INTEGRATED APPROACHES FOR GIANT RAGWEED (AMBROSIA TRIFIDA L.) MANAGEMENT IN WISCONSIN: CEREAL RYE COVER CROP, SOYBEAN PLANTING STRATEGY, AND FARMER AND CROP CONSULTANT PERCEPTION

Abstract

Giant ragweed (Ambrosia trifida L.), known for its early emergence, aggressive growth, and propensity to evolve herbicide resistance, is a significant challenge in the US Midwest corn- soybean production systems. Effective management of this weed is crucial as it can severely impact crop yields and farming sustainability. Integrated weed management strategies are essential to mitigate the adverse effects of giant ragweed on crop production. Cover crops, particularly cereal rye (Secale cereale L.), provide weed suppression and soil health improvement. Adoption of cover crops can enhance water retention, reduce soil erosion and nutrient losses while suppressing weed establishment and growth. Optimizing the use of cover crops in tandem with other agronomic management practices is essential for maximizing their benefits. Research was conducted investigating multi-tactic giant ragweed management strategies incorporating cereal rye cover crop, soybean planting time, and use of pre-emergence soil residual herbicides. Moreover, farmer and crop consultant perceptions regarding cover crop adoption for weed suppression in Wisconsin were assessed. Conducted over two years in Wisconsin, the first field study quantified the biomass of cereal rye necessary for effective suppression of giant ragweed (Chapter 1). The study demonstrated that 3.8 and 4.8 Mg ha⁻¹ of cereal rye biomass reduced giant ragweed biomass and density by 50%, respectively, establishing a relationship between cover crop biomass and giant ragweed suppression. The second study conducted in Wisconsin and Nebraska explored the impact of soil management practices, soybean planting times, and preemergence herbicide application on giant ragweed dynamics and soybean yield (Chapter 2). Results revealed that the timing of control is crucial in Wisconsin due to the extended emergence window of giant ragweed, with delayed soybean planting reducing giant ragweed density in season but also potentially lowering yield.

Preemergence herbicides improved giant ragweed control and protected soybean yield in both states. Conversely, in Nebraska, where giant ragweed exhibits a shorter emergence window, the timing of soybean planting and control measures was less critical, indicating higher flexibility for controlling this weed. Wisconsin farmers and crop consultants were surveyed to assess current cover crop management practices and perceptions (136 respondents; chapter 3). Waterhemp [Amaranthus tuberculatus (Moq.) Sauer] and giant ragweed were identified as the most troublesome weeds in Wisconsin corn-soybean production systems. Moreover, 90% of respondents use herbicides for cover crop termination, with a majority acknowledging the benefits of cover crops for weed suppression (68%), water retention (85%), and soil erosion reduction (98%). Collectively, these studies emphasize the potential of integrating cover crops, planting strategies, and informed management practices for effective giant ragweed management. The insights documented in these chapters offer valuable guidance for developing more sustainable weed management programs, enhancing soil health, and informing policy and educational efforts in the US Midwest and beyond.