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Southern Minnesota research highlights: Take control of resistance management

Lisa Behnken, Extension Educator-crops, and Phyllis Bongard, Educational Content Development and Communications Specialist

A large research team comprised of faculty from Extension, the Research and Outreach Centers at Waseca, Lamberton and Rosemount, and the University of Minnesota St. Paul campus conduct field research trials annually in southern Minnesota to address local, timely crop production issues. Highlights from the 2014 research report include a demonstration of weed control timing, herbicide resistance management, and a review of new herbicide technologies. All of the southern Minnesota reports from 2014 are available on the University of Minnesota Crops Research website.

Timing of weed control in corn and soybean

Photo 1. Roundup PowerMax applied to soybean at three different weed sizes and resulting yields (POST I, POST II AND POST III).

Proper timing of weed control is essential for maximizing profitability in corn and soybean cropping systems and for controlling weed seedbank production. Researchers established a demonstration that compared timing of several herbicide applications in both corn and soybeans: Preemergence (at planting), POST I (1-2” weeds), POST II (2-4” weeds), POST III (4-6” weeds) and several PRE/POST combinations. The demonstration clearly showed the value of robust early-season weed control. In addition to increased yields, the early-season control increased the amount of time available (window of opportunity) to make effective POST herbicide applications. In contrast, poor or no early-season weed control affected yield and greatly reduced the window of opportunity to effectively control weeds with POST herbicides. The Time of weed removal in soybean and Time of weed removal in corn articles are jam packed with photos from the demonstrations. Seeing is believing!

Resistance management

Photo 2. Jared Goplen discusses strategies for managing giant ragweed seedbanks.

Managing ALS- and glyphosate-resistant giant ragweed has become a widespread concern in Minnesota. It is difficult to control with preemergence herbicides and its large seed can emerge from deeper in the soil. However, its early emergence pattern and relatively short seed viability offers opportunities to manage the seedbank. Recent research suggests that 77 percent of the giant ragweed emerges by the end of May. By delaying soybean planting to this time, a large proportion of the giant ragweed population could be controlled, while maintaining 90 percent of the soybean yield potential. In addition, if giant ragweed is not allowed to go to seed, ninety-seven percent of the seedbank could potentially be depleted in two years. A full series of videos on this herbicide resistant giant ragweed research is available on the University of Minnesota Extension Crops YouTube channel.

New herbicide technologies

Several studies compared new chemistries to local standards in corn, soybeans and a non-crop situation. The objective of these studies was to show the efficacy, limitations, and management concerns of new weed control systems:

New herbicide technologies in non-crop plots

Engenia, a new, low-volatility version of dicamba, was compared to 2,4-D, Callisto (mesotrione) and Balance Pro (isoxaflutole) at application times from preemergence to 5-6” weeds (except Balance Pro, which was applied only as a preemergence treatment). A full series of photos document weed control from herbicide application to the end of June for several of the 14 treatments.

Corn herbicide trials

  • Evaluation of Acuron - Acuron contains a new active ingredient herbicide (bicyclopyrone) that is similar to mesotrione, but has a broader spectrum of broadleaf and grass control.
  • Giant ragweed control with DiFlexx - DiFlexx contains the diglycolamine salt of dicamba with a corn safener, cyprosulfamide (Site of action group 4).
  • Evaluation of Anthem - Anthem is a premix that contains pyroxasulfone (Zidua) and fluthiacet-ethyl (Cadet) (SOA 15 & 14).

Soybean herbicide trials

Other research topics

In addition to the research highlighted here, the 2014 summary also includes corn hybrid and soybean variety trials, nutrient management topics and the Integrated Pest Management Assessment.


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