Description, Location and Control Options

“The weed has been found along Highway C north of Seymour, along Highway 60 east of Seymour, along Highway A between Marshfield and Highway 60, and along the railroad right-of-way through Marshfield,” said Bob Schultheis, natural resource engineering specialist with University of Missouri Extension in Marshfield.

Spotted knapweed is a short-lived perennial plant that grows 2-4 feet tall. It forms a rosette the first year and then sends up a flower stalk the second year. The leaves, which are rather sparse on a hard and woody stem, have a pale green color. The weed blooms in mid-summer and the blooms are pink to purple in color and rather attractive. The weed reproduces solely by seeds, and the weed is a prolific seed producer with 1000 or more seeds per plant.

“Now, and in the next few years, special efforts need to be made to keep spotted knapweed in check while it is only along roads and not out in pastures,” said Schultheis. If not controlled, it can rapidly invade pastures and fields and cause a serious decline in forage and crop production.”

According to Tom Hansen, Extension agronomy specialist, several herbicides are effective at controlling spotted knapweed when used in a timely manner. In order of effectiveness are Milestone at a 5-ounce per acre rate, Tordon 22K at 1 pint per acre, or Grazon at 4 pints per acre. They are best applied at the bud stage in the spring or at the rosette stage in the fall.

For more information, contact the Webster County Extension Center at 417 859 2044 or by e-mail at websterco@missouri.edu, or Tom Hansen at 417-862 9284.