Corn field.

2014-15 Rapid Ag: Crop Rotation Strategies for Management of Glyphosate-Resistant Weeds

December 6, 2014

Principal Leader

Jeffrey Gunsolus


Agronomy and Plant Genetics

Funding Awarded

2014 Fiscal Year: $55,083

2015 Fiscal Year: $55,083

The Problem

Corn and soybeans are by far the most economically important crops in Minnesota and are planted on over 15 million acres. The largest threat to profitability in these systems is loss of yield due to weed competition. Advances in biotechnology allowed the use of highly effective herbicide-resistant crops to address weed control issues while giving farmers greater management flexibility and reducing overall herbicide use. However, these crops are currently being threatened by herbicide-resistant weeds, which impact crop yields, negate the value of herbicide-resistant crops, and require specialized management strategies. 


Weeds are undoubtedly the most important chronic crop pests in Minnesota, causing significant economic loss if not adequately controlled. Glyphosate is the most widely-used herbicide in Minnesota, due primarily to the development of glyphosate-resistant corn and soybean. However, the repeated use of glyphosate has led to glyphosate-resistant weed biotypes.

In Minnesota, biotypes of glyphosate-resistant common waterhemp, common ragweed, and giant ragweed have been identified and the acreage they impact is rapidly growing. Herbicide-resistant weeds are an economic and ecological concern. Rotating herbicide chemistries is one way of dealing with the issues of glyphosate-resistant weed species. However, many of the weeds resistant to glyphosate are also resistant to other herbicide chemistries. Weeds with multiple resistances reduce the efficacy of existing and developing herbicide-resistant crop technologies, limit options for weed control, and decrease profitability. With such large economic consequences and the increasing prevalence of herbicide resistant weeds, new and integrated strategies are needed to improve the timeliness of weed control.

We propose a more durable solution to preventing and managing herbicide-resistant weeds through the strategic use of diversified cropping sequences along with alternative herbicide chemistries. The success of these strategies depends on an understanding of the optimal integration of multiple control tactics based on a sound understanding of weed biology and ecology. The approach will integrate existing crop rotations, diversification of herbicide mechanisms of action, and optimization of weed control practices using weed emergence prediction models. These field experiments will allow us to determine the appropriate sequence and combination of crops for managing glyphosate-resistant weed populations and seed banks.


  1. Determine an appropriate sequence and combination of crops for management of glyphosate- and ALS-resistant giant ragweed populations and seed banks in the soil.

  2. Compare three current models and create one new model that predicts giant ragweed emergence to determine their use in improving timeliness of tillage operations and post-emergence weed control tactics in different crops.

Jeff Gunsolus presents info on weed control at Morris.

Jeffrey Gunsolus presenting information on weed control at the West Central Research and Outreach Center at Morris.