Getting the most from your water

The importance of water quality has come into sharp relief over the past few years as growers have adopted a ‘no excuses’ attitude to optimising herbicide performance in a bid to better tackle problem weeds.

According to Tom Robinson, independent consultant best known to growers for his training courses on pesticide application, “there has been an awakening among growers for what water conditioners can do to promote spray quality and pesticide performance”.

“I’m seeing a growing interest in water quality and its importance to product performance. Many products need a water conditioner to optimise performance and growers are keen to understand how they can be a benefit,” says Tom Robinson.

With grass weeds in particular becoming increasingly difficult to control, farmers are looking for incremental gains wherever they may be found. Avoiding a reduction in herbicide performance due to some of the product being locked up by salts in the spray water, will result in a performance gain. However, an important part of maximising the benefit from a water conditioner, involves understanding how it works so the correct mixing procedure is followed.

For many growers water conditioning is the last piece in the jig-saw to better weed control: they’ve delayed autumn drilling and expanded the area of spring crops, worked hard to improve seedbed quality to promote residual herbicides, and considered nozzle choice and sprayer set-up.

“When you consider that, uncorrected, hard water can reduce the efficacy of certain herbicides by up to 30%, it’s easy to see where this interest is coming from,” says Rhodri Morris, commercial manager for De Sangosse.

Water is the primary carrier for applying crop protection products constituting more than 95% of the spray volume. Water quality can be affected by both hardness and pH, but the effects are quite distinct.

“Most growers know that they probably should include a water conditioner, especially with glyphosate or sulfonylureas, but few could tell you the difference between a cation complexing agent, an acidification agent or a competitive salting product,” he says.

Herein lies the issue. There are many ways to condition water, but choosing the right method largely depends on the issue to corrected (hard water or high pH) and often if the product being applied needs something more, such as a humectant to support leaf penetration or an anti-foaming agent to aid mixing.

For most of the UK however, hard water is the primary issue (see map). Reservoir and ground water nearly always have something dissolved in them, be it carbonates, bicarbonates, sulphates or nitrates. These affect the pH, taste and hardness. Glyphosate is a prime example of where performance can be impaired by hard water, says Rhodri Morris.

“Glyphosate is highly soluble which is why it mixes so well, but it is also an excellent chelating agent [where the chemical compounds react with metal ions to form a stable, water soluble complex]. When added to hard water the chelates in glyphosate bind with the cations to become locked up which makes them unavailable,” says Rhodri Morris.

With most herbicides the solution is to add a cation complexing agent such as X-Change and this is the recommended solution from Monsanto for Roundup because it also reduces the pH, contains an anti-foamer and a humectant. But there is a second option: ammonium sulphate.

“Some have promoted the addition of ammonium sulphate. It works differently to X-Change by out-competing the dissolved magnesium or calcium salts in the water to bind with the glyphosate meaning it cannot be bound to anything else. The ammonium also promotes photosynthesis which hastens the systemic activity of the herbicide,” says Rhodri Morris.

“While it’s better than nothing, ammonium sulphate does however, have its limitations. It will never out-compete all the dissolved salts – a complexing agent, such as X-Change is required for this – and it does nothing to correct pH,” he adds.

pH of the water is an entirely different issue that needs consideration, in some situations the pH of water will be too high to support full herbicide performance because drinking water regulations specify that the pH of water at the tap should be between 6.5 and 9.5. In most cases, the pH of water leaving a treatment works is between 7 and 8, but it can change as it passes through the network of reservoirs and pipes.

Even the lowest permissible pH of 6.5, tap water is still too high for most post-emergence herbicides which are classified as weak acids so work best at a pH of between 3 and 6.

“Above pH 7 certain pesticides can be affected by a process known as alkaline hydrolysis, this renders them permanently inactive,” says Rhodri Morris.

“It’s a gradual process and the severity depends on several influencing factors in addition to pH, including water temperature, the amount of time elapsed after mixing and the susceptibility of the pesticide to be applied. Carbamates, such as phenmedipham, and some pyrethroids, such as cypermethrin, are particularly susceptible,” he says.

“Dimethoate, an insecticide for controlling aphids in cereals and ornamentals for example, if mixed with alkaline substances (pH 9+) has a half-life of about 45 minutes. To address this issue alone, an acidifier such as Spraymac, should be considered, but this will only correct the pH of the water, while a cation complexing product, such as X-Change, will correct hard water and pH.

Mixing sequence
Conditioning the water before adding the herbicide, pesticide or insecticide however, is vital. Since the effects of hard water or high pH cannot be undone, if the appropriate mixing sequence is not followed then there is little point spending money on a water conditioner, says Tom Robinson.

The best solution, and a viable option for farms frequently using cation complexing water conditioners, is to install an inline dosing pump to pre-treat the water entering the sprayer’s water supply tank, suggests Tom Robinson.

However, in most situations, where pre-treating the water is not an option, the key to optimising the effectiveness of the water conditioner is in the mixing sequence.

“Adding the ammonium sulphate to more than a quarter tank full of water, leaves it with too much competition for it all to be effective. As a competing agent, it will never be entirely effective because it can’t outcompete all the salts,” he says.

“In contrast, a cation complexer isolates the dissolved salts so they never come into contact meaning almost all the herbicide active ingredient is available.”

To promote understanding of the effects hard water and high pH can have on pesticide performance, De Sangosse has launched ‘H₂knOw’, an initiative that seeks to help growers and agronomists to identify the specific issue and address them correctly.

“Water conditioning is not about promoting reduced rates of use: in some cases, certain sulfonylureas for example, there is only a single rate of use and no one would suggest reducing it. Rather, water conditioning is about promoting maximum efficacy,” says Rhodri Morris.

Criteria affecting product performance through water hardness

• Rate of product used, i.e. 1 litre/ha versus 6 litres/ha. • Degree of water hardness. Ask you agronomy provider for a De Sangosse water testing kit for accurate diagnosis.• Applied water rate per hectare.

Points to consider before conditioning water
• Have you followed the correct process for testing both water hardness and pH?
• How will the result affect pesticide performance if not addressed correctly?
• What is the difference between water conditioners and salt competing agents, which is most suitable for the problem identified/product being applied?
• Are you following the correct mixing sequence for the water conditioner being used?