Sudangrass is proving to be a worthy contender as a summer smother crop, according to University of Illinois (U of I) research on Canada thistle.

Its secret? “Sudangrass gets very tall; it outcompetes the thistle for light,” says U of I weed scientist John Masiunas. “Sudangrass creates shade so photosynthesis cannot occur in the thistle. In our test plots, primarily in the northern part of Illinois, we've seen 95% control.” Farmers can plant cash crops the following year in a patch that had been infected with Canada thistle.

But sudangrass has to be seeded the first couple of weeks in June, he says. “If you get much past mid- to late June, sudangrass is not able to compete adequately because the thistle grows rapidly in that time period.”

Masiunas also recommends mowing and tilling the weed – to disrupt its life cycle and keep energy from its roots – before planting the grass. Mow sudangrass to keep it from reseeding itself and control the amount of residue.

The past three summers, Dan Anderson, research specialist, has worked with nine to 20 farmers, looking for environmentally friendly ways to control Canada thistle. Funding came from Sustainable Agriculture Research and Education (SARE).

“The farmers I’ve been working with are primarily in the northern part of Illinois,” Anderson says. Because of the weed’s adaptation, Canada thistle needs a longer day, so it’s not as much of a problem in southern Illinois, Georgia, Mississippi or Alabama.

“I’ve seen some horrible fields in northern Illinois, just full of thistle. Sudangrass was planted on patches of ground where Canada thistle was prevalent, some larger patches and some smaller.

“What we’re aiming at is to eliminate a problem in patches that occur in a field. Our purpose is not to manage Canada thistle on 100 acres but in areas that might be 100 square feet,” he says. “The hope is that the farmer would catch the Canada thistle in a relatively small patch in an intensively managed farm.”

Fields more heavily tilled won’t have as severe cases of Canada thistle. Farmers with reduced tillage who stay on top of the weeds may have small thistle patches.

Sudangrass can also be grazed, Anderson says.

Conventional farmers might use sudangrass as part of an integrated pest management approach if they’re trying to diversify their management strategies, Masiunas says. “You’re generally not going to get 100% control with any type of herbicide that you can use against Canada thistle — 95-98% control is about the best you’ll get with the best application of herbicides. And we’re getting a similar level of control with sudangrass.”

Farmers in the weed project are paid $250 at the beginning of the study and the same amount after they submit a report. Check here for photos of the farms and results.