Test your sprayer water

Water quality factors will reduce herbicide performance. Hard water ions, for example, tie up glyphosate molecules and make them ineffective. Ammonium sulphate added to the sprayer tank will counteract hard water cations and improve glyphosate performance.

Hard water

Calcium and magnesium are the most common cations in hard water. Sodium, potassium and iron are others. Cations have a positive charge and they bond with negatively-charged herbicide molecules, making the herbicide molecules useless for weed control. The more cations in the water, the more herbicide molecules lost.

Glyphosate is particularly sensitive to hard water. Hard water cations can also affect Group 10 glufosinate and certain Group 1, Group 2, Group 4 and Group 27 herbicides.

Calcium, for example, has a plus-two charge and glyphosate has a negative-one charge. Thus, every calcium cation in hard water can bond with two glyphosate molecules. This creates a useless new molecule called calcium glyphosate.

Water with hardness over 300 ppm (parts per million) is the general threshold for action.

Hard water treatment options

Test water from a few local sources to find one with lower cations.

Use the higher label rates of herbicide. Glyphosate at the low rate of 180 grams of active ingredient per acre could see a big drop in efficacy if sprayer water has high cation content. The high rate of 360 grams per acre can provide decent control, even if cations tie up half the glyphosate molecules.

Ammonium sulphate added to water before the herbicide (this mixing order is critical) will bind with the hard water cations. It dissolves in water to form ammonium and sulphate. The negatively-charged sulphate ions bond with the cations so they can’t interact with the herbicide molecules. The positively-charged ammonium ions bond with glyphosate to create ammonium-glyphosate, an effective herbicide. Agriculture labs that test sprayer water will recommend how much ammonium sulphate to add to counteract cation content

Non-ionic surfactant for 2,4-D amine specifically, at a rate of one litre per 1,000 litres of water. Ammonium sulphate does not work to improve results for 2,4-D amine.

The following three are not as good as switching water sources or adding ammonium sulphate. (1) Lower water volumes will reduce the ratio of water cations to glyphosate molecules, but low water volume is not helpful for most herbicides – including the glyphosate tank mixes, (2) urea ammonium nitrate (UAN) supplies ammonium that can bind with glyphosate to maintain performance, but it doesn’t contain the sulphate that bonds with the cations, and (3) acidifiers lower water pH and neutralize the herbicide charge, making them less likely to bond with cations, but some herbicides fall out of solution at low pH and plug the sprayer.

Other water quality issues

Conductivity

A conductivity test of water indicates the total amount of salt ions in solution, but doesn’t indicate which ions. In general, water with conductivity over 500 microSiemens per centimetre (µS/cm) could start to affect herbicide performance. Sprayers 101 says values over 1,000 need investigation to identify the ions present and what they mean to herbicide performance.

Bicarbonate

Some ground waters contain relatively high levels of bicarbonate ions, which can affect the performance of 2,4-D amine (Group 3) and some Group 1 herbicides – especially the “-dims”. The common threshold, as noted in the Sprayers 101 article, is 500 parts per million.

Dirty water

Silt and organic matter can deactivate herbicide active ingredients diquat, paraquat, glyphosate, dicamba and bromoxynil.  Dugout water, for example, can start clean in spring and get dirtier as the season progresses. This is not an issue with well water.

Labs that analyze water

Agvise Laboratories 
North Dakota 
Canadian receiving facility: 
380 Kimberly Road, Winkler, Man., R6W 0H7
Phone: 1-701-587-6010
Website: agvise.com 

A&L Canada Laboratories 
London, Ont.
Phone: 1-855-837-8347
Website: alcanada.com 

AGAT Laboratories 
Calgary, Alberta
Phone: 1-866-764-7554
Website: agatlabs.com/agri-foods-agri-analysis/ 

Agriculture labs that test sprayer water will recommend how much ammonium sulphate to add to counteract cation content. If farms already have water test results from a provincial lab, private agriculture labs can provide conditioner recommendations based on those results.

Check herbicide labels

Labels will often indicate water quality recommendations. The following four examples are verbatim from the Saskatchewan Guide to Crop Protection (2025):

Glyphosate (Group 9): “Hard water” or water containing calcium (Ca), magnesium (Mg) or iron (Fe) ions will reduce the activity of glyphosate products proportional to the level of hardness. Reducing application water volume and /or adding ammonium sulphate at 1.2 kg per acre (99 per cent dry) or 2.4 L per acre (49 per cent solution) will reduce the negative effects of low levels of hard water ions. If water is extremely hard (greater than 700 ppm or 40 grains), another water source should be found. Dirty water or water with suspended soil or organic matter will reduce control.
Clethodim (Group 1): Clethodim activity is reduced by levels of bicarbonate ions in spray water equal to or greater than 500 ppm. The addition of ammonium sulphate at 1.6 L per acre (490 g per L liquid) or 0.8 kg per acre (99 per cent dry), or the addition of 28-0-0 liquid fertilizer at 0.5 L per acre to the tank prior to the addition of clethodim has been shown to restore control.
Tralkoxydim (Group 1): If water analysis shows bicarbonate levels are 400 ppm or greater, add 0.9 to 1.8 kg of active ammonium sulphate per 100 L of spray water prior to mixing to eliminate antagonism.
Infinity (Groups 6 + 27): Ammonium sulphate at 200 g of active ingredient per acre may be added for improved broad leaf control (202 grams per acre of 99 percent dry; 0.5 L per acre of 40 percent liquid; or 0.4L per acre of 49 percent liquid).