Cover crops growing in corn field.

2022-23 Rapid Ag: Managing Herbicide-Resistant Weeds Using Cover Crops

February 19, 2021

Project Leader

Debalin Sarangi, Department of Agronomy & Plant Genetics

Team Members

  • Axel Garcia y Garcia, Department of Agronomy and Plant Genetics, Southwest Research and Outreach Center near Lamberton
  • Liz Stahl, Regional Extension Office - Worthington
  • Ryan Miller and Lisa Behnken, Regional Extension Office – Rochester
  • Gregg A. Johnson, Department of Agronomy and Plant Genetics and Southern Research and Outreach Center – Waseca
  • Ce Yang, Department of Bioproducts and Biosystems Engineering
  • William Lazarus, Department of Applied Economics

Non-Technical Summary

Cover crops can boost farm profitability and sustainability by improving soil health and moisture, cutting the costs of fertilizers and herbicides, and protecting water quality; however, the success of cover crops may vary depending on the weather and soil type. In 2019, cover crops were planted only on 3.6% of corn and soybean acres in Minnesota, reflecting their slow adoption in the upper Midwest. This research proposal will be conducted at Rochester and Lamberton, MN to evaluate the importance of cover crop seeding rate and termination timing in optimizing biomass production, weed suppression, corn and soybean yields, and profitability. Advanced technologies such as unmanned aerial vehicles (e.g., drones) for capturing aerial images are now available to farmers and crop advisers; this research will also focus on predicting cover crop biomass using such technologies.

Objectives and Goals

Studies have shown that cover crop biomass positively correlates to weed control, and thus, inversely impacts weed biomass and density. However, data on critical cover crop biomass production for weed suppression in the upper Midwest is limited, especially for Minnesota. Considering the vast interests among farmers for growing cover crops in Minnesota, our specific objectives for this research are to:

  1. Determine cereal rye (Secale cereale L.) cover crop seeding rate and termination timing for optimizing biomass production, weed suppression, crop yield, and profitability
  2. Compare cover crop-based integrated weed management strategies with standard herbicide-only programs for weed control and cost-effectiveness
  3. Evaluate the use of remote sensing technology to estimate cover crop biomass and associated weed suppression

Justification

Corn and soybean are the most economically important crops in Minnesota and were planted on over 15 million acres in 2020 (USDANASS 2020). However, a significant portion of these acres was infested with herbicide-resistant weeds, predominantly glyphosate and acetolactate synthase (ALS) inhibitor-resistant waterhemp, giant ragweed, and common ragweed. In surveys conducted across Minnesota at Private Pesticide Applicator Recertification Workshops in 2020 (n=1,007), 83% of the respondents reported they had herbicideresistant weeds on their farm (Ms. Liz Stahl, personal communication). Moreover, in 2016, waterhemp biotypes resistant to more than two herbicide sites of action were reported from several soybean fields in south-central Minnesota. It is established that if the problem of herbicide resistance is addressed only with herbicides, evolution will eventually win. Therefore, an integrated approach that includes non-chemical management approaches such as cover crops along with herbicides should be considered for sustainable management of weeds and their seedbank.

Soil residual herbicides applied preemergence at crop planting are recommended for early season weed control. However, some of these chemicals such as acetochlor, atrazine, metribuzin, and isoxaflutole, etc. have use limitations in parts of Minnesota due to concerns around ground and surface water contamination.

Cover crops terminated at or after cash crop planting can provide an alternative to preemergence herbicide treatments, but their weed suppression ability will depend on the biomass attained at termination. Cover crops are gaining importance in Minnesota for having numerous benefits, including soil health and weed control. The Agricultural Census by USDA has reported a 42% increase in cover crop acres in Minnesota in 2017 compared to 2012; however, planted acres under cover crops were only 3.6% of the cash crop (corn and soybean) acres (USDA-NASS 2019). Growers face many challenges for cover crop adoption, including a shorter growing season that can hinder cover crop establishment and biomass production, resulting in challenging economic trade-offs (Rusch et al. 2020). A lack of sufficient data addressing these challenges is a significant contributor to the slow adoption of cover crops in Minnesota compared to other corn-belt states.

Cereal rye is a cold-tolerant species that can outcompete annual and biennial weeds when attaining critical biomass in spring (Ryan et al. 2011) and can survive low winter temperatures in Minnesota and be successfully included in corn-soybean crop rotations (Feyereisen et al. 2006; Rusch et al. 2020). This cover crop can also use soil N and reduce nitrate contamination to the groundwater (Feyereisen et al. 2006). However, limited data is available on seeding rate and termination timing in Minnesota critical for biomass production to achieve sufficient weed suppression.

Recent advancements in remote sensing and spectral reflectance technologies could enable rapid estimation of cover crop growth, biomass production, and weed suppression at a larger scale by using imaging platforms such as manned or unmanned aircraft, and satellites. This technology has already been used widely in cash crop breeding and variety development research. The introduction of unmanned aerial vehicle (UAV) mounted multispectral cameras can capture high-resolution images across larger areas repeatedly. Mapping cover crops for biomass production can impact growers’ decisions on cover crop termination, cash crop planting, and weed management. Several agricultural cooperatives now have access to UAVs and imagers, and they will benefit from this proposed remote sensing work.

Our research and extension plan fits well with the goal of the Rapid Agricultural Response Fund as we are planning to conduct problem-solving research in both corn and soybean production systems, where results can be used immediately by farmers and those that advise them in the short-term to promote sustainability in Minnesota’s agriculture. We will have Sarangi’s start-up funding to initiate this research in the Spring of 2021, and we are requesting funds for two years for the completion of this work.

Short-term benefits: Generate new knowledge about cereal rye seeding rate and termination timing critical for weed suppression; provide research-based information to detail the tradeoffs of implementing various cover crop practices; use remote sensing technologies to monitor cover crop performance; and facilitate communications between the scientific community and stakeholders.

Long-term benefits: Develop integrated weed management strategies to help mitigate herbicide-resistant weed problems; enhance economic, environmental, and social sustainability; and use satellite imagery for farm-decision management.

References

  • Feyereisen GW, Wilson BN, Sands GR, Strock JS, and Porter PM (2006) Potential for a rye cover crop to reduce nitrate loss in southwestern Minnesota. Agron J 98:1416–1426
  • MacLaren C, Swanepoel P, Bennett J, Wright J, and Dehnen-Schmutz K (2019) Cover crop biomass production is more important than diversity for weed suppression. Crop Sci 59:733–748
  • Osipitan OA, Dille JA, Assefa Y, and Knezevic SZ (2018) Cover crop for early season weed suppression in crops: Systematic review and meta-analysis. Agron J 110:2211–2221
  • Rusch HL, Coulter JA, Grossman JM, Johnson GA, Porter PM, and Garcia y Garcia A (2020) Towards sustainable maize production in the U.S. upper Midwest with interseeded cover crops. PLoS ONE 15:e0231032
  • Ryan MR, Mirsky SB, Mortensen DA, Teasdale JR, Curran WS (2011) Potential synergistic effects of cereal rye biomass and soybean planting density on weed suppression. Weed Sci 59:238–246
  • [USDA-NASS] United States Department of Agriculture – National Agricultural Statistics Service (2020) Minnesota Ag News – Crop Production. Available at: https://www.nass.usda.gov/Statistics_by_State/Minnesota/Publications/Cro... 20/MN-Crop-Production-09-20.pdf.
  • [USDA-NASS] United States Department of Agriculture – National Agricultural Statistics Service (2019) Census of Agriculture. 1:51 Available at: https://www.nass.usda.gov/Publications/AgCensus/2017/Full_Report/Volume_... usv1.pdf.
  • [USDA-SARE] United States Department of Agriculture – Sustainable Agriculture Research and Education (2020) National Cover Crop Survey – Annual Report 2019-2020. Available at: https://www.sare.org/wp-content/uploads/2019-2020-National-Cover-Crop-Su....