Wet weather and seed dormancy stifles blackgrass control

Well-developed blackgrass following first flush after wet conditions experienced in the West Midlands
Well-developed blackgrass following first flush after wet conditions experienced in the West Midlands

Recent wet weather has caused the first flush of blackgrass in many fields, increasing the pressure on some growers to consider drilling sooner than perhaps planned.

Blackgrass typically has two autumn flushes, the first at the end of September and another from mid-October.

In ideal conditions, the best time to drill is after the second flush, but wet weather may cause a change in tactics this autumn.

That will potentially increase the pressure on blackgrass herbicides, and make an effective pre-emergence programme even more important.

Bayer Technical Manager Darren Adkins thinks that some farmers may drill earlier than recent seasons to deal with the risk from wet weather.

He said: “We had 100mm of rain in Lincolnshire at the end of September and further rain in October.

“There is a balancing act between drilling later to control blackgrass and drilling earlier to ensure there is a good acreage of winter wheat crop, which on many farms is the most profitable crop.

“It will partly depend on the forecast, but I think the mindset has shifted to ‘when can I drill?’ from ‘how long can I wait?’.

“Particularly on heavy land farms I expect drilling to begin at the next break in the weather,” Mr Adkins said.

Further south in Oxfordshire, there are reports of a similar situation affecting farmers.

Blackgrass flushes finally began at the end of September after 50mm of rain fell in 7 days.

However, there has been less rain and farmers may delay drilling, Mr Adkins' colleague Ben Giles said.

“I expect most growers will delay until after mid October because they have first-hand experience of the difference late-drilling makes,” he added.

ADAS blackgrass seed dormancy forecast is predicting a higher-dormancy year, most likely pushing the second flush of black-grass towards the end of October.

Consequently, even in later drilled crops, there is a danger of further germination.

Mr Adkins and Mr Giles both agree that managing the risk with herbicides and establishment technique is 'essential'.

“The herbicide programme is going to be absolutely critical this season as the weather and dormancy are working against us,” said Mr Adkins.

“Proper timing makes a lot of difference at pre-em. Applying within 48 hours of drilling consistently achieves the best control from Liberator (flufenacet + diflufenican) in trials.

“In a wetter autumn, the big danger is drilling but not being able to spray because it turns wet, so make sure you can get back within 48 hours to spray.”

Other options to manage the risks include upping the seed rate to encourage establishment of a competitive crop.

Minimising disturbance at drilling can also help to limit the amount of black-grass germination in the crop, Mr Adkins suggests.