Integrated weed management in pulse crops

Abstract

The wheat-fallow rotation remains a predominant cropping system in the US Great Plains, with heavy reliance on chemical control for weed management. This reliance has resulted in problematic weed infestations, necessitating the exploration of additional weed management options. Crop diversification with pulse crops such as chickpeas and fava beans offer expanded weed management options and several agronomic and soil benefits. However, these crops are poor weed competitors due to their slow early-season growth. Early season weed management, primarily through pre-emergence (PRE) herbicides, is crucial but is challenged by a lack of tillage and limited precipitation for herbicide activation in semi-arid regions. These PRE herbicides can also be applied in the fall to facilitate activation, thereby maintaining residual activity for controlling weed emergence and enhancing crop competition in the spring. Another cultural method to enhance competitiveness is early planting, which can provide the crop with a head start by allowing it to emerge before weeds. Field experiments were conducted across Montana in 2022 and 2023 to study the effect of fall-applied herbicides and the integration of fall-applied herbicides and planting dates on weed management in spring-planted pulses. The results demonstrate that fall-applied herbicides provide early-season weed suppression and improve crop establishment, with certain combinations (e.g., pyroxasulfone + flumioxazin, dimethenamid + pendimethalin, carfentrazone + sulfentrazone) offering consistent residual activity throughout the season. However, the efficacy of some of these treatments (e.g., pyroxasulfone, simazine, ethalfluralin, dimethenamid) diminishes later in the season, necessitating a follow-up post-emergence herbicide application to manage late-emerging weeds. Additionally, the thesis explored the integration of fall-applied herbicides and planting dates, revealing that early planting provided an additional 20 (3.5) % reduction in weed biomass by allowing the crop to emerge before major weed species. The integration of herbicides and early planting yielded a substantial increase in crop yield compared to the untreated check, demonstrating the potential of these programs to improve weed management and crop productivity in pulse rotations. The results highlight the importance of integrating chemical and cultural weed management tactics for increasing cropping systems' sustainability by integrating pulses in the US Great Plains.