A new online hub dedicated to overcoming water quality issues associated with glyphosate performance, plus the importance of its overall stewardship, has been launched. CPM investigates why adhering to best practice matters in ensuring this critical tool has a future.
“It’s not just cations, it’s water quality full stop which is critical for the glyphosate’s efficacy.” JOHN CUSSANS
By Janine Adamson
Glyphosate is arguably the lynchpin of the weed control toolbox, whether that’s in agricultural settings or beyond. However, following confirmed incidences of UK glyphosate-resistant Italian ryegrass earlier this year, experts are stressing the importance of adhering to stewardship as growers prepare for the upcoming season.
According to Bayer’s Roger Bradbury, this is compounded further by the fact glyphosate is a unique mode of action in terms of Herbicide Resistance Action Committee (HRAC) classification, therefore it must be protected.
“It’s also unique in that it’s been around for 50 years, continues to be highly effective and a vital non-selective herbicide with wide-ranging uses.”
He adds that herbicide resistance issues mostly arise from mis-use or over-use of an active ingredient, so are intrinsically linked to actions made on-farm. “However at the moment, bar the odd case, glyphosate performs and continues to be an important component of any integrated weed management programme.
ONGOING RISK
“What the glyphosate-resistant Italian ryegrass has taught us, is that we have to shine a spotlight back on stewardship and responsible use. Although the fundamentals are nothing new – as issued by WRAG (the UK’s Weed Resistance Action Group) around 10 years ago – the on-going risk must be recognised,” he urges.
This risk is heightened in situations where mechanical weeding is significantly reduced or no longer taking place, highlights ADAS’ John Cussans. “Equally, long periods of stubble allow weeds to become very large and well-tillered. In those scenarios, not only is glyphosate relied upon heavily, but it’s being asked to do a much tougher job,” he explains.
John agrees that the current situation with Italian ryegrass should be impetus for growers to pay attention to what’s going on across their own farms. “Resistance through selection is a process that happens over time; you won’t wake up one morning to find glyphosate no longer works.
“It’s a slow shift and it’s at this point when there’s still an opportunity to head the problem off. By monitoring closely and recognising patterns – noting any increases in unsatisfactory control – this helps to identify whether crop management decisions are increasing or decreasing risk. Then appropriate action can he taken while there’s a window to act.”
Although there are many factors involved in effective glyphosate stewardship, John says one aspect that makes the active ingredient particularly vulnerable, is its relationship with water.
“This is because glyphosate, a polar herbicide, has the potential to bind to the cations (calcium, magnesium and iron ions) found in water, known as lock-up. Once bound, it’s no longer active and can’t be absorbed by the target weed – this is irreversible.
“Compared with other risky plant protection products, it’s particularly susceptible due to its chemistry and volume of use,” he explains.
Hard water in particular contains high levels of cations, expressed as either degree of hardness, or as parts per million of calcium carbonate, adds John. “This is what gives a measure of concentration.
“The more water versus glyphosate in the tank, the higher the risk – meaning sub-optimum dose rates and high water volumes pose a greater chance of lock-up.”
Conventional mains water has a hardness in the range of 100-400ppm. In calcareous areas, bore holes and wells may contain up to 1000ppm, as well as iron from sandstone, or high organic matter/acid levels from springs, bogs and moors.
“Glyphosate is also affected by organic matter contamination or residues, which could be the result of capturing rainwater off a mossy roof, for example, or abstracting from bore holes. So it’s not just cations, it’s water quality full stop which is critical for the product’s efficacy,” states John.
De Sangosse’s Rob Suckling points out that in essence, poor water means poor weed kill. “Furthermore, many growers don’t know their water quality, especially hardness. Having conducted research into this area, we’ve been surprised at how much of an overlooked blind-spot it is in regard to application planning.”
This research involved speaking to more than 120 farmers, revealing that of those, just 4% knew the hardness of their water. Most were suspicious of hard water due to observing limescale in a kettle, but weren’t proactively testing, adds Rob. “While the knowledge gap around water quality was surprising, the positive news is that farmers are highly engaged with the issue.
“To help address this gap in understanding, we’ve launched our new ‘Clean Water. Clean Kill’ glyphosate stewardship campaign to highlight the importance of water quality and its role in resistance prevention.”
Having explored water hardness for some time, he shares that De Sangosse estimates that 70% of UK farms are using moderately hard to very hard water. Given that even 150ppm calcium carbonate can mean a level of lost performance, this suggests a profound potential impact on glyphosate chemistry, says Rob.
“Hard water can easily reduce efficacy by 20-30% if left unaddressed. What’s important is to differentiate this from pH, which affects the stability and uptake of some herbicides.
“Glyphosate itself is an acidifier – it acts as a buffering agent and resists pH fluctuations in the spray tank. The ideal pH for glyphosate performance is between 4 and 5, so while glyphosate likes acidic conditions, pH is not the culprit in poor control.”
To rectify the impact of hard water on glyphosate, a true water conditioner can be added to the tank, proposes John. “Unlike pH buffering, this acts as a sacrificial chelating agent, meaning the cations bind to the water conditioner before the glyphosate is added to the spray tank. This difference is why understanding what goes into the tank with any plant protection product, and its function, is key.”
In agreement, Rob explains that true water conditioners, like X-Change from De Sangosse, are designed to neutralise the minerals in hard water that deactivate glyphosate. “Therefore they protect glyphosate availability in the tank for maximum uptake.
CORRECT DOSE RATE
“But, you have to know the hardness of your spray water to dose the correct amount of water conditioner, and critically, the water conditioner must enter the tank first. In dosing correctly, the result is more active glyphosate molecules available to reach the leaf which increases kill rates.”
He adds that all water destined for a sprayer should be tested for hardness, whether that’s from rainwater, mains or boreholes. “The advice is, test don’t guess; you can’t tell whether water is hard or soft just by looking at it.
“That’s why we distributed free TDS (Total Dissolved Solids) meters at our summer open days, to help farmers assess whether they’re at risk of reduced glyphosate performance.”
The meters give a reading for TDS in ppm to quantify dissolved calcium, magnesium, and iron; the ideal hardness is <100ppm. Above 150ppm is the danger zone where a true water conditioner like X-Change will be beneficial, he suggests.
Rob hopes that by encouraging further discussion about water hardness, understanding will also improve regarding the difference between water conditioners and adjuvants. “They aren’t the same thing. A water conditioner protects the glyphosate in the tank whereas an adjuvant optimises its performance on the plant.
“With the removal of tallow amine surfactants, many basic glyphosate formulations lack the power to penetrate leaf cuticles, especially under stress conditions. An adjuvant such as Validate – which will also condition the water – should be considered when using cheaper formulations of glyphosate.”
Because so many external factors are beyond the control of growers, this is why something as simple as using the correct water conditioner at the correct rate, is vital, suggests John. “It’s the same message for all aspects of glyphosate stewardship, with water volume and quality being just one piece of the jigsaw.”
his article was taken from the latest issue of CPM. Read the article in full here.
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