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Water Quality and Herbicide Applications

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Water quality for herbicide applications is defined by its hardness, pH, alkalinity and turbidity.

Hardness and pH

Hard water is classified by high concentrations of positively charged atoms (cations)1. Hard water can be problematic because these cations can bind to herbicides causing a decrease in efficacy of the product2. Most research looking at herbicide antagonism with hard water has found Ca2+, Mg2+, Mn2+, Na+ and Fe3+ to be the most problematic. The pH of the water solution can also exaggerate the impact of hard water on herbicide activity.

Mineral Parts per million (ppm) in water World Health Organization water classification
0-114 Soft
114-342 Moderately Hard
342-800 Hard
>800 Extrememly Hard

Note: Some hard water test result will be in "trains", which is the ppm divided by 17. 

Most post-emergence herbicides are weak acids, meaning they have a pKa value less than 71. If the pH of the water is greater than the pKa of the herbicide, the product has a greater chance to dissociate1, thereby reducing the efficacy of the product1,3. Addition of ammonium sulfate (AMS) can reduce the interaction between hard water and herbicides, which helps the product to penetrate the plant cell membrane1.

Alkalinity

Soft water can be high in bicarbonates (HC0-) or carbonate (C02-), which can also interfere with some herbicides, similar to the hard water ions. When testing water for alkalinity, levels should be below 300 ppm1.

Turbidity

Turbid water describes a water source that has suspended particles which could include soil, organic matter, algae, salt or contamination from runoff. Herbicides have the potential to bind to these particles in the water source, ‘tying up’ the active ingredient and decreasing the efficacy of the product. An example of an active ingredient that binds tightly to organic content is Glyphosate, therefore it is very important to have clean water when applying a Glyphosate product.

What can be done?

  • Ensure water source is free from sediment – any amount of sediment can be problematic; if you visually see particles, consider a different water source.
  • Perform a water analysis to determine suitability for herbicide applications (i.e. hardness, pH, total dissolved solids, etc.).
    • Water testing can be performed by dedicated laboratories.
    • Hard water/pH testers can also be purchased from local pool stores.
  • Ideal water pH for weak acid herbicides is 5-7; if the pH is too high (over 8), consider a different water source.
  • For hard water, studies have shown AMS could be added to Picloram and Aminopyralid to mitigate hard water impacts, although there has not been a rate identified specifically for these products.
    • The recommended rates of AMS with Glyphosate are 2.5-5% v/v of a 400 g/L AMS solution.
    • If water is over 1,000 ppm and you are applying Aminopyralid or Picloram, consider adding AMS at 20.4 g/L.
  • A jar test can be performed before putting any products in the spray tank to ensure they will not create any problems.
  • Follow all label directions for tank mixes and adjuvants.
  • For best results, Corteva Agriscience™ recommends using clean fresh water sources for spray solution. Using open bodies of water or poor-quality water (sediment, hardness or high pH) as a source increases risk of having water issues.

Corteva Agriscience™ has a total portfolio of solutions to fit the professional vegetation managers’ needs. For more information about Corteva Agriscience products or to contact our Vegetation Management Experts visit us at IVM.corteva.ca

References

1Hall, Linda, Beckie, Hugh and Wolf, Thomas. 1999. How Herbicides Work: The biology of application. Alberta Agriculture and Rural Development. Information Management. 7000-113 Street, Edmonton, Alberta.

2Patton, Aaron J., Weisenberger, Daniel V. and Johnson, William G. 2016. Divalent Cations in Spray water Influence 2,4-D efficacy on Dandelion (Taraxacum officinale) and Broadleaf Plantain (Plantago major). Weed Technology 30:431-440.

3Zollinger, R.K., Nalewaja, J.D., Peterson, D.E. and Young, B.G. 2010. Effect of hard water and ammonium sulfate on weak acid herbicide activity. J Am Soc Test Mater Int 7(6):1-10.

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