Planting cover crops can be an effective weapon in the battle against weeds. There is a learning curve, however.
Species, planting methods, timing and other factors can vary in efficacy. For those getting started, Adam Dahmer has a few tips.
“Cereal rye and soybeans is front and center,” said Dahmer, who owns Advanced Cover Crops in Marion, Illinois. “That’s the best way to do it.”
One key is plant population for maximum shade, which helps prevent growth of winter annuals.
“They also have to put out enough to obtain weed control,” Dahmer said. “They’ll have the canopy, and cereal rye suppresses weeds. Hairy vetch does well. But for guys just beginning, cereal rye would be best thing.”
University of Illinois weed scientist Aaron Hager also said cover crops are a good tool in battling weeds. He points to stand and coverage as critical factors.
“Without a doubt, cover crops can show suppression of winter annuals,” Hager said. “An important factor is stand establishment. Is it dense enough to suppress the weeds? How much suppression is there for summer annuals? That plays a role.”
Dahmer is partial to cereal rye, especially for beginners, for a number of reasons.
“We get it established well, and there is a good amount of biomass on top,” he said. “If we’re talking weed control, it needs to get a fully mature state for weed suppression. Waterhemp doesn’t like competition to start with, so if you put dense cover crop out there it’s not going to compete hard for it.”
Using cover crops or planting winter wheat as a cash crop helps with suppression of winter annuals, but not always with summer annuals, Hager said. And a trend in recent years of soybean growers planting their crop earlier than in the past may limit the benefit.
“We can make a stand of rye work quite well even for suppression of summer annuals. But you have to let it go until it’s about 90%. Many farmers are not willing to let it go that long,” Hager said. “There’s a trend or movement of acres of soybeans going in very, very early. We’re talking April planting of soybeans now. There’s not much biomass to give us suppression of summer annuals.”
One alternate method of natural weed control is interseeding. Researchers at Southern Illinois University are looking at a project in which wheat is seeded in the spring along with soybeans. The experiments continue research first introduced years ago by the late Southern Illinois University weed scientist George Kapusta, who also did pioneering work in no-till.
While Dahmer is keen on cereal rye, especially for novice cover crop practitioners, he also promotes hairy vetch as a cover that provides good weed control.
“It does have a higher seed cost,” he said. “And it’s probably the most to manage as far as your equipment capabilities. It’s designed more for guys who know exactly what they want to do.”