Knapweed along a county highway.

It has been 10 years since spotted knapweed was first identified in southwest Missouri. The first three or four years after being noticed it didn’t seem to be spreading, according to Eldon Cole, a livestock specialist with University of Missouri Extension.

“But in the past few years, this noxious weed has shown up in increasing amounts in new places around southwest Missouri,” said Cole.

Originally, spotted knapweed was seen in road excavations, along railroad tracks and in areas where fiber optic cable had been placed.

“It’s been felt the seed that was used to recover those areas contained the knapweed seed. It’s also possible the straw mulch could have had seed in it,” said Cole.

The recent spreading can be attributed to natural means as each plant produces thousands of seeds. Additionally, hay baled locally now may contain some seed. Much hay was brought into this area in 2011 from northern states and it could be contributing to the spread.

University of Missouri Extension, Missouri Department of Transportation and the Missouri Department of Conservation have cooperated in teaching landowners what knapweed looks like, where it’s located in the state and how to control it.

Spotted knapweed is now on Missouri’s noxious weed list.

Knapweed control is not difficult. There are several herbicides that are effective when used in October or in the spring. Regular mowing can keep the plant from producing seed. Spring applications should be made before the plant bolts.

“The unusually warm spring has resulted in more rapid development of the plants this year. Rather than blooming around June 10, as in the past, they’ll likely bloom in mid- to late May this year,” said Cole.

As the plant’s pink to purple bloom develops they are more easily noticed. This aids in their identification.

“It’s important to identify these locations so they can be treated in the fall. You’ll also be able to avoid these spots in the field if you’re baling hay,” said Cole.

MU Extension, MoDOT and the Missouri Department of Conservation have cooperated on a biological control project with weevil releases in areas heavily infested with knapweed. These control methods have given some control in northern and western states.

“The Missouri releases were made almost three years ago. Looking at those sites this year should help evaluate the weevil’s survival and reproduction rate,” said Cole.

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