The last day that agrochemcials containing isoproturon can be used on crops is 30 September 2017. The herbicide active, better known as IPU, has been at the heart of weed control in winter wheat and barley for the past three decades.

Its loss from the market removes a simple, cheap, post-emergence option and forces a rethink on grassweed control. There have been many recent information meetings on alternative approaches and perhaps the main points are:

  • Pre-emergence will be essential.
  • Weed control will cost more.
  • Herbicides need a helping hand from alternative control techniques.
  • While growers will gravitate to an alternative chemical option, it is important to remember that control is becoming increasingly challenging.

    We now have little choice but to accept that resistance is all around us and it is likely to get worse. So weed control must begin by reducing the soil weed bank.

    This means shallow stubble cultivation and stale seedbeds. This is more important when troublesome grass weeds such as bromes, canary grass, resistant wild oats and blackgrass get a foothold.

    Deeside Agri seminar

    It was good to see the recent Deeside Agri seminar concentrated on cultural control methods. Practices such as stubble cultivation, stale seedbeds, good ploughing and later drilling can all help.

    Early drilling gives most advantage to the grass weeds.

    Planting date is reckoned to be the single biggest factor that favours blackgrass.

    This weed has been in parts of the country since the 1970s but it only became a serious problem since we began to drill early.

    Zero tolerance should be the objective for grass weeds so if something gets away in a crop, zap it with glyphosate.

    Reducing weed pressure

    Reducing weed pressure will not replace the need for herbicides, in the short term at least.

    There is general agreement that the best timing for the control of grass weeds is pre-emerge. The main actives for this purpose will be pendimethalin (PDM or Stomp), flufenacet (in Firebird) and prosulfocarb (Defy). All have strengths and weaknesses.

    With many growers having to chase difficult grass weeds, control could well involve two or even three targeted treatments.

    We have become familiar with this approach in recent years using Broadway Star for sterile brome control and a similar sequenced approach may now be needed for all difficult grass weeds.

    Where sterile brome is a serious target, we must remember that there are fewer post emergence options for barley.

    Because of this, many would say not to plant barley in a field that is bad with sterile brome. Alternatively, some might opt to put wheat on the headlands where this weed is likely to be worst.

    Using actives in products

    Growers may use these actives in products with other ingredients depending on the target weeds. Individual actives have long or short residual activity and this must be catered for in mixes and in programmes. PDM is regarded as persistent, as is DFF but flufenacet, prosulfocarb and picolinafen are short-lived.

    Products to use

    Pontos from BASF is a mix of flufenacet (240g/l) and picolinafen (100g/l) for pre- or early post-emergence treatment. At 0.5 l/ha, it supplies the 120g/ha of flufenacet that is regarded as essential for good grass weed control. Alternatively, 1,200g/ha of PDM is an equivalent treatment.

    Vigon is another new option from Bayer containing DFF, flufenacet and flurtamone.

    This is also pre-emerge or early post.

    While there are many specific products available, growers are likely to try to apply PDM just after drilling followed later in the autumn by products containing flufenacet or Broadway Star to tackle sterile brome. We must remember that specific products will better suit the needs of individual fields.

    Read more

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