Article from Agronomist & Arable Farming Magazine
Pre-emergence herbicides are now the cornerstone of programmes for the control of
black-grass and other grass weeds in cereals. With many of the worst affected fields still
to be drilled, Agrovista’s Mark Hemmant offers some expert advice on getting the
best from these all-important sprays
Herbicide choice, seedbed quality and soil moisture levels are all crucially important in achieving high levels of weed control. But one factor often overlooked is the importance of application technique. Agrovista Select agronomy trials have investigated the influence of different pre-emergence application methods for 15 years. These show that using the correct technique can increase the level of grass-weed control by up to 50%.
While conventional small-plot trials using handheld booms are good for pesticide registration trials, they are usually applied at 3.6kph using a handheld boom 35-50cm above the target and achieve perfect soil coverage. Our pioneering work using our self-propelled trials sprayer enables us to develop novel, practical application techniques to boost efficacy and sprayer efficiency.
Agrovista has pioneered research into spray application
Our unique trials sprayer enables us to assess herbicide efficacy replicating current farm application methods and to develop novel techniques to improve both herbicide and sprayer efficiency (ha/hour).
Practical problems associated with pre-emergence herbicide applications include:
Lack of crop canopy increasing spray turbulence beneath the spray boom, resulting in poor soil coverage;
Boom heights usually raised to 70 or 100cm above the soil surface to avoid damage increase drift potential;
Poor fan angle and spray pattern associated with drift-reduction nozzles operated at low pressure.
Reduced water volume applications increase ha/hour treated but reduce efficacy.
Influence of boom height and nozzle choice on herbicide efficacy
Studies over the past five years have shown that, irrespective of nozzle choice, raising the boom height from 50 to 100cm reduces herbicide efficacy. This is because increased spray drift and turbulence beneath the spray pattern results in poor soil coverage and weed control. The effect on herbicide efficacy can be dramatic. Without the inclusion of Remix, control was reduced from 75 to just 44% with a variable pressure 80-03 nozzleSingle spray line application techniqueTrials over several seasons have shown that the most consistent method of applying preemergence herbicides for the control of low to medium populations of grass weeds is to use a VP 80-04 (red) nozzle applying the herbicide in 200 litres/ha at 3 bar pressure at 10kph. Alternating forward-facing (30º) fans with vertical fans along the boom increased the level of control from 75 to 92%.
Dual spray line application techniqueTo improve sprayer efficiency (ha/hour) the use of a second spray line along the boom enables higher water volumes to be utilised, increasing herbicide efficacy while maintaining forward speed. Each spray line applies 150 litres/ha via VP 80-03 (blue nozzle).In the trial below a combination of Trooper (pendimethalin 300 g/litre + flufenacet 60g/litre) at 2 litres/ha + Herold (DFF 200g/l + flufenacet 400g/l) at 0.3 litres/ha was evaluated through single and dual line techniques. The level of control ranged from 38-80% depending on application method – with the same herbicide!
Reducing the water volume from 200 to 100 litres/ha reduced the level of control from 60 to 38%. However, when applied via a dual line system in combination with Remix, efficacy was increased to 80%.