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Autumn 2016
BLACKGRASS NEWSLETTER
A planned approach to grass weed control
In some areas (particularly Kent), the current dry conditions show no sign of changing, presenting a challenge for encouraging grassweed germination in a stale seedbed. It is important to remember the building blocks of any grassweed control program start with a sensible rotation and in maximising opportunities to disrupt the weeds and the seedbank between crops.
Stale seedbeds
Evidence from NIAB TAG work in the last few years has indicated that in dry conditions, seed loss through natural mortality and degradation may be REDUCED by cultivating, as burying the seed actually protects it; that is to say we might be better off not cultivating at all in dry years.
We cannot pre-empt the weather between now and drilling however, and stale seed beds – where recent rains have arrived – are still a highly effective tool.
Seedbeds should be worked from the top down to minimise clod size, and should be rolled immediately to break clods and conserve moisture.
Note that where Bromes are the dominant grassweeds, different tactics may need to be employed. Sterile Brome should be ploughed or immediately cultivated to encourage germination, however Meadow, Rye and Soft Brome should be left on the surface for a month to ripen, in order to prevent the seed becoming dormant.
Herbicides
Following on from creating a good stale seedbed, those efforts can be wasted by not spraying off all of the Blackgrass.  Ensure a complete kill before drilling, but:
  • Use an appropriate dose of glyphosate (540 gms/Ha minimum) & ensure seedbeds are sprayed as close to drilling as possible (ideally within 24-48 hours) to maximise pre-sowing blackgrass control
  • Take steps to avoid shading of the target - particularly with rape volunteers, by ...
  • Using angled nozzles
  • Aiming for a medium to fine spray quality, and reducing forward speed
  • Spraying off twice if necessary
Post drilling, ensure a fine, level seedbed to minimise Blackgrass germination from within clods.  Again, appropriate nozzle choice can belp to improve spray deposition in cloddy seedbeds.  Where seed beds are exceptionally dry, consider delaying the pre emergence herbicide to the peri-emergence of early post emergence timing to maximise the persistence of the chemical.

Always ensure that the seed is well covered by at least 4cm (1 1/2 ") of settled soil, particularly when aplying Avadex granules (DON'T apply Avadex if seedbeds are coarse/hollow & seed is visible). 
Balancing cultural control techniques
As ever, do not be in a hurry to drill the fields with the highest Blackgrass populations early; later drilling – even early October – means more time to spray off a flush of weeds, but also improves the persistence of residual herbicide. Take a sensible approach with seed rates to ensure adequate crop competition, particularly on areas of the field where establishment is usually poor.
Recent work has highlighted the benefit of adding glyphosate to pre emergence sprays, even in the absence of any visible Blackgrass seedlings on the surface. THIS SHOULD ONLY BE DONE BEFORE GERMINATION, AND EXTREME CARE SHOULD BE TAKEN TO AVOID CROP DAMAGE OR LOSS.
Where there is a very short interval between one crop being harvested and the next drilled, there is a strong argument for minimising soil disturbance and weed germination. This of course assumes that the soil structure is good and no remedial action is needed, but it is eminently possible in a dry maize harvesting season for example. 
Although tempting in cloddy seedbeds where slugs are appearing, do NOT roll after the residual herbicide has been applied.
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CCC LTD · MANOR FARM · DONNINGTON · CHICHESTER, SUSSEX PO20 7PL · United Kingdom

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