Application covered for potato seedbeds
Bare soil, and potato seedbeds in particular, pose a serious challenge for herbicide application.
Whilst contact herbicides need to hit emerged weeds, the residual element requires a consistent coverage across the soil surface. Spray drift and boom height are critical components of achieving an even result, advises Syngenta application specialist, Harry Fordham.
Any shift in the spray pattern, frequently caused by gusts of wind, can affect the coverage of residual herbicides.
Defy trials, for pre-emergence grass weed control, has shown that even when spray conditions were deemed ‘ideal’ at an average 1.6 m/sec, gusts of between 0.5 to 8.0 m/sec during application resulted in up to 20% differences in levels of control with standard flat fan nozzles.
Application using angled 90% drift reduction technology (DRT) nozzles achieved far more consistent results, with higher levels of weed control.
Furthermore, with potatoes grown on deep ridges and beds, there is added effects of boom height and potential for shading on the windward side of the ridge.
Syngenta application trials have demonstrated that the angled 90% nozzles can be more adept at maintaining spray pattern, and resulting weed control, at a range of boom heights, compared to flat fan or standard variable pressure nozzles.
The research revealed that whilst black-grass control from flat fan nozzles dropped by 11% with a boom height of 100 cm (64% control), compared to the ideal 50 cm (76%). The angled 90% DRT nozzles gave consistently better results, with 91% and 84% of control at 50 cm and 100 cm respectively.
New nozzle technology to limit the effects of drift would also help to achieve improved coverage of both sides of the ridge and faces of potato beds.
Trials have also shown using a water volume of 200 l/ha has delivered consistently better results, compared to lower rates of 50 to 100 l/ha.
Also, trials for the pre-em herbicide application campaign: Go Lo, Go Slow, Get Covered, have highlighted the improvement in results from applications at 10 to 12 km/hr, compared to 16 km/hr or faster modern sprayers are capable of achieving.
Slower speed significantly reduces turbulence that can increase risk of drift, along with improvements in boom stability to maintain a constant 50 cm nozzle height above the seedbed. Additionally, maintaining slower speeds, along with nozzle size selection, typically enables delivery of the required water volume at lower pressure that minimises production of drifty, fine droplets and increases the proportion of large droplets that better hit and cover the soil surface.