By Scout Nelson
Pigweeds, including Palmer amaranth, waterhemp, and smooth pigweed, are some of the most challenging weeds to control in row crop systems. Due to their rapid growth, high seed production, and herbicide resistance, particularly to ALS, glyphosate, and PPO inhibitors, managing these weeds has become a priority for agricultural systems. Over the years, the reliance on herbicides has led to the evolution of herbicide-resistant pigweed populations, further emphasizing the need for integrated weed management strategies. One such strategy is the use of cover crops.
A meta-analysis by the University of Nebraska–Lincoln, reviewing 41 studies conducted across the U.S. and Canada from 1994 to 2024, shows that cover crops significantly reduce pigweed density and biomass. The study found that cover crops can reduce pigweed density by up to 58% in the early season and up to 44% in the late season. Grasses and mixtures were found to be most effective, reducing pigweed density by 60% in early season and 47% in the late season.
One of the key takeaways from the data is that higher biomass from cover crops leads to better weed suppression. Dense cover crop stands create a thick mulch layer that reduces sunlight penetration, thus inhibiting pigweed emergence. Additionally, certain cover crops, like cereal rye, release allelopathic compounds that suppress weed growth.
In Nebraska, where cover crops are already beneficial for soil health, this research highlights their role in managing herbicide-resistant pigweeds. The study suggests planting cereal rye by late September for the best biomass production and pigweed suppression.
Photo Credit:palmer-amaranth-united-soybean-board
Categories: Nebraska, Crops, Education