With water companies increasingly on the lookout for oilseed rape herbicides metazachlor and quinmerac, what can growers do to help reduce their entry into watercourses and protect their availability? Marianne Curtis reports.
Concern about oilseed rape crop viability in the face of cabbage stem flea beetle and slug attacks is leading growers to delay herbicide applications, which could have consequences for water quality and future chemical use.
Input investment is under scrutiny, with growers unwilling to commit to herbicide applications until they are sure the crop has established, says BASF head of business development and sustainability Rob Gladwin.
He says: “There are more post-em applications with a slight increase in applications in October. With later applications the risk to water is increased.
“The ideal scenario is products are applied early, on to well-structured seed beds. This ensures they do their job of protecting newly-emerged seedlings from invasive weeks, while also ensuring the active is subsequently broken down and the risk of movement to water later in the season is allayed.”
Under Metazachlor Matters stewardship guidelines, recommended active dose is 750g/hectare. Where there are no drains there are no timing restrictions, while in drained fields growers should aim to apply by October 1 with a cut-off of October 15. For drained fields in Drinking Water Safeguard Zones the cut-off is October 1, says Mr Gladwin.
“Applications after October 1 can be made as long as seedbed conditions are good and drains are not flowing,” he adds.
Severn Trent Water offers an environmental protection scheme (STEPS) where growers in priority catchments are eligible for 50% grants of up to £5,000/year, says Dr Rettino. “These are available for infrastructure and in-field improvements with a clear water quality benefit.”
Applications are scored according to relevance to local water quality issues, location in a catchment and engagement with a Severn Trent Water catchment officer. Biobeds and biofilters are examples of methods which may attract funding.
In another scheme, aimed at reducing entry of metaldehyde into water destined for drinking, Severn Trent Water offers growers up to £8/ha to cover the average cost difference between ferric phosphate and metaldehyde on high risk fields in priority catchments. These are identified using remote sensing satellite imagery.
Maintaining access to metazachlor is vital, says Agrii agronomist Andrew Richards.
“Oilseed rape has become the most important break crop by far, but the problem is we have very few active ingredients available to us. For broadleaved weeds, in particular, we’re dependent on metazachlor- and quinmerac-based materials. It’s a limited armoury.”
While metazachlor remains the main oilseed rape herbicide screened by water companies, they are also increasingly looking for quinmerac.
Dr Dinah Hillier, catchment manager at Thames Water, says: “Pesticides such as quinmerac, clopyralid and metaldehyde are not as well removed by advanced water treatment.”
Dr Jodie Rettino, catchment manager at Severn Trent Water, outlines the consequences of quinmerac being recorded at twice the drinking water standard in Draycote reservoir, near Rugby, Warwickshire.
“Quinmerac was recorded at 0.208ppb. As a consequence, the water treatment works was shut down for 14 days. The reservoir holds 22,730,000cu.m of water. The total amount of quinmerac was calculated to be 4.72kg from a catchment of 72,000ha. The approximate cost of the quinmerac was £40 – the cost to the water company, in excess of £150,000.
See also: Metaldehyde-free farming trial expanded
“On average it costs £150 per megalitre [one million litres] of water to remove pesticides. An average site will treat about 26,000 megalitres of water per year which gives a total treatment cost of £3,942,198 per year.”
Heavy, under-drained soils are most likely to lead to water contamination problems, she adds.
Jim Reeve farms 530ha near Leamington Spa, Warwickshire. The farm area includes 300ha of wheat – he has a 2,100-tonne/annum contract with Warburtons – and 100ha of oilseed rape. A local vegetable producer rents 60ha for salad onion production. Soil type ranges from sandy loams to boulder clay.
As the first chairman of the Voluntary Initiative in the 1990s, Mr Reeve has long had an interest in water quality.
He recently obtained a £10,000 grant from Natural England which has gone towards a state-of-the-art £50,000 chemical store. “We can keep the sprayer under cover which stops it being rained on overnight,” he says.
Overground tanks account for 20% of the facility with a 5,600-litre underground tank. “Sprayer operation is more efficient. You are not walking around with cans. Spillage is expensive if it happens. There is a biofilter for IBCs comprising soil, compost and straw,” says Mr Reeve.
About six miles of the farm’s land adjoins a watercourse. As well as following stewardship advice relating to dosage and timing, other measures can make a significant difference, according to Mr Reeve. “Just by altering the tramlines so they go across the slope has eliminated surface flow from six to eight times a year to zero.”
Improving soil condition has also helped reduce run-off. Mr Reeve swaps straw for 2,000t of farmyard manure from a local beef producer, as well as buying-in compost. “Soil health, flora and fauna, works as they do the cultivating for me.”
Cover crops including stubble turnips, which will later be grazed by sheep, and phacelia with burseem clover are also being grown on the farm to improve soil quality.
Currently there is a six-metre wide buffer strip between cropping and the river, also contributing to water quality, however, Mr Reeve is doubtful about the future of this given the conditions of the new Countryside Stewardship Scheme. “I can’t see how we can comply with 800 pages of rules. It’s a shame. What do we do next, kill all the wildlife we’ve spent the last 25 years encouraging?”