Results from our proposed research will: 1) quantify the effect of extreme precipitation events on residual herbicide efficacy; 2) evaluate the potential for cover crops to enhance weed control in response to extreme precipitation; and 3) improve the capacity for IWM to increase agricultural resilience to a changing climate by preventing pest outbreaks associated with extreme weather, thus increasing overall yield stability.
Results from the research objectives will be distilled into a general ‘rule of thumb’ to aid farmers and agronomic professionals in understanding roughly how much precipitation will result in loss of weed control efficacy of residual herbicides varying in solubility, with inferences drawn to other residual herbicides.
Project results will be disseminated to a wide audience through multiple mechanisms, including: 1. Extension events and workshops; 2. factsheet; and 3. educational video.

Updated December 31, 2023:

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Often, integrated management tactics are highlighted as the best approach to increase the resilience of a farming system to weather variation and extreme scenarios. However, our research shows that the integrated approach (cover crop surface residues combined with residual herbicides) did not improve weed control when extreme precipitation events occurred, and may have lowered weed control efficacy in certain scenarios (e.g. when more soluble residual herbicides were used, such as Outlook). This research highlights the importance of evaluating integrated approaches across a range of environmental conditions and weather scenarios. However, it is important to note that even within our extreme rain treatments, we still saw that residual herbicides remained overwhelmingly effective. Among the Group 15 herbicides, both Zidua and Dual remained effective, providing over 80% control of pigweed, however control of foxtail was more variable especially when combined with a cereal rye cover crop. With both Outlook and Dual, we saw greater loss of efficacy with greater intensity of extreme rainfall (5x1) compared to greater frequency (2.5 x 2), and this was exacerbated when combined with cereal rye surface residues.