Farmers are being encouraged to rethink their herbicide strategies as waterhemp and other persistent weeds continue to challenge control efforts in high-residue cropping systems, according to a May 13 announcement. Extension weed scientists say that even when growers follow recommended preemergence practices, residue from heavy corn stalks or thick cereal rye covers can limit the effectiveness of herbicides.
Tom Peters, Extension agronomist and weed control specialist for North Dakota State University and the University of Minnesota, said, “Every year, we have some situations where we get less than expected control of weeds for various reasons, and I’ve come around to appreciate the impact that residue can have on our success.” He added during the 2026 Field Notes program that assumptions about rainfall washing herbicides into the soil do not always hold true. “I would argue that some of our performance challenges have been related to those herbicides sticking to the residues,” Peters said.
Eric Yu, a regional crops Extension educator who conducted graduate research at the University of Minnesota, measured how much product residue intercepts herbicides. Yu said, “We were seeing about a 50% reduction in the amount of product that reaches the soil compared to our control plots. Yet despite that 50% reduction, we were seeing still significant weed control, specifically waterhemp control.” He emphasized that farmers should account for residue but continue using strong preemergence products.
Researchers at the University of Wisconsin-Madison recently evaluated which single-active-ingredient corn and soybean herbicides provide residual waterhemp control in high-biomass cereal rye environments. The study found several effective options for both crops. The researchers also noted timing restrictions with certain products such as flumioxazin and metribuzin when used on soybeans.
Peters advised growers: “Start the season with pre products, observe your results and then decide what the best postemergence program is.” Practical steps include ensuring soil contact for applied chemicals by managing excess crop residue before planting; selecting appropriate products and rates; and tightening application windows since small waterhemp is easier to manage than larger plants.
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