While the wet and cold start to spring favoured black-grass survival, there are several factors which have led to high black-grass populations this season, according to Hutchinsons technical manager Dick Neale.
To ensure black-grass is better controlled next season, Mr Neale urges growers to conduct an immediate post-mortem to help recognise what went wrong and why.
He says “Ask was the wrong choice of cultivation made? Was the field returned to winter wheat too soon? Was it drilling a bit too early or missing out the pre-drilling glyphosate? Was there a delay in pre-em application?”
He highlights some to the most common mistakes he believes were made this season.
- Underestimate of seed return from head numbers in 2017
“Although head numbers were relatively low last year, some growers did not appreciate the level of seed return you can get from a low number of black-grass heads. “We are told all the time by growers ‘I don’t really have black-grass’ or ‘I have it at very manageable levels’, but they are not really putting any prevention measures in place to deal with the low populations they currently have.”
Where there was a lock of robust control measures put in place, Mr Neal says growers have been shocked at what a few surviving plants seen in February can morph into come June.
- Failure to abandon first wheat aspirations after infested OSR
Typically, black-grass can develop most easily in OSR crops, according to Mr Neale, because of its ability to go undetected for much of the season. Growers tend to get caught out by one of the two forms of black-grass which can exist in an OSR crop.
“Firstly, you get the early survivors which establish in early September – they tend to be deep rooted and might have survived the pre-emergence stack because of things like shading. Their deep roots tend to allow these plants to overcome post-emergence Kerb applications.”
Black-grass plants presents this early in the season can produce about 40-60 tillers throughout the course of the season, says Mr Neale.
“And then you have black-grass which emerges in February. Growers don’t really tend to walk OSR Crops by this point in the season as the canopy is largely closed. Late emerging black-grass will still produce a head at this late stage, it may be a small head or a single stem, but if growers get lots of heads under the OSR canopy it could cause problems if undetected.”
He suggests growers inspect OSR stubbles as soon as the crop has been harvested to assess whether there are any large areas of black-grass which need to be managed.
For many, winter wheat is the favoured crop to follow OSR.
However, Mr Neale says too many growers have been guilty of sowing wheat into fields with high levels of black-grass infestation which have been allowed to develop in the preceding OSR crop.
He says “Farmers are very reluctant to abandon plans for a first wheat because often that is the crop which is giving them their best return, but tough decisions have to be made to get on top of the problem.
“For the very worst infected fields, a plan of two spring barleys or a three or four year grass ley are in reality, the only viable options.
Our work at Brampton has established that while a spring wheat may be a viable crop with far less black-grass return than in winter wheat, it still returns seven times more seed that a spring barley crop – making it unviable as a long-term control solution.”
- Ploughing up dormant seed
For some, ploughing is the ‘go-to’ option when black-grass populations appear to be getting out of control, says Mr Neale. But in attempting to bury the seed, growers not only run the risk of bringing up more weed seed than they plough down, but the extended dormancy associated with the weed seed they bring up is likely to make it more difficult to control.
Instead, he recommends leaving the soil undisturbed until the end of September.
“Germination does not commence in significant numbers until mid-September, so leave seeds on the surface during August and September as if it is dry they will degrade in sunlight and be predated, if wet they will grow readily on the surface and be predated.”
When cultivating the soil to promote germination, he recommends moving no more than the top two inches.
“Shallow tillage at 50mm will only move the very top layer of soil, thereby optimising the number of germinating seeds, but remember that too early a seedbed creation will result in too fine a seedbed for late October sowing or over wintering.
“If it is moist on the surface a double rib rolling will have a significant impact on germination, often increasing it by 50%,” he adds.
- Cherry picking the cultural control toolbox
Although it is important cultural control measures can be integrated with current farm practices, too often growers ‘cherry pick’ the cheapest or easiest options, which are least effective in controlling black-grass, maintains Mr Neale.
“If I was to list cultural control measures in order of importance, the first one would be drainage, then rotational changes to spring cropping, the third would be cultivation practices followed by later drilling, higher sowing rates and variety choice.
“Growers like to cherry pick the bits which are less painful to apply, which tends to mean picking options at the bottom of this list, despite the fact those higher on the list could have a much bigger impact.”
- Failure to apply residuals at true pre-emergence timing
Most growers are aware that pre-emergence herbicides work most effectively when applied within 48 hours of drilling, but often this timing is missed because of weather conditions or because drilling is prioritised over herbicide application.
Mr Neale says “For some growers the tractor which goes on the drill is the same one that goes on the sprayer, therefore things don’t get sprayed until they have finished drilling.
“If growers are unable to spray within 48 hours, it would be worth considering using a contractor,”.
Weather pressures and, in modern sprayers, isolation from the business end of the machine mean forward speeds and boom heights are sometimes misjudged.
“Anything faster than 12kph and a boom than 50cm can see control reduce by as much as 15-20%.
“Growers have to discipline themselves on the application of pre-emergence residuals because it’s a critical part of the control process,” says Mr Neale.