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LAMMA 2021

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Grass-weed management paying off

Concerted efforts to deal with problem grass-weeds appear to be succeeding across the country, reveals the latest in a series of national grower studies dating back to 2000. But the Roundup study conducted this spring also highlights a worrying slackening-off in the intensity of grass-weed management on the part of many which could easily reverse this progress.

Picture: Gary Naylor
Picture: Gary Naylor

The 2020 National Grass-weed Management Study, run with AgriBriefing, involved a total of 187 growers from across England, Scotland and Wales with an average arable area of around 250 hectares.

As with parallel Roundup studies in 2000 and 2016, it spanned a range of tillage regimes and intensities of challenge from all the main grass-weeds.

Bayer technical specialist Roger Bradbury says: “On a national basis, noticeably more farms report increases in black-grass and ryegrass problems today than in 2000, with a similar proportion finding increasing problems from brome.

“However, since 2016 there has been an encouraging decline in farms seeing increasing black-grass and brome problems.

Unfortunately, this is not the case with ryegrass, where the proportion of farms experiencing an increase in problems continues to grow (figure 1).

“Regional analysis confirms more growers have been seeing increasing ryegrass problems across all parts of the country in recent years.

“It also shows a clear reduction in the numbers with increasing black-grass problems in every region; particularly so in the West Midlands and Wales, and central and southern England.

“Eastern England and the East Midlands continue to be the worst affected regions, with growers reporting black-grass problems across half their winter cereals area, on average.

“Brome problems are particularly widespread in the East and North – across more than 20% of the winter cereals area on average – with southern growers having the most extensive problems with ryegrass.

“Wild oats remain a problem across a fairly consistent 25-30% of the winter cereals area and couch around 10%,” Mr Bradbury adds.

“Annual meadow-grass [which was not included in the 2000 study] stands out as problematic on more than a third of the northern winter cereals area, with many more farms here reporting increasing problems compared to 2016.”

Tillage differences

 

The latest Roundup study shows black-grass and brome continuing to cause markedly greater problems for those establishing their winter cereals with minimum tillage than ploughbased regimes.

This is not the case with ryegrass, however, which appears to be equally problematic across the different establishment regimes.

Herbicide resistance also continues to cause serious or very serious problems for many – more than half the farms involved as far as black-grass is concerned, around 20% with ryegrass and just over 10% with brome.

As in the past, resistant blackgrass causes the biggest headaches for those in the East and with min-till cereal establishment regimes, while those in the North, and basing their establishment on the plough, have the least issues.

Problems with ryegrass and brome resistance are more evenly spread across the country, although in both cases farms in the West report greater problems than most, as do min-tillers.

On average, growers are employing around six of the 12 main cultural techniques to control grass-weeds, the most widely used being rotational ploughing, spring cropping, delayed autumn drilling and stale seedbeds (figure 2).

The extent to which these individual techniques are being employed varies widely between different parts of the country and tillage regimes.

Unsurprisingly, stale seedbeds are far more widely used in min-till than plough-based regimes and, almost certainly as a result of this, in the East and South compared to the North and West.

Reflecting the generally greater weed challenges they are facing, more of those in the East and with min-till regimes are also employing spring cropping, delayed autumn drilling, competitive varieties and crop patch-spraying, in particular.

“Perhaps the best insight into recent changes in cultural control techniques comes from examining the practices of those facing arguably the greatest and least grass-weed problems,” says Mr Bradbury.

“It’s especially encouraging to see the extent to which growers with black-grass problems across half or more of their winter cereals area have stepped-up their controls in the past four years.

This is probably not unconnected with the decline we have seen in the proportion of farms reporting increasing problems from the grass-weed.

Overall, these growers are employing an average of eight main techniques today against 6.5 in 2016.

What is more, no less than 10 of the 12 main techniques are being used more widely than they were, with the other two only seeing a slight decline (figure 3).

Treatment

 

“Encouragingly, 97% are using at least one glyphosate treatment ahead of both winter cereal drilling and spring cropping, with more than half employing two or more sprays.

“However, those with black-grass problems across 25% or less of their winter cereals area appear to have slackened-off their cultural controls.

On average, they are employing only four of the 12 main techniques compared to more than five in 2016, and no less than 10 are being employed by fewer growers than before (figure 3).

“The marked increase in the use of rotational ploughing is a positive sign, adds Mr Bradbury.

“Thankfully too, the bulk of these growers are continuing to use a glyphosate spray ahead of winter cereal drilling and spring cropping.

However, almost a third aren’t applying any glyphosate even ahead of spring crops.

“As those who have ever suffered serious problems with brome or ryegrass as well as black-grass know to their cost, failing to bear down on these weeds sufficiently hard when they appear less problematic is a hugely false economy.

It really is vital people keep employing a range of cultural controls to support the chemistry as part of a long-term strategy to keep eroding the viable weed seed bank.

“Indeed, quite apart from the extent to which they reduce yields and interfere with management across the rotation, our latest study shows grass-weeds can easily be the difference between spending £60/ha/ year or less and £100/ha/year or more on winter wheat herbicides.” These worries are exacerbated by the study’s findings on growers’ current grass-weed management plans.

Encouragingly, those with the greatest problems are intending to step-up their cultural control efforts still further.

Compared to 2016, more are planning to drill more of their winter wheat later; improve stubble weed control; increase break cropping; make greater use of cover crops; reduce second wheat growing; employ higher wheat seed rates; and fallow more land, where necessary.

In complete contrast, noticeably fewer of those with the least problems today are planning to employ 11 of the 12 main control improving opportunities than they were in 2016.

Improving stubble weed control and growing more spring crops continue to be the most widely planned changes here.

However, the extent to which the planned use of these important elements has declined from four years ago is very concerning.

All the more so when accompanied by reduced intentions to both cut back on second wheat growing and delayed winter wheat drilling, in particular.

The National Grass-weed Management Study

The National Grass-weed Management Study

MORE than 180 growers from across England, Scotland and Wales took part in the 2020 National Grass-weed Management Study, run by Bayer in association with AgriBriefing.

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