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Herbicide & Groundwater

groundwater.pngHerbicide Diversification
Using a diverse mix of herbicides is an important strategy for maintaining effective weed control in corn and soybeans. In a Roundup Ready® system, this means integrating pre-emergence herbicides, using sequential treatments and/or tank mix partners in the weed management program.

To help producers compare strategies, the University of Minnesota Applied Weed Research team evaluates corn and soybean herbicide strategies for weed control, yield and returns.  See results from the 2012 Corn and Soybean Herbicide Evaluations and 2012 Diversification Options.

Herbicide Label Restrictions or Advisories
While integrating a variety of herbicides is essential for maintaining effective weed control in the long run, many labels have application restrictions or groundwater advisories based on conditions that are common in Dakota County. University of Minnesota Extension-Dakota County, Dakota County Water Resources Department and Office of GIS collaborated to develop a web-based interactive map that quickly identifies these sensitive areas of coarse-textured soils (sands, loamy sands & sandy loams) and shallow groundwater throughout rural Dakota County where restrictions or advisories may apply. Launch the interactive map.

Herbicide Reference Tables
Herbicides evaluated in University of Minnesota corn and soybean trials that contain application restrictions or groundwater advisories are included in the reference tables. Read the label as it is the final authority.

Table 1 focuses on application restrictions where herbicides cannot be used if certain conditions exist.  Please note that restrictions based on “sand” do not apply in Dakota County, since the County doesn’t have any soils that are classified strictly as “sand.”  Groundwater advisories, however, would apply.  Application restrictions that apply in Dakota County include herbicides that contain alachlor (Micro-Tech and IntRRo) or acetochlor (Harness, Surpass, Degree, Surestart, others).

Table 2 includes herbicides that contain a groundwater advisory.  Groundwater advisories generally state that the herbicide has properties that make it susceptible to leaching, particularly on coarse-textured or permeable soils where groundwater is shallow.  Judicious use of these herbicides is strongly encouraged.

Table 3 is a summary of pre-emergence and post-emergence corn and soybean herbicides that do not reference groundwater application restrictions or advisories.

Dakota County Application Restrictions
In Dakota County, there are two herbicide active ingredients that trigger an application restriction: alachlor and acetochlor.

The alachlor (MicroTech and IntRRo) restriction states that it cannot be applied to highly permeable soils where the depth to groundwater is less than 30 feet. 

Restrictions for herbicides containing acetochlor (Harness, Surpass, others) are based on the following conditions:

  • Sands with < 3% organic matter OR
  • Loamy sands with < 2% OM OR
  • Sandy loams with < 1% OM AND
  • Depth to groundwater is < 30 feet

Many labels restrict acetochlor applications only within a certain setback range from wells when these soil and groundwater conditions exist (see Table 4).  In 2013, these setbacks vary by company, so refer to the label for final authority.

For more information on the interactive map, contact Neith Little at University of Minnesota Extension-Dakota County (651-480-7723 or

The information provided in this application is intended for educational purposes only and is not guaranteed in any way.  Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the University of Minnesota or Dakota County is implied. Information provided is not intended to replace actual local groundwater knowledge.

Soil texture classifications are derived from Soil Survey of Dakota County, 1983.

The depth to groundwater classification is based on a statistical analysis of well construction records and Department of Natural Resources observation data. It represents a 97.5% confidence level that the average water table has not been less than 30 feet deep during the period of record.

Last updated: 4/24/2014 6:29 AM