For the past two years, Annika Rowland, a graduate student in the Sustainable Cropping Systems Lab at Cornell University, has been studying how to manage weeds in soybean production without the use of herbicides or cultivation. Rowland’s experiment mimics an organic, no-till system, which can provide several environmental benefits. Organic farming prohibits the use of synthetic herbicides, which have been linked to environmental problems and concerns about human health. Soil tillage is commonly used in organic crop production for weed management, but this practice can contribute to soil erosion and other environmental problems.
No-till planting organic crops into mulch from cover crops is a promising alternative. However, weed management can be challenging in this system without herbicides or cultivation. Therefore, Rowland tested three cultural and physical weed management tactics in organically managed soybean: 1) using a high soybean seeding rate to shade out weeds; 2) mowing weeds between crop rows with a IRM-X4 inter-row mower (R-Tech Industries, Ltd); and 3) electrocuting weeds that grow above the crop canopy with a Weed Zapper Annihilator (Old School Manufacturing, LLC).
Many little hammers
As part of a field experiment, she compared each tactic alone and in all possible combinations at Cornell Musgrave Research Farm in Aurora, NY. A foundational principle in Integrated Weed Management (IWM) is to use multiple tactics, and previous research has shown that the “many little hammers” approach, where several tactics that may not be effective when used in isolation can often provide effective weed management when they are used in combination.
Building on the concept of the “many little hammers”, Rowland hypothesized that combining a high soybean seeding rate, inter-row mowing, and weed electrocution would decrease weed biomass and increase soybean yield compared to each tactic used in isolation. The tactics targeted weeds in different areas and at different times, as the high seeding rate suppressed weeds within the crop row early in the season, the inter-row mower controlled mid-season weeds growing between crop rows, and the Weed Zapper controlled weeds growing above the soybean canopy later in the season. In both years of the experiment, inter-row mowing occurred twice when soybeans were at the V4 and V5 growth stage. Weeds were between 6 and 12 inches tall when mowing occurred and consisted mainly of common ragweed, common lambsquarters, and foxtail species. The Weed Zapper was used when soybeans were at the R2 to R3 growth stage. In Rowland’s experiment, very few weeds grew above the soybean canopy at the time of weed electrocution.
The inter-row mower alone reduced weed biomass by 60% compared to the no weed management control treatment. Adding the high soybean seeding rate and/or weed electrocution to inter-row mowing did not provide additional weed control. The Weed Zapper did not reduce weed biomass compared to the control treatment, likely because of the lack of weeds above the soybean canopy when weed electrocution occurred. However, previous research at the University of Missouri demonstrated that faster-growing species, such as giant ragweed and waterhemp, can be controlled with electrocution. Research in Missouri also demonstrated that weed electrocution can reduce weed seed viability, which can lower soil weed seed bank populations over time.
More research is needed to better understand tactic compatibility and how to optimize inter-row mowing and weed electrocution. Although this research was conducted with the context of organic crop production, these tools could also be used in conventional production and assist with the control of herbicide resistant weeds.
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