Young blackgrass plants© Tim scrivener

Blackgrass germination is likely to be slow this autumn meaning growers will have to be extra patient if they want to get good levels of control from stale seed-beds prior to crop establishment.

Testing has confirmed 2016 is a high-dormancy year for blackgrass, which means the grassweed will take longer to emerge before growers can spray it off. 

In fact, test result concluded blackgrass dormancy this year is at its highest since 2012.

See also: How growing winter barley cuts blackgrass numbers

While this has the potential to decrease the effectiveness of stale seed-beds, Adas weed expert Sarah Cook says the lack of moisture may be the key factor affecting germination this year.

In low-dormancy years, seeds will germinate rapidly in a moist, stale seed-bed, which helps growers reduce the blackgrass population before crops are drilled.

Blackgrass samples collected this year had an average germination of just 22%, compared with last year’s 33%.

Dr Cook explains the high dormancy is due to the cold period experienced during plant maturity from 11 to 30 June.

During this period the mean temperature during this period was slightly cooler (-0.16C) than the long-term average. 

However, Dr Cook points out this can vary with local conditions.

“Of the samples tested, some samples showed lower and higher levels of dormancy, indicating that local conditions were still important, but there were no obvious regional differences.”

She adds that dormancy applies only to freshly shed seed and the effect of dormancy may be minimal, depending on the amount of seed that is already in the seed-bed.

Patience

Independent agronomist Matthew Paterson says his part of Essex has seen very little rain and the lack of soil moisture is holding back any significant blackgrass chit.

He argues that there is always going to be a degree of uncertainty when it comes to blackgrass dormancy.

“It really depends when blackgrass seed was taken for testing. Low-dormancy seed tends to be produced when blackgrass plants are maturing in hot, dry conditions and high-dormancy seed is produced when plants mature in cold, wet conditions,” he explains.

This means that while the cool, dull months of June and July may well have caused blackgrass plants to shed seed that is highly dormant, any plants that matured in the warm August temperatures could potentially have produced less-dormant seed.

Waiting game

Midlands-based agronomist Luke Wheeler of independent crop consultancy group Indigro says the higher dormancy this autumn means growers with blackgrass will need to play the waiting game.

He notes while there isn’t much blackgrass coming through in his area of Leicestershire right now, but with recent rain this could all be about to change.

“I don’t think this actually has anything to do with it being a high-dormancy year, it’s more related to the very dry conditions seen recently.

“Now we’ve had some rain this may well change.

“I think it will be an issue this year with prolonged blackgrass germination throughout the season.”

He says growers can take simple measures to help mitigate any impacts of highly dormant blackgrass, with delayed drilling being a vital tool.

“Growers are trying to push drill dates back now anyway, because those who have got blackgrass should be doing this regardless of seed dormancy.”

Pre-emergency sprays

Achieving a good seed-bed will also help to get the crop off to flying start and Mr Wheeler adds growers will be relying more heavily on getting a good pre-emergence herbicide spray on, which should lead in to a period of strong residual efficacy.

He adds growers need to remember blackgrass dormancy testing is only relevant for weed seed that has been shed this season and does not bear relevance to seed from previous seasons that may be stimulated to grow by cultivation or moisture.

In Herefordshire, independent agronomist David Lines is reporting flushed of blackgrass after rainfall in the past week and in north-west Lincolnshire, grower Malc Parr says he is even seeing significant blackgrass flushes on undisturbed land post-harvest.

Growers and agronomists are reporting that blackgrass is now starting to emerge on land across the country.