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Water quality and volume important for proper weed control

February 2020

Magda du Toit, Corporate Engagement and Communications Manager SA,
Bayer. Send an email to 

Good weed control is one of the pillars on which sustainable crop production is based on. A practise that is very popular, is to replace the last cultivation before planting aimed at weed control, with a chemical weed control application. By doing this, the soil remains undisturbed and the weed seeds are not brought up to the surface.

Water is used as the carrier in almost all crop protection applications. The quality of the water used can determine the effectiveness of the product used to protect the crop. 

The quality of water used on farms is variable and often the water obtained from some sources can cause problems. Ideally the carrier water should be clear, colourless, odourless and with a neutral pH. Factors that should be considered when selecting a water source, include:

  • Solids in the water. Water with sediments in suspension may block nozzles. Sediments normally consist of fine organic matter and clays. The active ingredient in the crop protection product can also bind to these, making the product less effective.
  • Water pH is of great importance. Some pesticides are hydrolysed under acid or alkaline conditions and if not correct in accordance with the label, can neutralise the pesticide.
  • Salts in water is of equal importance. Excessive salts in water may cause damage to the crop plant when sprayed onto the leaves and can also lead to binding of the active ingredients to these salts. 
  • ‘Hard’ water contains calcium or magnesium salts which can lead to mixing problems and reducing the stability of suspensions and emulsions.

In the preparation of the crop protection mixture, the application volume also needs to receive proper attention. Application volume refers to the total volume of mixture which is applied to an area and is expressed in litres/hectare (l/ha). The volume largely depends on the apparatus used, the crop type, the target weed and the product to be used. The idea is to achieve a volume that will give good coverage, but not create a drip-off. 

It is important to follow the instructions on the label of any product always, also when determining the volumes to be applied. The label will recommend not only the dosage rate (pesticide per hectare), but also the suggested volume.

Glyphosate, and specifically the Roundup® product range with glyphosate as the active ingredient, is one of the most popular choices for pre-plant control of weeds, as well as the over the top application in Roundup Ready® crops. 

Water quality and volume is critical for successful control of weeds with any of the Roundup® products. Glyphosate is extremely sensitive to the quality of the water used for spraying. Therefore, it is important to:

  • Use high quality, clean water without soil particles or organic matter.
  • Add a 2% ammonium sulphate in the mix before the glyphosate is added if you have hard water containing salts.
  • Make sure that the pH of the mix is between 4 and 6.5. 

Because glyphosate is non-selective, take care when doing applications. 

Roundup PowerMax® contains 540 g glyphosate/lt. Reg. No. L7769 (Act No. 36 of 1947). Roundup Turbo® contains 450 g glyphosate/lt.

Always follow the instructions on the product label. 

Publication: February 2020

Section: Pula/Imvula