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Black-Grass: The Definitive Resource

 

Black-grass control is the biggest agronomic challenge facing most UK arable farmers. If you have black-grass, taking steps to reduce the population is key, while farmers fortunate enough to be free of black-grass need to keep it that way.

Controlling black-grass is a year-round task, using a wide range of cultural and chemical controls. The first step is to check populations, before planning crop rotation, cultivation and establishment technique. This is followed by a herbicide programme in autumn and spring to maximise levels of control.

Find out more about every aspect of black-grass control below, or use these quick-links to jump to the section you're interested in:

  1. Check your black-grass populations
  2. Use crop rotation to manage black-grass
  3. Choose the right cultivation technique
  4. Delay drilling and increase seed rates
  5. Maximise control with the right chemistry
  6. Black-grass resistance explained

 

Check your black-grass populations

June and July are the best times to check black-grass populations and plan your control programme. Black-grass plants are visible above the crop canopy, so you can take the time to note black-grass hotspots and count the number of plants per square metre. This, combined with testing seed for herbicide resistance gives you an idea of the extent of the black-grass problem and how to tackle it.

Immediate steps include patch spraying, hand-rogueing and harvest weed seed management. Looking further ahead, there is the opportunity to plan crop rotation, cultivation and establishment for the coming season.

In-depth advice

Use crop rotation to manage black-grass

Using your crop to manage black-grass is another building block towards total weed control.

Through crop choice, spring drillings, and delayed autumn drillings, significant improvement can be made in black-grass control.

When given the right conditions, crops can help provide their own weed control by competing with weeds for light and space. Higher seed rates, variety choice and drilling date can all push things in the crop’s favour, meaning herbicides can finish the job.

Crop rotation is also important to interrupt weed life cycles and prevent herbicide resistance. A balance of different crops will make it harder for stubborn weed populations to develop, while spring drilling will mean fewer black-grass plants germinate in the crop itself.

In-depth advice

Choose the right cultivation technique

Cultural controls are a vital part of an integrated weed management programme and put less pressure on chemical applications. Cultivation can eliminate black-grass before the crop is planted, as well as create a good seedbed for crop establishment.

Cultivation is determined by soil type, crop choice, available machinery and your own preference. There is no single cultivation solution for black-grass control, but there are a number of principles that are worth paying attention to – for example:

  • Burying black-grass seed through appropriate ploughing
  • Encouraging germination through stale seedbeds
  • Rolling after drilling

Choosing the right cultivation to suit the soil type on your farm (and the level of black-grass present) is a key part of control. Cultivations should be carefully considered; if not done correctly, they can accelerate the black-grass problem.

In-depth advice

Five ways cultural controls can help eliminate black-grass

 

Delay drilling and increase seed rates

Using drilling techniques to control black-grass can have a significant impact on weed burden. With 80% of black-grass weeds germinating between August and October, the later drilling takes place, the more time there is to get on top of emerging weed populations.

Postponing drilling until the second half of October will allow more weeds to flush and be treated with glyphosate prior to drilling, as well as reducing the number of black-grass plants that emerge in the crop. Increasing seed rates and minimising soil disturbance are also important tools for getting the best control in late-drilled crops.

In-depth advice

 

Maximise black-grass control with the right chemistry

Pre-emergence

Pre-emergence herbicides such as Liberator (flufenacet + diflufenican) are the backbone of black-grass control and, when paired with a solid programme of cultural controls, can prevent black-grass from stealing yield.

Liberator and other Bayer flufenacet products are little affected by resistance, and there has been no significant drop in performance in the decade since its launch. Flufenacet remains the most effective active ingredient for pre-emergence black-grass control, and when used in Liberator typically gives up to 80% control.

Additional control can be achieved by stacking or sequencing other actives such as pendimethalin, prosulfocarb and tri-allate.

 

In-depth advice

Four tips for getting the most out of pre-emergence herbicides in black-grass control

 

Post-emergence

Post-emergence herbicides are the final but vital step (other than potential rogueing) in an integrated black-grass control programme. They give the chance to remove plants surviving a pre-emergence treatment.

Contact post-emergence herbicides like Atlantis OD (mesosulfuron + iodosulfuron) and Monolith (mesosulfuron-methyl + propoxycarbazone) work by being absorbed through the leaves of the weed. Ideally, growers should look for opportunities to apply their post-emergence spray while the black-grass is still small and easier to control.

In-depth advice

Four tips for getting the most out of post-emergence herbicides in black-grass control

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Black-grass resistance explained

Understanding the types and mechanisms of resistance, along with how it develops at the cellular and field scale, can help you to develop an effective black-grass control strategy.

What exactly is resistance?

Herbicide resistance is defined as ‘the inherited ability of a weed to survive a rate of herbicide that would normally kill it. (Moss SR, 2006).

3 key criteria must be fulfilled for a plant to be classified as ‘resistant’:

  • Resistance must be heritable (passed on to offspring)
  • The plant must occur naturally and not be the result of deliberate/artificial selection
  • Resistance must be confirmed using acceptable scientific protocols

How does resistance spread?

Once a mutation has occurred, the trait (e.g. herbicide resistance) is embedded in the genetic make-up of the plant and can be passed to offspring. Only 1 plant has to survive and produce viable seed for the traits conferring resistance to be passed on to the next generation.

Beware the false alarm

It is worth remembering that several other factors could cause a plant to survive herbicide treatment; it may not always be due to resistance.

Other factors which must be eliminated first include:

  • Application problems
  • Rain after application
  • Too cold or too dry for herbicides to work
  • Germination from outside the zone of activity (pre-ems)

Resistance development at the genetic level

The repeated use of herbicides with the same mode of action has led to the evolution of resistant weed populations, but herbicides themselves are not to blame for causing resistance.

Natural gene mutations occur spontaneously in all plants and have the potential to change how proteins function. It is largely down to chance where any mutation strikes and how it alters that gene.

 

Inheriting resistance

The evolution and spread of herbicide resistance through subsequent generations is best explained by the Mendel theory of inheritance.

During the breeding process, the 2 alleles segregate during gamete production, with 1 allele going to the male part (pollen grain) and the other to the female ovum. If different alleles are present then 50% of gametes receive the dominant resistant allele while 50% receive the recessive susceptible allele.

 

Field-scale development and spread

During herbicide treatment, the active ingredient will only be effective against those individuals which are susceptible. Those which are resistant will survive treatment and be free to set seed and reproduce in following seasons.

Because black-grass is a cross-pollinating species, resistant genes can therefore be spread aerially in pollen, as well as via seed return in the soil.

Once resistant plants have established within a field, it can be relatively easy for seeds from these plants to be picked up and moved within the field by cultivation, harvesting or baling equipment.

Long-distance development and spread

It is possible for seeds from resistant plants to be picked up and transported longer distances by machinery, straw and manure, slurries or digestate, moving between fields or farms which can result in a wider geographic spread of resistant individuals.

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