Four-stage strategy keeps blackgrass under control

• Cereals grown on heavier clays

• Goal is to contain weed problem 

• Timely application still important

A four-stage strategy to control blackgrass is paying dividends for David Knott, general manager of Trumpington Farms, south-west of Cambridge.

Mr Knott uses targeted Avadex (tri-allate) as part of the four-stage management process which also includes cultural controls, sterile seed beds, improved cultivation techniques and stacking flufenacet-based selective herbicides.

The 3,500ha farming business grows arable crops on predominantly heavy clay with challenging drainage. Blackgrass was exacerbated by recent warm winters giving Mr Knott and his team a timely opportunity to reassess their control strategy.  

“Although we have worked extremely hard to reduce our overall blackgrass burden to a manageable level in most fields, its unlikely we will eradicate it completely. The whole issue now is one of containment and targeted control. 

“We have not had a grassweed herbicide with a new mode of action for decades now.

“A lack of hard winter frosts and snow has not helped either with nothing to kill off the autumn blackgrass or delay it from emerging again in the spring.”

Yield loss

Blackgrass remains a big contributing factor to yield loss – especially since the 2009 ban on isoproturon and subsequent resistance issues with ALS inhibitor herbicides. “It’s disappointing that very few genuinely new solutions have come forward since.”

Mr Knott says he had already widened the rotation to one in four for oilseed rape and improved cultivation techniques to limit the disturbance of any dormant blackgrass seed just below the soil surface.

He then made a key move to maximise the efficacy of Avadex by investing in an applicator to apply it as the crop was drilled – well within the key 48-hour post-drilling window.

“We had historically relied on contractors to apply Avadex granules post-drilling. However, working on 40m tramlines, we’d often found that our contractor, who used an 18m applicator, always left intermediate wheelings in the newly drilled crops.”

Own applicator

This became even more problematic if the work was done in wet heavy soil conditions, says Mr Knott. “The other big issue when using contractors was always delays, either due to poor weather or busy diaries.”

An Avacast GR400 applicator was purchased in September 2020. It was side-mounted on the 12m Horsch Sprinter drill for easier hopper accessibility when refilling. This meant raising the height of the Avacast for additional ground clearance.

Manufacturer Techneat Engineering designed a new bracket so the machine could be positioned exactly where needed. Although the applicator is specifically designed for  Avadex, Mr Knott says it can also be used to apply slug pellets when drilling rape.

“The machine is quick to set-up, easy to calibrate and uses a powerful hydraulic fan to deliver the Avadex to spreader plates positioned every 500mm along the full width of the drill providing double overlap and ensuring even distribution.”

Automated system

The Avacast GR400 comes with its own cab-mounted control box and manually operated on-off switch for headland control. Mr Knott then linked both these into a Trimble FmX guidance system, so it is fully automated.

“Our blackgrass control strategy is now essentially a four-stage process. We use medium or light-tine cultivation immediately post-harvest, then spray off any volunteers and remaining blackgrass with glyphosate to create a stale seedbed pre-drilling. 

“As we drill, we simultaneously apply diammonium phosphate placed under the seed and Avadex over the soil surface of the newly drilled seed. This creates a protective layer preventing any dormant blackgrass seed near the surface from germinating.

“We then apply two flufenacet based herbicides for pre- and post-emergence control of any later emerging weeds that get past the Avadex barrier.”