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Spotted Knapweed, Other Invasive Weeds a Growing Hassle For Southwest Missouri Landowners


An enemy to landowners and farmers is running rampant throughout pastures in southwest Missouri. And as KSMU’s Samuel Crowe tells us, many residents of rural counties remain unaware of its existence.

[Sound: rain falling along highway]

Along highways and pastures in the Missouri Ozarks, one may spot what seems to be some pretty purple wildflowers swaying in the warm summer breeze. But don’t be fooled; most likely it’s spotted knapweed, one of the mostinvasive plant species on the block. First discovered in the area in 2002, its seeds were likely introduced to the soil from mulch brought in from northern states. That mulch that was used during local road and utility construction. John Hobbs is an Agriculture and Rural Development Specialist for the University of Missouri Extension in McDonald County. He took me out to the county library on a rainy morning to observe the pest.

“This is the spotted knapweed in its latter stages. You can see the seed has matured; the brown seed head, the flowers are fading and have fell off. It gets rather stemmy, the leaves get a little bit withered. It kind of looks like a good native wildflower,” he said.

The problem with spotted knapweed, and other invasive weeds like muck thistle, is that they contain toxins that kill off other plant species around them. This means that cattle’s food supply can potentially be destroyed,and so can hay fields. The economic impact is potentially devastating. Fortunately, the MU extension is doing its part to educate landowners about the weeds.

“We have different agronomy programs. With the cooperation of the USDA, the NRCS, the soil and water districts and the University of Missouri Extension, we have grazing schools. And at those grazing schools we talk about weed problems and we usually bring a sample of a spotted knapweed in so they can see what it looks like, so they at least know what they’re looking for in the future,” he said.

The extension office also teaches different methods of weed control and removal. Root and flower weevils are tiny insects that eat at the roots and immature seeds of the thistle and knapweed—those have beena useful tool to help contain the weeds. Herbicide spray treatment is used to kill off the weeds. Hobbs says it’s up to the individual landowner to do his or her part to prevent the weeds from dominating southwest Missouri pastures, not an easy feat considering each individual knapweed plant contains a thousand seeds, while a single muck thistle contains ten thousand.

“With the weevils, it’s strictly to help control, not eradicate. And the constant vigilance of the local landowner by hand pulling the thistle, the stray thistles that come up, or if you have a large amount to spray, is about the only way you’re going to be able to keep your farm clean. We’re in the beginning stages of a large problem,” he said.

Hobbs says the best times of year for landowners to spray the invasive weeds are in the spring, when the weeds are at their early growth stages, or in the fall, when the seeds begin to germinate. The weevils are active in the summer and will not survive a dose of herbicide. But if the right steps are taken, says Hobbs, it’s the spotted knapweed and muck thistle that won’t survive. For KSMU News, I’m Samuel Crowe.