Spillage is the most likely cause of the herbicide “spike” in river water that would have led Thames Water to shut a treatment plant last week had not soil contamination already done so, say agronomists.
TAG’s Jon Bellamy, who advises farmers on 60-70% of the arable land in the Cherwell catchment, was surprised by the finding, especially as the window for propyzamide’s key use, on oilseed rape, was only just opening.
“None of my farmers has put any Kerb on yet. I’ve made only three recommendations so far, and they haven’t even ordered it.”
One possibility was that a large area elsewhere sprayed just before heavy rain had led to run-off.
“It’s either that or an accident, which you can’t legislate for.” Lack of attention might have led to a sprayer being over-filled and the spillage finding its way into a yard drain, he suggested.
Propyzamide was approved for use in forestry and during hedge-planting, he added. “It’s just possible that someone might have been using it on a new hedge right next to a ditch.”
“A lot of oilseed rape was sown late, slow to establish and weeds have also been slow coming through. There’s been very little product moved from distributors’ stores yet.
“Another use at this time of year is pre-emergence in winter beans.”
With simazine gone the key remaining herbicide options for the crop were propyzamide and carbetamide, said Mr Stormonth. “The bean market has definitely increased this year. And the rain and snow that affected the area can’t have helped.”
But Mr Bellamy dismissed the idea that bean applications could be responsible for Grimsbury’s problem. “I’ve certainly made no recommendations for Kerb on beans – I always use carbetamide, as it’s better on rougher seed-beds.”
ProCam’s David Ellerton was also concerned to learn of the Grimsbury closure.
“The last thing we need is propyzamide in water at 50 times the permitted level right at the start of the spraying season.
1 Fill in the field using a bowser system. Sites should be 10m from any surface water and soils must be “cropped” and not compacted
“We haven’t sent any Kerb out yet as we’ve been waiting for temperatures to drop. The difficulty with something like this is working out where it came from.”
Propyzamide and carbetamide were vital in controlling grassweeds resistant to other herbicides.
“If we lost them, it would make oilseed rape unviable in quite a few areas, especially where there is resistant blackgrass.”
With that key break crop gone the impact on cereal growing could be “disastrous”, warned Dr Ellerton.
Voluntary Initiative manager Patrick Goldsworthy said the propyzamide had peaked for only a short period when the river was muddy. And given no reported agricultural applications, the more likely explanation was a spill or non-crop use.
But growers must use pesticides responsibly, stressed Mr Goldsworthy.
Besides propyzamide, carbetamide and metaldehyde were also being found in raw water at unacceptable levels, he noted.
“If growers want to keep the option of oilseed rape open they must raise their game.”
Dow AgroScience’s Robin Bentley said Propyzamide was strongly adsorbed on to soil particles. “So good soil management is as important as correct product handling and application technique to keep it out of the water.”
He urged growers to follow the VI’s best practice advice.
“If weather looks unsettled, rethink the timing of propyzamide applications, as rain water run-off post application may lead to presence in watercourses, something that must be avoided.”
“Propyzamide is a valuable molecule for farmers to control all the main grassweeds in oilseed rape and beans, particularly blackgrass where there are no instances of resistance,” said Mr Bentley.
“Used as recommended, Kerb Flo will continue to be a viable control option.”
All necessary steps to protect water must be adopted, urged the VI’s Patrick Goldsworthy. These included:
• Make sure your filling area is up to scratch (see below)
• Leave 50% surface trash and coarser seed-beds to avoid soil erosion
• Plan applications within a catchment so high risk fields, e.g. those with more than 5% slope, are treated earlier (accepting some compromise in weed control)
• Grass buffer strips should be strategically placed on slopes and next to water to filter out sediment and surface run-off
• Application timing must take full account of drain flow and the weather in the following five days
• Tramlines need to run across slopes
• For slug pellets use a 6m wider bout width on the headlands to ensure
Further Dow advice • Applications should be made when soils are moist but not waterlogged. A rough guide is 80% field capacity, but before drains are flowing. This will prevent accidental run-off.
• Kerb Flo performance is best when the crop has been established using min-till techniques and it works best when applied to a firm, clod-free seed-bed.
• Applications are best made when soil temperatures are declining. Target temperature is 10C and falling. Kerb Flo is less effective in warmer soils.
• Use a designated mixing and filling area, avoiding hard ground or concrete, unless bunded. Never fill sprayers near to watercourses and avoid spills.
• Do not overspray buffer zones and make sure spray is directed at the target. Engineer tramlines so they run across slopes where practical.
• Use an induction bowl or closed transfer system when available and check sprayers for drips and leaks, keeping an area of crop to spray out tank washings.
Further Dow advice
• Applications should be made when soils are moist but not waterlogged. A rough guide is 80% field capacity, but before drains are flowing. This will prevent accidental run-off.