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Grass weeds, particularly volunteer cereals and wild oats, will knock yield of OSR substantially.  ADAS trials show that 150 vol. cereals/m² can halve yield and just 20 cereals per m² can knock yield by 0.15 t/ha while 150 broad leaved weed/m2 will reduce yield by 8%.

Oilseed rape weed control key points;

  • Pre-emergence herbicide application normally gives the best broadleaved weed control. However no single product will control all weeds so a field specific strategy should be formulated to control the predominant weeds.
  • Where crops were sprayed for weeds in the autumn. A tidy up of grass weeds is still possible but options for broadleaved weeds are limited.
  • Clopyralid can be used before flower buds are visible but its weed spectrum is limited especially on larger weeds.
  • Graminicides may still be effective where vol. cereals etc. were not previously controlled. Consult the label as only some  of the graminicides are  recommended past flower buds visible stage, most can be used to the flower bud visible stage. 
  • Where crops are treated with aminopyralid i.e. Astrokerb the straw must be chopped back into the stub
  • Cleranda (Metazachlor 375g/l + Imazamox 17.5g/l) is approved for Clearfield Hybrid varieties only,  these are identified by the letters "CL" in their name and it should not be used on any other variety.

For details on specific herbicides contact your local Teagasc advisor.