Cambridge, United Kingdom
May 27, 2014
With recent rain spurring on black-grass growth and development, now's the time to check populations and consider patch spraying with glyphosate advises Farmacy agronomist, Ryan Hudson.
Black-grass is flowering across much of the country, increasing the urgency with which growers need to map populations and, if necessary, take action to prevent seed return.
“Once black-grass flowers, it is quick to set seed and shed,” says Mr Hudson. “By the time we’re at seed formation, there’s a chance that glyphosate applications are too late; seed may still be viable when it hits the ground.”
Bayer CropScience trials field officer, Roger Bradbury agrees. “Growers have only a couple of weeks to get fields walked, mapped and where appropriate, sprayed off.
“Patch spraying is a drastic measure, but a useful one that aids resistance management and yield preservation in subsequent crops.”
There are a number of cases where Mr Hudson will be advising growers to sacrifice some crop to get on top of black-grass. “We’ve a couple of winter barley crops where we’ve poor control and some wheat crops where resistance, poor herbicide coverage or simple application misses are to blame.
“In all these cases, if the black-grass is left, the combine and cultivator will spread black-grass seed further across the field and we will have a much bigger area and population to deal with next year.”
Mr Bradbury and Mr Hudson emphasise the need to crop-walk with map and pen in-hand.
“Having an accurate picture of how much black-grass you’ve got and where it is, year-on-year, is really useful,” says Mr Bradbury. “While you can get a feel for what’s out there from the cab, nothing beats crop-walking.
“Where post-ems have been applied in the spring there is a chance black-grass has been stunted rather than killed - seed heads could be developing just out of sight below the crop canopy, ” he adds.
“The information gathered can be used for identifying trends in the rise and fall of populations, the efficacy of control strategies and, most importantly at this time of year, whether or not to spray off the worst areas with glyphosate.”
Mr Hudson says black-grass can indicate underlying problems like poor drainage and soil structure. Mapping these areas allows him to investigate and correct such problems after harvest.
“Black-grass maps can be overlaid on soil type maps and used when variably drilling - increasing the seed rate on known black-grass areas improves the competitiveness of the crop.
“Mapping can identify where we should prioritise stale seedbeds, scratching the surface immediately after harvest to get a flush of black-grass before any deep cultivations.”
“We cannot rely on herbicides alone, we must use cultural controls,” he says. “By mapping these problem areas now, when they are easy to see, we can be more focused with our management in the future.
Finally, Mr Bradbury points out that growers should not be too disappointed even where fields look dirty. “It is easy to forget how much black-grass is taken out with a full control programme. With trials it is easier, there is often a direct comparison but in field it is harder to see what has been achieved.
“Controlling black-grass is a ‘numbers game’ and where you’ve a high population to start with, it can be scary how much black-grass remains even when you achieve over 95% control.
“Achieving 98% control of a moderate population, 250 plants/m2 for example, still leaves five plants/m2.”
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