Pre and post-emergence herbicide applications are vital to the control of blackgrass populations, but are only part of the solution when it comes to delivering a long-term answer to the blackgrass conundrum. 

That is the advice from Adama’s herbicide technical specialist, David Roberts, who, as the company launches its autumn 2018 crop protection knowledge hub, offers his advice to growers faced with the daunting task of controlling blackgrass in cereals and oilseed rape.

The latest Adama knowledge hub, titled ‘overcoming the blackgrass burden’, is available now via subscription at www.adama.com/uk.  It contains a wealth of useful information, all of which has been designed to enable growers to get a better understanding of how to deal effectively and efficiently with blackgrass in combinable crops.

“The key message throughout the hub is that there is no single measure which will totally eliminate blackgrass,” David Roberts explains.  “Instead, effective control is reliant on a combination of factors, with weed mapping, resistance testing, variety choice, rotation, cultivation technique and pre- and post-emergence chemical control measures all playing their part in an integrated approach.”

To compensate for the rising problem of herbicide resistance in blackgrass, David Roberts recommends the use of detailed weed mapping and resistance testing to ensure any chemicals that are applied are used accurately and are appropriate to the current weed population.   “Resistance amongst blackgrass populations to some of the key herbicide active ingredients is intensifying the challenge, so it makes sense to understand your enemy and to devise a crop protection policy accordingly,” David describes.

“Mapping blackgrass populations, either manually or via the use of modern drone or GPS technologies, and subsequently testing those weed populations for herbicide resistance will give growers a clearer understanding of the task at hand.*

“With the problem mapped and the enemy profiled, growers will be able to work with their agronomist to fine-tune their current crop protection protocols, thereby giving themselves the very best chance of overcoming the current blackgrass burden, whilst also laying the foundations for improved control in subsequent years.”

From a chemical control perspective, David stresses the need to make both pre and post-emergence herbicide applications.

“Growers are strongly advised to apply a robust pre-em herbicide within 48 hours of the crop being drilled,” he explains.

“The ensuing post-em application should be made soon after blackgrass plants have become visible (i.e. at GS 11 -12).”

With more than 15 active ingredients available to use against blackgrass, selecting the right combination of products can be complex.  “Flufenacet is regarded by many as the cornerstone active ingredient for cereal crops,” David explains, “but it’s efficacy can be improved by using it in combination with other compatible partner products.

“Adding Tower (250g/l chlorotoluron, 40g/l diflufenican and 300g/l pendimethalin) at the pre-em timing improves the efficacy of flufenacet, raising the level of blackgrass control from 60 to 70%.  With the addition of Avadex (tri-allate), the level of pre-em control can be increased to 80%.”

 Anthem (400g/l pendimethalin) is also a good option for blackgrass control.  “Compared to many CS formulations of pendimethalin, anthem’s SC preparation is more effective, and is a good tank mix partner option,” David adds.

In terms of blackgrass control in oilseed rape, David recommends an early season application of carbetamide to hit blackgrass seedlings when they are small and susceptible.

“A sequenced approach of an early (pre-em to 4 true leaves) application of Crawler (600 g/kg carbetamide), followed by propyzamide in Nov if/when a second flush of grassweeds has emerged will give oilseed rape growers the best chance of keeping ahead of blackgrass populations,” David explains.

“Where blackgrass populations are particularly high, a foliar graminicide should also be considered between the Crawler and propyzamide treatments.”

When used as part of a sequenced approach, an early season application of carbetamide can contribute to the cost-effective delivery of more than 96% control of blackgrass and has been proven to optimise the efficacy of herbicide programmes with propaquizafop and propyzamide.

It is also effective against chickweed and speedwell, with ryegrasses, meadow grasses and wild oats also showing susceptibility.

* To find out more visit about weed resistance testing go to www.adas.uk/Service/herbicide-resistance-testing or email weeds@adas.co.uk.