Two suppliers of key oilseed rape herbicide metazachlor have joined forces in an attempt to cut incidences of its detection in surface sources for drinking water, aiming to protect the active ingredient’s availability for the long term in the process.
With the presence of pesticides in raw water threatening the UK’s ability to meet the requirements of the Water Framework Directive, Adama and BASF, who respectively make the metazachlor-based products Sultan and Butisan, have revised and reinforced their autumn recommendations and label rate under the ‘Metazachlor Matters’ advice and awareness campaign.
“This centres on a set of guidelines which reiterate the importance of following the Voluntary Initiative advice, with some specific advice,” said BASF’s Rob Gladwin.
“For this season, product reformulations also mean both companies’ products have recommended full doses of 750g/ha of active ingredient.”
The UK Metazachlor Matters campaign forms part of a wider European Metazachlor Stewardship Initiative, explained Adama’s Paul Fogg.
“Metazachlor can get into surface water via two main sources. The first, when filling or washing the sprayer, can be significant, but good operator practice can minimise this, and a lot of progress has been made in this area. The second, from the sprayed fields themselves, via surface run-off or field drainage, is a greater challenge.
“Growers should aim to establish the crop early, ideally by the first week of September, and also apply metazachlor early, something that’s particularly important on drained soils where movement risk increases with autumn rain likelihood.”
Where field drains aren’t present, there are no application timing restrictions, but for permanently or temporarily-drained fields OSR growers should aim for October 1, with an October 15 cut-off. Metazachlor can be applied after October 1 if soil/seedbed conditions are good and drains aren’t flowing.
For farmers with drained fields in Drinking Water Safeguard Zones, the cut-off is two weeks earlier, on October 1. Those unsure of whether their fields lie within these higher risk areas can visit www.wiyby.co.uk, the Environment Agency’s ‘What’s in your Backyard’ website, for guidance.
Hutchinson’s David Ellerton believes most farmers have now cracked the point source pollution problem, and are doing most things right at the right time when filling and washing down, driven by greater awareness of the risks and the ease with which they can be minimised.
He said: “Most operators are now following guidelines as a matter of course. They’re not filling the sprayer near water, are using bunded areas to fill the machine, are not leaving containers lying around, are disposing of foil tops properly and are washing the sprayer thoroughly away from the yard.
“Pollution in the field, from field drains or surface run off, is a bigger concern. The risk of drift means adequate buffer zones or a grass buffer strip should be included as a barrier adjacent to any water source. Buffer zones are vital on sloped fields – think carefully before growing oilseed rape at all on such land, as the potential risk of herbicide contamination is very high with water flow down the slope.”
If the soil is dry and cracked, metazachlor and other herbicides will go straight through the profile, and so a firm and fine consistency is essential for chemical efficacy as well as for avoiding pollution, pointed out Dr Ellerton.
“Conversely, if field drains or ditches are flowing or soils are wet, or heavy rain is expected, then avoid spraying metazachlor. The soil needs to be moist, but no more.”
He echoed Rob Gladwin’s early drilling advice, pointing out that drilling in the last two weeks of August allows time for the crop to get better established, and means the metazachlor can be applied well within the advisory window of application before the end of September, with good levels of control as a result.
“It also helps the crop withstand early season pest pressure, such as that from flea beetle, slugs and phoma stem canker.”
He reminded OSR growers they needed to remember there are two metazachlor dose rate restrictions, one for a maximum of 750g/ha of active ingredient, and the other for a maximum 1000g/ha of active over a three year period in the same field.
“There is the option of using a coformulation that generally applies less metazachlor than the straight. Those containing dimethenamid-p are useful herbicides as they have a lower ratio of metazachlor proportionately, plus additional active ingredients. Often the dose rate of the coforms applies just 500g/ha of the active.
“Also consider another herbicide might better suit the target. AstroKerb (propyzamide + aminopyralid) could be used post-emergence for good grass and broadleaved weed control.”
Weed and pest control products used in oilseed rape provide the biggest headache for water companies when it comes to cleaning up drinking supplies, according to Jodie Rettino, catchment manager at Severn Trent Water.
“Methaldehyde is our primary issue, but concerns are growing about the autumn-applied oilseed rape herbicides. We have no effective treatment processes for metaldehyde and we struggle to remove quinmerac. At a cost, most other pesticides can effectively be removed when they are at low concentrations. However, when we have a number of pesticides at high concentrations over the autumn and winter they challenge our treatment processes.”
Cost of pesticide removal from water is around £150 per million litres, with an average site treating around 26,000 million litres/year, equating to £3,942,198 per year per site. For some products, such as metaldehyde, there is no removal process.
“We have no regulatory powers, so we cannot make farmers comply with guidelines around products which are a water-pollutant issue. Instead we work on a voluntary basis with farmers and the agricultural industry, and I think this is the best way to achieve a sustainable solution for all parties. But if we cannot show that catchment management and stewardship works, Defra could bring in restrictions for certain products. By working together we have the opportunity to stop this happening.”