Thistle conditions were ideal for growth across southeast Nebraska this year, according to local weed officials.
“This year, particularly, was a very good year for thistles because of the dry early spring where nothing grew, and then we got that rain and everything took off,” said Saline County Weed Control Superintendent Lyle Weber. “Thistles grow faster than grass, so, naturally, everybody saw.”
There are three thistle species Nebraska considers noxious weeds at the state level: musk thistle, Canada thistle and plumeless thistle, according to Seward County Weed Control Superintendent Tim Kallhoff. He said musk thistle has been the main issue this year.
Not all thistles are harmful, however. Weber noted that some species benefit wildlife and pollinators. For example, tall thistle is native to Nebraska and is popular with bees. Anyone uncertain about a thistle species can contact their local weed superintendent for identification.
Despite some beneficial species, controlling noxious thistles is important.
“If they get overgrown, they will push out desirable vegetation,” Weber said. “Like, in a pasture, if the thistles get thick, you’ll have nothing else growing. If you have, say, cows out there, there’s nothing for them to eat because they won’t eat thistles.”
Thistles are prolific seed producers, and their seeds can remain viable in the soil for years.
Weed superintendents spend part of their time driving roads and searching for thistles in road ditches and pastures. Landowners are legally required to control thistle growth.
As biennials, Weber said thistles are easiest to kill during the rosette stage, when they lie flat on the ground.
“They're hard to find when they're in that stage, because they're so low to the ground,” Kallhoff said. “But, by the time April, May rolls around, they start shooting up into the bulbing stage, and that's also a good time to spray for them before they go to the bud or the flowering stage.”
Chemical control during the rosette stage in the spring or fall is typically the most effective approach. According to Weber, the best and least expensive herbicide option is usually 2,4-D.
In cases where stronger herbicides are necessary, users should be especially careful.
“I’ve known people who spray chemicals with residual, and they’ll go mow it or they’ll bale something, and that residual may still be in that bale,” Weber said. “Then, if you go put it out into a cornfield, and next year you plant beans there, sometimes that chemical will still be there, and your beans won’t grow.”
When temperatures are high, chemicals can also turn into vapor, travel as far as three miles and settle back to the ground, damaging nearby plants.
“Fall is just the easiest time to control them, because your grass isn't tall, so you can see them,” Weber said. “You don't have to use as much chemical, so it's the cheapest. You don't have to worry as much about the neighbors' gardens or the soybean fields or flowers, because they're all pretty much done for the year.”
Unfortunately, many people do not notice thistles until they begin flowering.
“Once they turn purple and they’re mature, even if you spray them, that purple flower is still going to turn white and spread seeds,” Weber said. “Basically, you’re wasting your money if you spray them once they are all purple.”
At that stage, Kallhoff said another option is to cut the heads off and safely burn them or put them in a bag, seal it, and trash it. Then, dig up the remaining plant or spray it with herbicide to prevent regrowth.
“It’s amazing how these plants will try and survive if you just cut the heads off,” he said. “They will actually put more on.”
However, because thistles often occur in large patches, that method is typically not practical. In most cases, landowners must wait until fall to treat them.
Any time uncontrolled growth is found, Weber said he first notifies the landowner. If action is not taken, a 10-day notice is issued. If the thistles remain, Weber will arrange for the control work to be completed and bill the landowner for the cost.
When Weber finds thistles during the summer, he maps the locations and sends letters to landowners in the fall.
Controlling thistles is often a long-term effort. Weber said he revisits areas for several years after discovering a patch to monitor for regrowth.
For weed officials, early detection remains the key to successful control. They encourage people to report thistles to their weed superintendent whenever they see them.
