Trials show nozzle choice targets better weed control

Nozzle choice will have a fundamental effect on hitting the target and delivering effective coverage of the soil surface to get the best control from all pre-emergence applications, reports Syngenta application specialist, James Thomas.

Residual herbicides principally work via root and shoot activity, he pointed out. “Ensuring an even distribution of herbicide over the soil surface will improve your chances of controlling emerging grass and broadleaved weeds,” he advised.

James (above) warns that flat fan nozzles are typically highly sensitive to environmental factors, including wind speed, turbulence created by forward speed and boom height.

This can lead to uneven distribution of droplets over the target surface (see graphic) – which can result in areas of the target being unprotected by herbicide.

“However, 90% drift reducing nozzles produce a droplet spectrum that ensures better distribution of droplets on the soil surface and achieve the best results possible,” he advocated, “especially in less than ideal conditions.”

Results of new application trials at the Syngenta Barton Black-grass Focus Site have shown that 90% Drift Reduction Nozzles delivered consistently better results, compared to flat fan nozzles – especially in marginal spray conditions.

Using 90% drift reduction nozzles, operated at 50 cm boom height at 12 kph to apply 200 l/ha, delivered 10% improvement in black-grass control, compared to spraying with flat fan nozzles under the same conditions, operating at one meter boom height at 16 kph to apply 100 l/ha, 

Further research at the Syngenta Ryegrass Focus Site, in Yorkshire, demonstrated best practice using 90% DRT nozzles deliverd an even greater 15% improvement in control, compared to compromised performance with flat fan nozzles.  

“The key challenge for growers and operators is even within the constraints of following best practice, there are limited number of ideal spray days for flat fan application,” James pointed out.

Even on a good spray day there are frequently large variations in wind speed resulting from gusts. Weather station monitoring at Barton last autumn, on a near ideal spray day which had an average wind speed of 4 kph, highlighted there were only 2.25 hours where wind gusts were below 7.2 kph (below).

Measured at 50cm boom height, ideal conditions only occurred on 23 out of 60 days over the crucial autumn drilling period. 

90% drift reduction nozzles minimise the risk of drift. Wind tunnel testing at Silsoe Spray Application Unit has demonstrated how 90% DRT nozzles tested can mitigate against the effect of unexpected gusts during spraying, keeping product on target and maintaining efficacy.

“Given that the target is 97% control just to maintain grass weed populations, this highlights the importance of attention to detail with application technique to keep grass weeds in check,” advised James.