Knapweed in a field.

Constant vigilance against musk thistle and spotted knapweed are needed, says Extension specialist

A drive around southwest Missouri this time of year could leave the impression that weeds are taking over pastures and roadsides.

This is especially apparent when it comes to musk thistle, and the newest troublemaker, spotted knapweed, according to Eldon Cole, livestock specialist with MU Extension

“The thistle and knapweed are in full bloom now and show up easily as you drive down the road,” said Cole.

Both spotted knapweed and musk thistle are on Missouri’s noxious weed list. Not much can be done at this time of the year as a control of either weed pest.

“Herbicide treatment in the fall is effective on both. Another good time to treat is April and early May,” said Cole.

Two thistles

Most people are familiar with musk thistle and realize it causes problems in pastures, hay fields and about anywhere it becomes established.

“Cattle refuse to graze near musk thistle, it spreads easily and it annoys neighbors when not controlled,” said Cole.

Spotted knapweed is fairly new to southwest Missouri, but is spreading rapidly, according to Cole.

MU Extension specialists, Missouri Department of Transportation personnel and Missouri Department of Conservation staff have been working to acquaint landowners with the highly invasive weed.

“Persons not familiar with it may see the attractive purple or lavender blooming plant along the highway and not realize the threat it poses to neighboring pastures,” said Cole.

Knapweed was first identified in southwest Missouri in 2002. Most of the early sightings were along major highways and railroads.

“It seemed most evident where the earth had been disturbed from road construction or the laying of fiber optic cable. Those areas were reseeded and mulched and the knapweed seed likely was brought in that way from northern and western states,” said Cole.

Biological controls

Biological control by the introduction of musk thistle weevils back in the 1960s and ’70s has proven useful, according to Cole.

“Although there are still lots of thistles this year it’s apparent the weevil will not completely destroy them but do help to some extent,” said Cole. “A couple of different types of natural enemies of spotted knapweed have been released in the region but their survival and effectiveness have not been determined yet.”

The knapweed problem is still minor in many locations. But, Cole says if the last two year’s spread is any indication, landowners need to know what it looks like and attempt to keep it off their property.

“Knapweed is capable of reducing forage yields when it invades your pasture and hay fields which will reduce carrying capacity. Ultimately, the economic impact will be severe,” said Cole.

Information about spotting knapweed and musk thistle isavailable on the MUExtension website.

 

 

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