For independent research agronomist Jim Stute, the appearance of glyphosate-resistant giant ragweed, waterhemp and marestail on his East Troy, Wis., farm was alarming. But it was also an opportunity — an opportunity to test the ability of cover crops to suppress marestail and other troublesome weeds and reduce reliance on glyphosate

“The problem with these weeds is that they’re prolific seed producers, they have a wide window of emergence and they’re highly out-crossing, which means they crossbreed,” Stute says. “So you can do everything right on your farm, but if resistant pollen blows in from your neighbor’s farm, you can suddenly end up with a resistance problem.” 

Trial Design

In the fall of 2020, Stute set up randomized complete block plots in four locations with the objective of evaluating the effectiveness of no-tilling soybeans green into a VNS (variety not stated) cereal rye cover crop in terms of suppressing weeds. Enlist soybeans were planted in all locations and treatments. 

For the trial, he established six treatments: 

1. No cereal rye seeded in the fall. A burndown (glyphosate plus LV4) with residual herbicide (sulfentrazone plus cloransulam) was applied in the spring prior to no-tilling soybeans. 
2. No cereal rye seeded in the fall. A burndown (LV4) with residual herbicide (sulfentrazone plus cloransulam) was applied after planting soybeans. 
3. Cereal rye seeded at a low rate (40 pounds per acre) in the fall and terminated (same herbicide program as the control) May 6 prior to planting soybeans.
4. Cereal rye seeded at a high rate (80…