Knapweed along a county highway.

The Missouri Department of Transportation said Monday it is working to control the growth and spread of spotted knapweed on its roadsides this season. The purple-flowered perennial was declared a noxious weed last year in Missouri.

Spotted knapweed blooms from June to October, and it releases a chemical called Catechin to kill surrounding plants. It is an extremely aggressive invader that typically occupies dry meadows, pastureland, stony hills, roadsides and floodplains of streams and rivers.

The south central district of MoDOT is using various herbicide treatments and bio-control to curb the growth and spread of this noxious weed.

Bio-control is the use of a living organism to control a pest or invasive plant and has been used by the south central district since 2008. It is an environmentally friendly method of weed control, as the insects only feed on the weed they are targeted for. All bio-controls utilized by MoDOT are approved by the U.S. Department of Agriculture’s Animal Plant Health Inspection Service prior to release.

For spotted knapweed management, MoDOT is utilizing releases of both the Flower Head Weevil and the Root Weevil. They are the natural predators of knapweed, and are “host specific” – they will only feed on the weed they are targeted. The Flower Head Weevil feeds on developing knapweed seeds, while the Root Weevil attacks the plant’s roots. Research has shown that when used together, these insects can reduce knapweed density by up to 99 percent.

According to Roadside Manager Justin Hills, MoDOT is using an integrated approach by timing herbicide applications and biological releases that will not affect desirable vegetation on roadsides or neighboring landowners.

Leave a comment

Leave a Reply