Variable weather and implications for herbicide efficacy and yield loss due to weeds

Midwest agriculture is not immune to climate change, as evidenced by increased greenhouse gas levels, more variable and extreme precipitation, and higher average air temperatures. These trends are expected to worsen throughout the 21st century. Variable weather impacts crops, weeds, and their management; however, empirical study of these phenomena has been piecemeal and limited to a handful of site years (e.g. generally 2 to 4). This research was developed to shed light on how future climate variability in the Midwest can affect crop and weed management options and outcomes. A meta-analysis was conducted on a database of >3,000 individual herbicide evaluation trials conducted between 1992 and 2019. Chapter 1 of this dissertation is a review of the literature related to climate change and weed interference effects on corn and soybean production. In Chapter 2 we quantified rainfall and temperature variation on the efficacy of several common preemergence herbicides used individually and in combination on key Midwest weed species. Results demonstrated a rainfall threshold of 5–10 cm within 15 days of application of specific herbicides was required to maximize the probability of acceptable control of the weeds studied. Furthermore, when rainfall fell below this threshold, increasing soil temperatures had either a positive or negative effect on the probability of control depending on the weed species and herbicide treatment combination. Linkages among weather variability, crop management, and weed control on yield and yield loss due to weeds were examined for corn in Chapter 3 and soybean in Chapter 4. Late-season weed control was found to be the largest contributor to yield and yield loss in corn and soybean. Furthermore, inadequate water availability and excessive temperatures during silking in corn, or during seed filling in soybean, exacerbated yield loss from poorly controlled weeds. Planting corn earlier and using a later maturing soybean cultivar were shown to alleviate some of the potential yield losses due to uncontrolled weeds. Current trajectories portend a future with weed control becoming more difficult, driven in part by herbicide resistance, and the weather becoming more variable, driven by climate change. Adapting Midwest corn and soybean production for the future requires considering the significance of weeds and transforming how they are managed.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste