Cereal rye (Secale cereale L.) cover crop performance in Minnesota: evaluating weed suppression, seeding rate, termination timing, and profitability

Abstract

Herbicide-resistant weed populations pose significant challenges to traditional weed management, emphasizing the need for integrated weed management strategies. This dissertation explores the use of cereal rye (CR) cover crops as a sustainable weed management tool in Minnesota, addressing the limited data on the biomass required for effective weed suppression and its effects on crop yields. This study assesses the effects of CR on weed emergence patterns and evaluates the influence of seeding rates and termination timings on weed control and crop yields in corn-soybean rotations and continuous corn systems. The results indicate that CR effectively suppresses common weeds in the Upper Midwest. The CR affected soil moisture and temperature; however, these changes had minimal impact on weed emergence, except under water-limiting conditions, where enhanced soil infiltration and reduced evapotranspiration in CR treatments led to earlier weed emergence compared to no-CR treatments. Cereal rye seeding rates did not impact CR biomass, weed suppression, or cash crop yields, suggesting that the lowest seeding rate is the most cost-effective option. In the silage corn-soybean rotation, optimal weed control and soybean yields were achieved by planting soybean in mid-May and terminating CR either at planting with a preemergence (PRE) herbicide or seven days after planting. In continuous corn systems, early planting with CR termination at planting, with or without PRE, provided the most optimal results for weed control and yields. Gross profit margins (GPM) with CR were comparable to conventional practices when seeded at 67 kg ha⁻¹ and terminated seven days after soybean planting, with similar or even lower risk. Although GPM was higher for conventional systems in continuous corn, risk was reduced with CR termination at planting or seven days before planting. These findings provide Minnesota growers with practical recommendations for integrating CR to improve weed management and maintain profitability.