The Purdue University pasture weed control trial conducted in 2020 at the Scholer Beef Farm in Warren County, Ind., proved that you can take tough weeds out of pastures with today’s herbicides. There are several herbicide options, depending upon whether you have somewhere else to move livestock during application and when and what you intend to interseed into the pasture later.

“Herbicides vary in grazing restrictions and plant-back intervals for various crop species,” says Keith Johnson, Purdue University Extension forage specialist. “It’s important to read the labels for any herbicide you’re considering before choosing it.”

BEFORE TREATMENT: Notice healthy Canada thistles and chicory, with the blue flowers, just before herbicide was applied.

Others assisting in the pasture weed control trial included Ron Lemenager, Purdue University Extension animal scientist, John Scott, Purdue digital agriculture resource specialist, Bill Johnson and Marcelo Zimmer, Purdue weed scientists, and Stacey Songer, a chemical representative for Corteva Agriscience.

Six herbicide treatments were tested in the trial. All of them were effective against key weeds, including Canada thistle. ProClova, a Corteva product still awaiting registration from the Environmental Protection Agency, was less effective against Canada thistle than the other products, but still produced 88% control at six weeks. It was the only product tested that did not kill white clover, a desirable legume in many pastures.

AFTER TREATMENT: Here are the same weeds four weeks after application of DuraCor, a relatively new herbicide for pasture weeds from Corteva Agriscience.

The before and after pictures for DuraCor from Corteva tell the story, Keith Johnson says. Note how lush Canada thistle and chicory are before application, and how they appear four weeks later.

“It may take more than one application in one season to eliminate a perennial like Canada thistle, but applying a herbicide in-season is a good start toward control,” Bill Johnson says.