Sprayer operators will need to follow best practice guidelines if they hope to see good grassweed control after switching to nozzles featuring drift reduction technology (DRT), trials by Agrii reveal.

“Our work and that of others has repeatedly shown that the optimum water rate for pre-emergence herbicides is 200 litres/ha.  At this rate with a flat-fan nozzle we achieved black-grass control of 88%. Change to a Defy 3D nozzle and control improved to 93%,” explains David Felce, Agrii agronomist. 

The difficulty in seeking to maintain high-level control comes with maintaining compliance with drift control regulations. 

“Sadly, getting the best from a product and controlling drift tend to be mutually exclusive choices, but through other measures it is possible to bring performance back to levels seen with older nozzles, such as the flat-fan,” says Mr Felce.

The advantage of DRT is that it enables a smaller buffer zone, typically 6, 12 or 18 metres depending on the product label, and this is considered preferable to the 30 metres from the top of the bank where no DRT is used. 

DRT compliance means using nozzles with a minimum three-star rating, such as the BubbleJet range from Billericay Farm Services and the Syngenta Amistar (Guardian Air) nozzle.

Unfortunately, most three-star nozzles are not rated for use at field pressures, typically 3-bar, which means growers would cease to be regulatory compliant. 

To overcome this, Agrii has been looking at four-star nozzles, i.e. 90% drift reduction, because even at pressures where they are no longer four-star rated, they still hold three [stars].

But this is far more than a compliance issue. Agrii trials at Stow Longa found that control fell by nearly 10% after switching from a Defy 3D to a three-star DRT nozzle and by nearly 50% when three-star nozzles were used at 100 l/ha and at pressures beyond their designated rating – see figure 1.
 

“The effect of DRT nozzles is to have fewer droplets, at which point surface distribution and retention become important to success.

We see that Backrow, a mineral oil adjuvant, helps to normalise droplets to create a consistent distribution across the spectrum.

When conditions deteriorate, this is a highly effective and easy way to support performance,” says Mr Felce.