Band spraying glyphosate between rows of oilseed rape drilled at wider spacings can be just as effective in controlling weeds as blanket spraying herbicide, according to new research.
These are the interim findings of an HGCA-funded three-year project, now in its final year, looking into new approaches to weed control in oilseed rape.
The project aims to find carefully directed control methods between crop rows to minimise reliance on residual herbicides.
“We are trying to develop these methods so that if we get restrictions over the use of propyzamide, carbetamide and metazachlor, the technology will be there,” says lead scientist Mark Ballingall, of the Scottish Agricultural College.
An early application of glyphosate, at the one-to-three leaf stage, was the best way to minimise damage to the crop – as beyond this point, oilseed rape leaves can grow to fill the inter-row spaces.
“The best results are coming from earlier timings when the crop is at one-to-three-leaf stage,” says Mr Ballingall.
“It gives you the maximum chance of keeping the glyphosate off the crop – if it gets in the crop, it will kill it.”
This technique allows the crop to compete with weeds that are growing in the rows, he adds.
Mr Ballingall says planting oilseed rape in wide rows initially reduces crop competition with weeds in the inter-row gap compared with crops grown on conventional spacings.
“But because the rows are sprayed with glyphosate, the banded crop acts as its own weed killer.”
Trials conducted in the field have shown that applying glyphosate through narrow, even spray nozzles (25 and 40 degree) and the shielded Micron Varidome system were the most effective at reducing crop damage.
Project partner Ron Stobart, head of crop research communication at NIAB TAG, says The project is looking into vision-guided techniques and GPS guidance systems to provide more accurate band spraying of glyphosate.
“Using some of the more promising delivery systems, we’re not seeing any appreciable damage to the crop.”
These techniques could prove invaluable for safeguarding products such as Kerb (propyzamide) and Carbetamex (carbetamide) to control problems weeds, such as blackgrass, in the future.
“We know the value of these products for controlling blackgrass and products are coming under increasing scrutiny,” he says.
“Therefore, we need to look at novel approaches to hold on to these essential products.”
“You can apply glyphosate at the crop as a desiccant, but in theory you still cannot apply it between rows for early weed control timing,” he explains.
One disadvantage of band spraying glyphosate is the potential need to follow up applications due to a second flush of weeds, he says.
And although applying glyphosate this way is effective, there could still be a need for targeted doses of propyzamide and carbetamide to control blackgrass, he adds.
Mr Ballingall reckons the technique could be developed to spray a low rate of active ingredient directly onto the crop where it is most needed.
“Instead of applying 1.5l/ha of metazachlor over the whole crop, we could apply a third of that just in the bands,” he says.
“By only applying herbicide to a third of the crop the potential for chemicals leaching into watercourses is reduced.”
Shielding design is also being looked at in crops to find the optimum shielding to prevent the spray from reaching crops.
“We are trying to establish a balance between achieving good weed control and minimising crop damage,” says Paul Miller, application specialist for NIAB TAG.
“This is directed by the width of the band and how far we can push the crop back into the row at the time of treatment.”
Shielding could play an important role if the techniques are introduced on farms, particularly at later growth stages, notes Dr Miller.
“At early stages you have a wide band because the crop is relatively small and you may not have a big germination of weeds,” he says.
“But at later stages, you might need to use shields so that weeds on the edge of rows can be treated without damaging the crop.”
Using a more comprehensive “all-around” shield at the two-to-three and five-to-six leaf stage will be trialled in the autumn.