Figure 2. Graduate student Sithin Mathew (on the left) and Extension Weed Scientist Debalin Sarangi (on the right) are demonstrating the research trial at the Weed Management Field Day at Rosemount Research and Outreach Center.
Summary Content
The spread of herbicide-resistant weeds is a major concern in soybean production. Enhancing early canopy development in soybeans can be a valuable cultural strategy to suppress weeds by reducing the light available for their growth. This research aimed to evaluate how row spacing, planting date, soybean variety, and herbicide programs influence canopy formation, weed suppression, and yield performance.
Two field experiments were conducted in 2023 and 2024 at the University of Minnesota’s Rosemount Research and Outreach Center. The first study evaluated how two row spacings (15-inch and 30-inch) and combinations of layered residual herbicides, such as acetochlor (Warrant®), pyroxasulfone (Zidua®), and S-metolachlor (Dual II Magnum®) tank-mixed with common postemergence herbicides like Roundup PowerMax®, Liberty®, and Cobra, influence canopy development and soybean yield. The second study examined the effect of planting date (early, mid, and late May) and soybean variety (short-bushy vs. tall-slender types) on canopy closure, weed suppression, and yield. Digital canopy imaging tools and plant volume measurements were used to assess growth, and yield data were collected at maturity.
Findings
Layered residual herbicides, particularly the encapsulated formulation of acetochlor (Warrant), reduced canopy cover by 10% compared to the treatments without residual herbicides. The same treatment also reduced the yield up to 3.1 bu/a compared to no residual herbicides. Among the foliar-applied herbicides, Cobra caused yield reduction up to 3.6 bu/a. Narrow row spacing resulted in faster canopy closure.
In the planting date trial, early planted soybeans consistently developed canopy faster and produced higher yields, compared to mid and late planting. Although bushy varieties had wider canopy widths, they did not show significant advantages in canopy cover or weed suppression compared to slender types.
These findings help Minnesota farmers optimize soybean production by highlighting trade-offs between herbicide use and canopy development. While layered residual herbicides can reduce yield slightly, practices like early planting and narrow row spacing promote faster canopy closure and higher yields, offering effective, cultural weed suppression. Adopting these strategies as part of an integrated weed management approach is especially important for managing herbicide-resistant weeds.
