Blackgrass dormancy very low this summer

The dormancy of blackgrass seed is very low this summer, meaning control could potentially be easier to achieve. In years with low dormancy and high germination, more of the grassweed emerges and can be killed before drilling.

Some 31 blackgrass seed samples were tested by crop consultant Adas and those not affected by orange wheat blossom midge (OWBM) saw the highest germination and hence lowest dormancy level for 18 years.

Sarah Cook, author of the report and weed specialist at Adas, says the presence of OWBM had significantly reduced the germination of many blackgrass seeds.

This may mean that despite high blackgrass populations, OWBM may have killed a high proportion of seed and emergence may be lower as a result.

See also: One grower’s plans for tackling blackgrass next season

Early blackgrass

Early blackgrass © Tim Scrivener

But the seven samples out of the 31 without any OWBM showed the highest germination rate over the past 18 years of testing at 80%.

Dr Cook says the key factor affecting germination this year will be moisture availability, and gives her advice for this coming season:

What to do in a low-dormancy year

  • Freshly shed blackgrass seed will emerge rapidly where adequate moisture is present.
  • Leave stubbles uncultivated – this allows seed to be predated and to germinate. Cultivations will bury seed, removing it from predators and can induce seed into a deeper dormancy. 
  • Use minimal or non-inversion tillage, keeping seed within the top 5cm, where it can germinate. Try to minimise bringing up old seed from previous years.
  • Delay drilling (no later than the end of October) to allow maximum weed emergence, as crop establishment will be compromised.
  • Spray off any blackgrass that emerge before drilling with the correct dose of glyphosate.
  • Apply a robust pre-emergence herbicide with a residual component within 24-48 hours of drilling.
  • Apply a robust post-emergence herbicide programme. Post-emergence sprays need to be timed after most blackgrass has emerged, applied at the correct growth stage and should also include a residual element.