Article taken from the CPM, written by Tom Allen-Stevens
When it comes to pesticides in drinking water, you could argue the finger of blame is somewhat unfairly pointed at farmers. Even where best practice is diligently followed, it can be the vagaries of the weather or simply where you farm that determines whether a pesticide is washed off your field and into the nearest reservoir.
That’s not how the regulators see it however, points out Rob Gladwin of BASF. “The Water Framework Directive (WFD) brings a new imperative to ensure maximum levels of herbicides in surface and groundwater are not exceeded, and there’s a timeframe to ensure compliance. WFD and pesticides regulation are now linked, so if UK water bodies don’t comply with WFD, the herbicides responsible may face revocation.”
Increasing concerns
Defra has increasing concerns about oilseed rape herbicides in particular, he points out, and plans to consult later this year on various options to reduce exceedences. “Defra’s asked the Crop Protection Association to propose a new industry-led project on Oilseed Rape Herbicide Water Stewardship. When it comes to metazachlor (MTZ), we believe the self-stewardship approach is far more effective than a label restriction, so have decided to get ahead of the curve.”
BASF is working with MAUK to develop additional measures – guidelines for a stewardship approach to MTZ that will not only bring a clear reduction in exceedences, but are practical for farmers to adopt and are based around best practice agronomy, so if followed should result in improved crop performance.
Self-stewardship is still the preferred approach, points out Paul Fogg of MAUK, but it’s got to work. “Defra is still willing voluntary measures to be the solution. WFD timelines were to achieve “Good Status” by 2015 – the end of the first round of River Basin Management Plans (RBMP). Defra;s looking for measures in the second round of RBMP (2015-2021) to deliver, if not by voluntary means then regulatory.”
MTZ gets into drinking water through two routes: point-source contamination occurs through losses from a recognised source, such as spillages, leaks or foil seals, washing the pesticide into drains in the farmyard. “This is easy to avoid – it’s a question of knowing where your drains are and adhering to good practice when filling and cleaning,” he points out.
In the field, there’s diffuse pollution through spray drift, surface run-off and pesticide moving down into field drains. “MTX binds to material in the soil, such as soil particles and organic matter. But it has a very low absorption coefficient – 50mg/l, compared with pendimethalin that has a coefficient of 5000mg/l. Even metaldehyde is better at 100mg/l, while propyzamide’s coefficient is 840mg/l. If you can keep MTZ where you want it, it’ll do the job, but it’s easy to lose it down the drain.”
Point-source contamination
When it comes to addressing the issues, Rob Gladwin notes that the advice is already available for the most part. “The Voluntary Initiative has identified point-source contamination areas for the farmyard and drawn up action plans for growers to follow. In the field, this is more of a challenge, but there are elements that can be readily addressed.
Vegetative buffer zones at the edges of fields next to water courses address the issues of drift and run-off to a large extent. “Again, there’s good advice on the VI website. The area that perhaps needs more thought is the field itself, and in particular what lies beneath it.”
MTZ applied to a good seedbed and soil structure will stay where it is and do its job, he says. “The problem lies with poor seedbeds and cracked soils, particularly on heavier land. Where there are field drains land or mole-drained, these are higher risk situations.”
There are particular UK river catchments where drinking water abstractions are most at risk. Growers themselves may not be aware that they’re in one of these areas, notes Jo Kennedy of the Environment Agency. But the EA knows exactly where they are, and has made this information freely available through its What’s In Your Bank Yard (WIYBY) web-based service. (Go to www.environment-agency.gov.uk/wiyby and click on ‘go straight to maps’, then on the tap icon called ‘Drinking Water Safeguard Zones’).
“It’s an interactive map where you type in your postcode, and it’ll tell you whether you’re in a Safeguard Zone. These are areas where drinking water abstractions are at risk because of pollutants in the river or groundwater. Water companies are already having to spend extra money on treatment or are concerned extra treatment will be needed,” she explains.
Clicking on a Safeguard Zone brings up an information box showing which pollutants are a problem in that catchment. In many of these areas, abstracted drinking water has been found to have levels of agricultural pesticides above the legal limit of one part per billion. There are 112 Safeguard Zones in England, covering just under 18,000km², and in 39 of these, OSR herbicides have been found. MTZ is causing a problem in 8 Safeguard Zones, says Jo Kennedy.
Safeguard Zones
“That’s an area of 6200km², with most Safeguard Zones for MTZ covering parts of the wider River Severn and Thames catchments. We’d encourage farmers in these areas to be especially aware of the range of industry best practice measures that can be taken to reduce risk of MTZ reaching water, and implement these so we can reduce the exceedences and the levels of treatment that are currently needed.”
Links from the WIYBY website direct to the VI website should make it easier for growers to find the information they need, she says. “But I question whether the existing VI measures will get us far enough, particularly in catchments with higher and more frequent peaks of MTZ. In more vulnerable areas in particular, we’re asking the industry to identify what extra measures can be taken – we’d like to limit the use of tougher measures where possible, to locations where they are most needed.
“But those not in a Safeguard Zone impacted by MTZ must act as well and ensure they minimise the risk of the herbicide entering water courses. The quality of water bodies that aren’t at risk is also monitored, and if this deteriorates, it will hasten the need to consider regulatory protection measures.”
This puts the spotlight quite clearly on farmers, and improvements to soil structure as the area where “additional measures” are most likely to bring results. But that shouldn’t be seen as an unrewarded obligation, reckons independent soil consultant Philip Wright.
“It’s a win-win – a soil structure that holds on to MTZ is one that’ll result in a good, well established OSR crop. The action you take at harvest and immediately afterwards is critical to how you achieve both aims.”
Growers, particularly on heavy soil, will be looking for a reasonably find crumb on the surface, with a fissured structure below. “Ideally, you should have a lot of little cracks that close up at the first sign of moisture. Large cracks, particularly in tramlines, are danger signs – they’re compacted areas that need attention.”
Similarly, any area of low organic matter, where soils have slumped or evidence of run-off are warning signs that must be address, he says. “Immediately after harvest is the ideal time for restructuring work, and the OSR crop is one that’ll really benefit if you do it right.”
Most OSR is min-tilled or direct-drilled, he continues. “So the last thing you want to do is make the surface rough. When subsoiling, you’re aiming to lift the soil without disturbing the surface. At the correct depth, with the right subsoiler leg, the soil goes into slight compression as it passes over the wing, then tension off the back – that’s when you get the beneficial fissures. Go too shallow or too fast, especially with high rake-angled components, and you boil the surface. But subsoil to deep or when it’s not dry enough and you create a new compacted zone.”
This makes the spade a key tool for checking progress, he notes. Then afterwards, consolidation is key. “Whether that’s a press or rolls, you’re looking to close up the cracks and crush the clods. This provides the sideways action – think of your soil as a jigsaw that you’re kneading back into place. It also gives you the seed-to-soil contact essential for good OSR establishment.”
Unnecessary cultivations should be avoided, he stresses – less always delivers more and controlled traffic farming or direct-drilled systems often result in the best soil structure. “But don’t ignore areas that have been badly trafficked or worked when wet, particularly when moving over to direct drilling – a little bit of remediation is not a bad thing. While drainage is a potential pathway, it’s also key to allowing timely operations when soil is at the correct moisture. This helps porosity and the ability of the soil to hold on to the herbicide.”
Strip-tilled and sub-cast OSR need to be managed with particular care, adds Philip Wright. “You can end up with a worse soil structure and large fissures – speed is often the culprit. Make sure the seedbed is well consolidated after the drill.”
A good crumb structure in the seeding zone helps both crop establishment and herbicide efficacy, agrees Clare Tucker of BASF.
“The mixture of pore sizes within and between the crumbs means good retention of both air and water,” she explains. Once applied, the herbicide is adsorbed onto soil particles but is slowly released and diffuses evenly in the soil water within the crumb structure to make good contact with germinating weeds. It lasts for about 6-8 weeks, she says – long enough to do its job early in the season, but it doesn’t hang around to be a problem.
Broadleaf weeds
“MTZ brings more than 85% control of broadleaf weeds, such as chickweed, speedwell, mayweed, groundsel, shepherd’s purse and also meadow grass. There’s an effect on blackgrass – around 70% control, depending on moisture availability and the quality of the seedbed. Quinmerac adds control of cleavers and poppies. Dimethenamid-p (DMTA-P) has the same wide weed range as MTZ plus extra activity against cranesbill, shepherd’s purse, poppy and cleaver.”
While MTZ is taken up through the root, DMTA-P is taken up by both the shoot and root of the weed. “This is important in dry conditions as it’ less reliant on rain to move the herbicide down to the rooting zone,” she notes.
“You always get the best control if the herbicide is applied pre-emergence of the weed. It will also work at cotyledon stage, and that’s useful where you have to apply a pyrethroid for cabbage stem flea beetle. But the 1-2 leaf stage is too late.
“If pre-em applications are planned, make sure your OSR is drilled to at least 15mm depth to keep it out of reach of the MTZ, and don’t spray if heavy rain is forecast within 48 hours – the herbicide needs time to bind to soil particles. We’re also recommending growers on drained land don’t use MTZ after the end of Sept.”
Chris Martin of Agrovista reckons there are three areas to focus on: “Get the crop in early, get the seedbed right, and do what you can to get the MTZ application right, too.”
OSR should really be established in Aug, he says. “Leaving it until Sept can be a disaster, and delaying establishment for blackgrass can also be a big mistake – if you have bad blackgrass, consider a winter cover followed by a spring crop.”
Cultivations should be kept shallow and consolidation is key, he advises. “We recommend double-rolling, crossing at a 30-45° angle on the second pass. Results from our Growcrop Gold trials show this brings better seed-to-soil contact, particularly for those on a one-pass system.”
Spray operators should focus on spray quality and selecting the correct fan angle to ensure a good, even coverage while minimising drift. “We’ve had good results in trials from adding Grounded or Remix to the pre-em. These are adjuvants that are positively charged, so help to bind the chemical to the soil colloids, which really makes a difference with MTZ. They also significantly reduce drift, ensuring the product hits the target and reducing risk of direct contamination into watercourses. Overall, we’ve found adjuvants can dramatically boost efficacy of some residuals.”
But while these steps will help in the field, he urges spray operators not to lapse on the VI fundamentals. “Poor farmyard hygiene is still the biggest cause of pesticide exceedences. While it’s important growers improve practice in the field, just one spill or discarded foil can undo all the progress.”
When it comes to pesticides in drinking water, you could argue the finger of blame is somewhat unfairly pointed at farmers. Even where best practice is diligently followed, it can be the vagaries of the weather or simply where you farm that determines whether a pesticide is washed off your field and into the nearest reservoir.
That’s not how the regulators see it however, points out Rob Gladwin of BASF. “The Water Framework Directive (WFD) brings a new imperative to ensure maximum levels of herbicides in surface and groundwater are not exceeded, and there’s a timeframe to ensure compliance. WFD and pesticides regulation are now linked, so if UK water bodies don’t comply with WFD, the herbicides responsible may face revocation.”
Increasing concerns
Defra has increasing concerns about oilseed rape herbicides in particular, he points out, and plans to consult later this year on various options to reduce exceedences. “Defra’s asked the Crop Protection Association to propose a new industry-led project on Oilseed Rape Herbicide Water Stewardship. When it comes to metazachlor (MTZ), we believe the self-stewardship approach is far more effective than a label restriction, so have decided to get ahead of the curve.”
BASF is working with MAUK to develop additional measures – guidelines for a stewardship approach to MTZ that will not only bring a clear reduction in exceedences, but are practical for farmers to adopt and are based around best practice agronomy, so if followed should result in improved crop performance.
Self-stewardship is still the preferred approach, points out Paul Fogg of MAUK, but it’s got to work. “Defra is still willing voluntary measures to be the solution. WFD timelines were to achieve “Good Status” by 2015 – the end of the first round of River Basin Management Plans (RBMP). Defra;s looking for measures in the second round of RBMP (2015-2021) to deliver, if not by voluntary means then regulatory.”
MTZ gets into drinking water through two routes: point-source contamination occurs through losses from a recognised source, such as spillages, leaks or foil seals, washing the pesticide into drains in the farmyard. “This is easy to avoid – it’s a question of knowing where your drains are and adhering to good practice when filling and cleaning,” he points out.
In the field, there’s diffuse pollution through spray drift, surface run-off and pesticide moving down into field drains. “MTX binds to material in the soil, such as soil particles and organic matter. But it has a very low absorption coefficient – 50mg/l, compared with pendimethalin that has a coefficient of 5000mg/l. Even metaldehyde is better at 100mg/l, while propyzamide’s coefficient is 840mg/l. If you can keep MTZ where you want it, it’ll do the job, but it’s easy to lose it down the drain.”
Point-source contamination
When it comes to addressing the issues, Rob Gladwin notes that the advice is already available for the most part. “The Voluntary Initiative has identified point-source contamination areas for the farmyard and drawn up action plans for growers to follow. In the field, this is more of a challenge, but there are elements that can be readily addressed.
Vegetative buffer zones at the edges of fields next to water courses address the issues of drift and run-off to a large extent. “Again, there’s good advice on the VI website. The area that perhaps needs more thought is the field itself, and in particular what lies beneath it.”
MTZ applied to a good seedbed and soil structure will stay where it is and do its job, he says. “The problem lies with poor seedbeds and cracked soils, particularly on heavier land. Where there are field drains land or mole-drained, these are higher risk situations.”
There are particular UK river catchments where drinking water abstractions are most at risk. Growers themselves may not be aware that they’re in one of these areas, notes Jo Kennedy of the Environment Agency. But the EA knows exactly where they are, and has made this information freely available through its What’s In Your Bank Yard (WIYBY) web-based service. (Go to www.environment-agency.gov.uk/wiyby and click on ‘go straight to maps’, then on the tap icon called ‘Drinking Water Safeguard Zones’).
“It’s an interactive map where you type in your postcode, and it’ll tell you whether you’re in a Safeguard Zone. These are areas where drinking water abstractions are at risk because of pollutants in the river or groundwater. Water companies are already having to spend extra money on treatment or are concerned extra treatment will be needed,” she explains.
Clicking on a Safeguard Zone brings up an information box showing which pollutants are a problem in that catchment. In many of these areas, abstracted drinking water has been found to have levels of agricultural pesticides above the legal limit of one part per billion. There are 112 Safeguard Zones in England, covering just under 18,000km², and in 39 of these, OSR herbicides have been found. MTZ is causing a problem in 8 Safeguard Zones, says Jo Kennedy.
Safeguard Zones
“That’s an area of 6200km², with most Safeguard Zones for MTZ covering parts of the wider River Severn and Thames catchments. We’d encourage farmers in these areas to be especially aware of the range of industry best practice measures that can be taken to reduce risk of MTZ reaching water, and implement these so we can reduce the exceedences and the levels of treatment that are currently needed.”
Links from the WIYBY website direct to the VI website should make it easier for growers to find the information they need, she says. “But I question whether the existing VI measures will get us far enough, particularly in catchments with higher and more frequent peaks of MTZ. In more vulnerable areas in particular, we’re asking the industry to identify what extra measures can be taken – we’d like to limit the use of tougher measures where possible, to locations where they are most needed.
“But those not in a Safeguard Zone impacted by MTZ must act as well and ensure they minimise the risk of the herbicide entering water courses. The quality of water bodies that aren’t at risk is also monitored, and if this deteriorates, it will hasten the need to consider regulatory protection measures.”
This puts the spotlight quite clearly on farmers, and improvements to soil structure as the area where “additional measures” are most likely to bring results. But that shouldn’t be seen as an unrewarded obligation, reckons independent soil consultant Philip Wright.
“It’s a win-win – a soil structure that holds on to MTZ is one that’ll result in a good, well established OSR crop. The action you take at harvest and immediately afterwards is critical to how you achieve both aims.”
Growers, particularly on heavy soil, will be looking for a reasonably find crumb on the surface, with a fissured structure below. “Ideally, you should have a lot of little cracks that close up at the first sign of moisture. Large cracks, particularly in tramlines, are danger signs – they’re compacted areas that need attention.”
Similarly, any area of low organic matter, where soils have slumped or evidence of run-off are warning signs that must be address, he says. “Immediately after harvest is the ideal time for restructuring work, and the OSR crop is one that’ll really benefit if you do it right.”
Most OSR is min-tilled or direct-drilled, he continues. “So the last thing you want to do is make the surface rough. When subsoiling, you’re aiming to lift the soil without disturbing the surface. At the correct depth, with the right subsoiler leg, the soil goes into slight compression as it passes over the wing, then tension off the back – that’s when you get the beneficial fissures. Go too shallow or too fast, especially with high rake-angled components, and you boil the surface. But subsoil to deep or when it’s not dry enough and you create a new compacted zone.”
This makes the spade a key tool for checking progress, he notes. Then afterwards, consolidation is key. “Whether that’s a press or rolls, you’re looking to close up the cracks and crush the clods. This provides the sideways action – think of your soil as a jigsaw that you’re kneading back into place. It also gives you the seed-to-soil contact essential for good OSR establishment.”
Unnecessary cultivations should be avoided, he stresses – less always delivers more and controlled traffic farming or direct-drilled systems often result in the best soil structure. “But don’t ignore areas that have been badly trafficked or worked when wet, particularly when moving over to direct drilling – a little bit of remediation is not a bad thing. While drainage is a potential pathway, it’s also key to allowing timely operations when soil is at the correct moisture. This helps porosity and the ability of the soil to hold on to the herbicide.”
Strip-tilled and sub-cast OSR need to be managed with particular care, adds Philip Wright. “You can end up with a worse soil structure and large fissures – speed is often the culprit. Make sure the seedbed is well consolidated after the drill.”
A good crumb structure in the seeding zone helps both crop establishment and herbicide efficacy, agrees Clare Tucker of BASF.
“The mixture of pore sizes within and between the crumbs means good retention of both air and water,” she explains. Once applied, the herbicide is adsorbed onto soil particles but is slowly released and diffuses evenly in the soil water within the crumb structure to make good contact with germinating weeds. It lasts for about 6-8 weeks, she says – long enough to do its job early in the season, but it doesn’t hang around to be a problem.
Broadleaf weeds
“MTZ brings more than 85% control of broadleaf weeds, such as chickweed, speedwell, mayweed, groundsel, shepherd’s purse and also meadow grass. There’s an effect on blackgrass – around 70% control, depending on moisture availability and the quality of the seedbed. Quinmerac adds control of cleavers and poppies. Dimethenamid-p (DMTA-P) has the same wide weed range as MTZ plus extra activity against cranesbill, shepherd’s purse, poppy and cleaver.”
While MTZ is taken up through the root, DMTA-P is taken up by both the shoot and root of the weed. “This is important in dry conditions as it’ less reliant on rain to move the herbicide down to the rooting zone,” she notes.
“You always get the best control if the herbicide is applied pre-emergence of the weed. It will also work at cotyledon stage, and that’s useful where you have to apply a pyrethroid for cabbage stem flea beetle. But the 1-2 leaf stage is too late.
“If pre-em applications are planned, make sure your OSR is drilled to at least 15mm depth to keep it out of reach of the MTZ, and don’t spray if heavy rain is forecast within 48 hours – the herbicide needs time to bind to soil particles. We’re also recommending growers on drained land don’t use MTZ after the end of Sept.”
Chris Martin of Agrovista reckons there are three areas to focus on: “Get the crop in early, get the seedbed right, and do what you can to get the MTZ application right, too.”
OSR should really be established in Aug, he says. “Leaving it until Sept can be a disaster, and delaying establishment for blackgrass can also be a big mistake – if you have bad blackgrass, consider a winter cover followed by a spring crop.”
Cultivations should be kept shallow and consolidation is key, he advises. “We recommend double-rolling, crossing at a 30-45° angle on the second pass. Results from our Growcrop Gold trials show this brings better seed-to-soil contact, particularly for those on a one-pass system.”
Spray operators should focus on spray quality and selecting the correct fan angle to ensure a good, even coverage while minimising drift. “We’ve had good results in trials from adding Grounded or Remix to the pre-em. These are adjuvants that are positively charged, so help to bind the chemical to the soil colloids, which really makes a difference with MTZ. They also significantly reduce drift, ensuring the product hits the target and reducing risk of direct contamination into watercourses. Overall, we’ve found adjuvants can dramatically boost efficacy of some residuals.”
But while these steps will help in the field, he urges spray operators not to lapse on the VI fundamentals. “Poor farmyard hygiene is still the biggest cause of pesticide exceedences. While it’s important growers improve practice in the field, just one spill or discarded foil can undo all the progress.”