Spotted knapweed has become a significant weed issue in the Ozarks during recent years, according to Tim Schnakenberg, agronomy specialist, University of Missouri Extension.
“Seen mostly along roadways and ditches, spotted knapweed has begun to creep into pastures and hayfields. It continues this year to be a serious concern because once the seed is spread, it can overcome and dominate other vegetation.
In fact, the invasive nature of spotted knapweed got it added to the noxious weed list in the state of Missouri.
According to Schnakenberg, spotted knapweed has the ability to produce a toxin in the root zone, called catechin that will kill surrounding plants. On average, a single knapweed will also produce 1,000 seeds per plant, but some large plants have been known to produce up to 25,000 seeds.
These seeds can be propelled up to a yard away from the mother plant and can remain dormant in the soil for up to 8 years.
“Spotted knapweed is especially a concern when mature plants are harvested in hay fields and fed elsewhere or when it is mowed and the seed drops off the mower deck in another location. These situations can propagate the pest quickly to other farms or other locations around the farm,” said Schnakenberg.
As with any invasive weed, prompt action should be taken if the weed is found on your property. At the very least it should be kept from going to seed.
“The most practical approach is to spot spray the weed before it flowers with products such as Milestone, Grazonnext, Tordon, Grazon P+D, Gunslinger or Hired Hand. None of these products will kill the grass around where the weed is growing,” said Schnakenberg.
Several attempts to incorporate biological control have been done in southwest Missouri.
University of Missouri Extension, Missouri Department of Transportation, and in some areas the Missouri Department of Conservation, has been active in releasing knapweed rosette and flower head weevils that will attack the problem.
“These weevils will not fully overcome the weed but it is believed, based on 30 years of experience with them in western states, that they have the potential to lower the infestation levels. It will be several years before results will be noticed but release sites are currently being monitored for activity,” said Schnakenberg.
Spotted knapweed is found growing along many roadsides in the area. Its dense foliage is grayish green and it can grow two to four feet tall before it flowers. One plant may produce one to twenty stems. Pink thistle-like flowers usually come out in June and July.
