Getting the best out of Liberator for black-grass control

Pre-emergence herbicide Liberator (diflufenican and flufenacet) is widely acknowledged to offer excellent black-grass control, up to 80% where used correctly. Here are seven keys to maximising performance of the grass-weed killer:

1. Create the best possible seed-bed

A fine, consolidated seedbed gives sprayer operators the best chance of a good pre-emergence application. Cloddy seedbeds result in uneven applications and spray shadows that allow black-grass to continue growing.

Drill crops to a depth of 32mm to keep the crop’s roots well below the pre-em layer, which is typically 10-20mm deep.

2. Delay drilling to hit black-grass peak

Pre-emergence herbicides work best when their application coincides with peak black-grass germination – typically around the second week of October.

For those who normally drill in early September this may mean delaying drilling and the associated pre-emergence application by at least three weeks.

3. Apply at true pre-emergence

Ideally pre-emergence sprays should be applied within 48 hours of drilling for best efficacy.

Even onto dry soils, a true pre-emergence timing, although compromised will still be a better option than waiting for moisture and potentially letting grass-weeds germinate.

Applying herbicides three to five days after drilling is not true pre-emergence timing. Black-grass seeds disturbed by soil movement during drilling may not have penetrated the soil surface, but underground there may be root growth.

This means later applications require pre-emergence herbicides to penetrate deeper into the soil profile to get within the rooting zone of the black-grass. This takes time, if it happens at all, allowing black-grass to continue growing.

Where it is not possible to spray within 48 hours, application before crop emergence is the next best thing. Post-emergence applications typically show reduced grass weed efficacy.

4. Always apply at full rate

Liberator should always be applied at full rate (0.6 L/ha) when targeting black-grass, ryegrass or bromes, because 240 g/ha of flufenacet is needed to control these species effectively.

In difficult situations such as high populations or where there is resistance to post-emergence ALS herbicides, 240 g/ha of flufenacet should be considered as the base and extra residual herbicides added to this to boost control levels and ease pressure on post-emergence sprays.

A lower Liberator rate of 0.3–0.45 L/ha is appropriate for controlling annual meadow grass

5. Use appropriate tank-mix partners

The appropriate tank mix partners for Liberator will depend on various factors, such as target grass weed species, resistance status of grass weeds and other broad-leaved weeds present that require control.

Generally for mixed black-grass and brome populations the addition of extra diflufenican (up to 120g total) or the addition of 2 L/ha of Defy (prosulfocarb) to Liberator will boost control of these grass weeds.

Partnering Liberator with diflufenican also allows growers to use pendimethalin elsewhere in the programme.

Where previous resistance testing has shown up pendimethalin resistance, for example, it would be wise to use a non-pendimethalin containing tank mix partner.

For rye-grass adding flurtamone (as in Bacara), prosulfocarb or a sequence with Avadex granules will be useful.

In general, stacking chemistry by adding a second herbicide to Liberator at a pre-emergence timing will give approximately 5-10% better grass weed control.

But growers need to be cautious as stacking chemistry may increase the risk of crop damage. Particular attention should be made to seedbed quality, ensuring that seed is covered by at least 32mm of settled soil and, if possible, rolled before application. Do not roll after application.

6. Use sufficient water volume to achieve coverage

Residual herbicides are formulated to create a continuous layer of product in the top few centimetres of soil through which germinating weeds have to pass or are rooted within.

It is therefore crucial to use a water volume that allows you to get good soil coverage across the field. Provided the sprayer is set up correctly and ensures even application, 100 L/ha can be used, but application volumes of 200 L/ha are usually more effective at getting good soil surface coverage. Additional techniques such as angled sprayer nozzles can also help achieve even coverage of the soil surface.

The Liberator label advises water application volumes of 200–400 L/ha.

7. Apply using the best possible spray techniques

Sprayers must be set up and operated to deliver a sufficient concentration of product evenly across the soil surface for maximum efficacy. That means ensuring sprayers are tested under the National Sprayer Testing Scheme (NSTS), ideally every 12 months and carrying out basic maintenance through the season.

Check nozzles and ensure filters are clean prior to any application - spray out clean water onto dry concrete to check the spray pattern.

The performance of Liberator is optimised by:

  • Using a boom height appropriate for the nozzles selected
  • Angling nozzles forward and back to help reach both sides of clods
  • Using a medium-sized droplet
  • Applying in a water volume of 200-400 L/ha
  • Travelling at a maximum forward speed of 12km/hr to allow sufficient work rates without jeopardising coverage.

If the sprayer has been out of action for any length of time a static boom test is a sound investment.

  • Fully extend the booms
  • Set boom height to the appropriate height above ground level for the nozzles being used
  • Make a visual inspection for mechanical damage or faults
  • Check boom suspension by pushing down on each end in turn (the boom should bounce once before returning to its original position)
  • If your boom wobbles, check to see if the dampers need replacing
  • If the boom is slow to return to the start position, lubrication may be required
  • Check that pipes running from the machine to the booms are correctly positioned and in good order.

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