Cropping System Redesign for Improved Weed Management: A Modeling Approach Illustrated with Giant Ragweed (Ambrosia trifida)

Abstract

Weeds present important challenges to both conventional farmers who rely on herbicides and organic farmers who rely on cultivation. Data from field experiments indicate that diversifying crop sequences with additional species can improve weed suppression when either herbicides or cultivation serve as primary control tactics. Here, we report the results of modeling analyses that investigated how cropping system diversification would affect the population dynamics of giant ragweed (Ambrosia trifida L.), an annual dicotyledonous species that is problematic in the central U.S. for both conventional and organic farmers. We found that to prevent an increase in giant ragweed density, the minimum control efficacy needed from herbicides or cultivation used in corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) would be 99.0% in a 2-year corn–soybean system, but 91.4% in a 5-year corn–soybean–rye (Secale cereale L.)–alfalfa (Medicago sativa L.) system. Thus, the diversified rotation would be better buffered against less-than-perfect weed control during corn and soybean phases. Further modeling analyses indicated that the weed suppression effect associated with greater rotation length was attributable not only to increased crop species richness but also to greater temporal variation in planting dates. A planting interval variation index (PIVI), calculated as the coefficient of variation in months between planting activities, was strongly associated with the weed suppressive ability of the rotations we modeled and may be a useful metric for designing other cropping systems. Overall, our results indicate that diversified rotation systems that include both annual and perennial crops are likely to be valuable for managing problematic weed species.

Cover crops and weed suppression in the U.S. Midwest: A meta‐analysis and modeling study

“…To prevent an increase in weed seedbanks, reductions in WDEN of 90% (comparable to herbicide effectiveness) are needed (Liebman & Nichols, 2020); our study shows that even with 5 Mg ha −1 of CCBIO, producers are unlikely to achieve this level of weed control, consistent with studies from other areas (Baraibar et al, 2018;Mirsky et al, 2013). Moreover, our SALUS simulations indicate achieving 5 Mg ha −1 of rye CCBIO regularly under typical Midwest production scenarios and climates would be challenging (Figure 2).…”

Crop Diversification for Improved Weed Management: A Review

“…In that case, modeling simulations are used, which will consider all growth and environmental parameters. For example, Liebman and Nicholas [58] modeled giant ragweed (Ambrosia trifida L.) population dynamics in different crop rotation scenarios. They predicted that to prevent an increase in giant ragweed density, the minimum control efficacy needed from herbicides or cultivation used in corn and soybean would be 99% in a 2-year corn-soybean, whereas 91% in a 5-year corn-soybean-rye-alfalfa system.…”

Weed seedbank diversity and sustainability indicators for simple and more diverse cropping systems

“…Cropping system diversification through the use of multi‐species rotations can increase the range of disturbance events and stress and mortality factors that regulate weed population dynamics, and thus can be useful for suppressing weed population densities while reducing the burden of crop protection placed on herbicides and physical weed control practices (Liebman and Nichols, 2020; Teasdale, 2018; Weisberger et al , 2019). Diversified crop rotation systems can also decrease selection for herbicide resistance in weed populations (Beckie and Harker, 2017; Beckie et al , 2014).…”