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Changing tactics to optimise pre-em herbicides

During a season where wet weather and strong winds have prevented many growers from applying pre-emergence herbicides in good time after drilling, a Syngenta survey has highlighted ways in which sprayer operators can increase the number of spray days available to them, while also improving the efficacy of the products being applied.  

Abby   Kellett

Abby   Kellett
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Changing tactics to optimise pre-em herbicides #clubhectare

The survey, which was completed by more than 50 sprayer operators, showed while 11.3km/hour was the average operating speed of sprayers applying pre-emergence herbicides, about 20 per cent of operators have been exceeding the 12km/hour maximum which trials have shown could significantly reduce drift and improve weed control.


A further 15 per cent of sprayers had been operating at a standard boom height of 60cm or more – up to 80cm in some instances.


James Thomas, Syngenta application specialist, says: “Lowering boom height to 50cm above the target soil surface can prove the biggest single factor in reducing drift and optimising soil surface coverage. Allied to boom height, if operators slow down to less than 12km/hour it can hugely improve boom stability and help to ensure consistent height with an even spray pattern.”


Nozzle choice can also make a big impact on ensuring spray reaches the target soil surface, according to Mr Thomas, but the survey showed nearly 20 per cent were still operating with standard flat fans for most of their pre-emergence application and less than 10 per cent had been using drift reduction nozzles.


“Historically, operators have avoided low drift nozzles for pre-emergence applications. However, our black-grass trials have shown new nozzle designs, operated at appropriate water volume and speed, can achieve control levels as good, if not better, than 3D nozzles.


“If conditions are in any way compromised, the advice is to switch to 90 per cent drift reduction nozzles. Our application trials have shown flat fan nozzles really have no role for pre-emergence treatments,” he adds.


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Tips for effective pre-emergence herbicide application


  • Set the boom at a maximum height of 50cm
  • Do not exceed a forward speed of 12km/hour
  • Opt for a water volume of 200 litres/hectare
  • Use 90 per cent drift reduction nozzles
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