controlling them.
For more information, contact any of the MU Extension livestock specialists in southwest Missouri: Eldon Cole in Lawrence County, (417) 466-3102; Andy McCorkill in Dallas County at (417) 345-7551; Dr. Randy Wiedmeier, in Howell County at (417) 256-2391; or Dr. Patrick Davis in Cedar County at (417) 276-3313.