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Testing Your Water Source for Spray Quality

By Rebecca Hort, AAg, Extension Agrologist Intern, Yorkton

May 2024

Where do you get your water for spraying? Is it from a well or dugout? If you are using it for spraying, it is important to know if any properties will reduce the efficacy of your herbicides. If you are uncertain if your water source is suitable to use for spraying, a water test would be beneficial. Certain components of the water can antagonize specific herbicide components and reduce efficacy. For example:

  • Group 1 herbicides like clethodim and sethoxydim are antagonized by bicarbonate content in the water.
  • Calcium (Ca), magnesium (Mg) and iron (Fe) will antagonize glyphosate.
  • Calcium, magnesium, iron and bicarbonate antagonize 2,4-D amine.
  • The activity of weak acid herbicides will be reduced by calcium in the water.

A general water test for spray quality will give an analysis for conductivity, bicarbonate, Ca, Cl, carbonate, F, Fe, Mg, Mn, NO3, pH, K, Na, SO4, total alkalinity, total hardness and Total Dissolved Solids (TDS). The components within this list that have certain guidelines for sprayer quality are conductivity, total hardness and bicarbonate concentration.

Person collecting a water sample and filling a 1-litre jug
Collecting a water sample and filling a 1-litre jug

Electrical conductivity (EC) should be less than 500 uS/cm, anything over this amount can reduce the efficacy of the herbicide. The EC value of sloughs and dugouts can range from 200 to 20,000.  If you are uncertain where your water source falls in this range, a water test may benefit your farm operation.

The hardness of water is the level of calcium and magnesium present in the water. For glyphosate use, the maximum water hardness should be 350 ppm CaCO3, for low rates of glyphosate to control annual grass weeds. Maximum water hardness for higher rates of glyphosate for perennial weed control should be less than 700 ppm CaCO3. If your water is too hard, adding ammonium sulphate (AMS) to the spray water as a tank mix with glyphosate can help remove the calcium and magnesium effects.

Bicarbonate issues are typically seen in deeper wells. Concentrations of bicarbonate should be less than 500 ppm; water samples showing more than 500 ppm have a high chance of reducing the activity on Group 1 herbicides (in the “dim” group) such as Achieve, Centurion or Poast.

Making sure you choose a source that has clean water is also important for sprayer quality. Water that contains silt or organic matter particles can impact the efficacy of several herbicides such as diquat, glyphosate, bromoxynil and paraquat.

When sending in a sample, fill a one-litre plastic container with a sample representative of your water source. Depending on the source, the composition may vary at different times or places. Several samples or a composite sample may be beneficial.

There are many labs that offer water testing services. Below are some options available to producers to have water quality analyzed.

  • A&L Labs
  • AGAT Labs
  • AgVise
  • ALS Labs
  • BDS Labs
  • Down to Earth Labs
  • Element
  • Roy Romanow Provincial Laboratory
  • SGS BioVision

For more information about water quality for spray water or help submitting a sample, contact the Agriculture Knowledge Centre at 1-866-457-2377 or visit your local regional office. Your local crops extension specialist can help you send away a water sample and interpret the analysis once you receive the results.

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