There’s a different nozzle among the spray tips on Steve Lake’s Bateman sprayer this year as he puts a design intended to optimise the application of pre- and post-emergence herbicides to new uses.

The FSOOTY 2011 award winner reckons the Defy tip’s characteristics also suit cereal fungicide treatments so, when conditions allow, it will be his nozzle of choice right through to T3 ear sprays.

Five different spray tips may get an outing at one time or another during the 10,000ha to 12,000ha workload that two self-propelled machines operated by Mr Lake’s employer Peter Knight at Burgate Farm get through on the home property and those of neighbouring farms through the Burgate Field Spray contracting service.

The 03 Syngenta Defy and a pair of Hypro GuardianAIR tips in 03 and 05 sizes will be used most; two 04 tips – a conventional flat fan and a Billericay Air Bubble Jet – are held in reserve of a high water volume application.

The five-way spray tip selection is being carried on a new Bateman RB35 sprayer this year with a shift from 24m to 30m boom width for increased output.

It has Norac ultrasonic boom height control, which is essential at 30m, he reckons, to cope with the undulating ground he sprays while keeping the boom at a height that minimises spray drift.

“Drift can increase hugely from using the boom at, say, 70cm rather than 50cm, so the sprayer needs a good height control system to keep the boom low,” Mr Lake says. “The Norac system is working well on the Bateman Contour boom, allowing me to spray at 12-13kph even on our most rolling fields.”

Spray drift is also the consideration that restrains operating speed for autumn herbicide spraying, even on level ground.

“I don’t like going too fast with autumn herbicides because apart from increasing the shadowing effect of clods, going beyond 13kph or so creates a vortex that encourages the spray to drift off,” Mr Lake explains. “You want a bit of forward movement so the droplets intercept the thin, upright target, but you don’t want it going off sideways because there’s no crop to catch it.”

Drift and shadowing are also behind the decision to switch from GuardianAIR 035 tips to the 03 Defy design for pre- and early post-emergence herbicide applications. It produces a 110° flat fan set at an angle, has a degree of pressure variation tolerance and is designed for use at 70cm boom height or lower.

For autumn herbicide use, it goes on the boom with the overlapping sprays alternating forward and back,” notes Mr Lake. “That eliminates the shadowing effect of clods, and puts spray on the back face of the clods themselves so the herbicide can still do some good if the clod breaks down.”

By eliminating the 25cm or so of unsprayed ground and using the Defy nozzle’s spray characteristics to minimise drift, Syngenta claims up to 30% improvement in control compared with a vertical flat fan.

A water volume of 120 litre/ha is typical for Defy (prosulfocarb) at a comfortable 12kph, rising to 140 litre/ha for Crystal (flufenacet + pendimethalin). But if the pressure is on to catch up with a workload delayed by poor conditions, then cutting the volume to 100 litre/ha and stepping on the gas to 14.5kph, will help get the job done while weeds are still small.

For oilseed rape treatments at this time, turning the nozzle holders to bring the 03 GuardianAIR into play exploits the canopy-penetrating capabilities of the larger droplets produced by this air-inclusion tip.

For the same reason, the tips are again arranged alternately angled forward and back – something that also appears to help minimise spray drift.

This tip also tackles spring herbicide treatments. Against the sizeable targets presented by cleavers and wild oats, the relatively large droplet size of the air inclusion nozzle versus a conventional flat fan again provides good canopy penetration.

“It’s no use increasing spray pressure in the hope of improving canopy penetration because all it does is create smaller droplets without the mass and inertia needed,” notes Mr Lake. “Forward angling the spray tends to improve penetration, as plenty of trials have shown, so that’s the arrangement I use if the weeds are just under the canopy.

“If they’re bigger and appearing above the canopy, I’ll alternate the tips facing forward and backward to get a combination of penetration into the canopy and dropping on top,” he adds.

In previous years, ideal spraying conditions would have seen a switch to an 03 vertical flat fan for the cereal fungicides, but the plan for 2012 is to go with the Defy nozzle when conditions allow.

“Previously, I’ve used the GuardianAIR for 90% of fungicide treatments because it can produce relatively small droplets for an air-inclusion nozzle, but with scope for reducing pressure and getting a coarser spray when it’s necessary to control drift,” notes Mr Lake. “Results have been good – but I’m convinced the Defy nozzle with its finer output will do the job, perhaps 60-70% of the time, in a decent year.”

The air-inclusion tip will continue to play a role when more effective drift control is necessary, he adds.

“Being able to get good drift control with a nozzle that can produce relatively small droplets is very useful when you have to strike a balance between spray quality and getting the fungicide on when it needs to,” says Mr Lake. “The GuardianAIR is excellent for that – but, of course, there comes a point when it’s better to park up than risk doing a less than satisfactory treatment through excessive drift.”

For T0 to T2 treatments, the plan is to use the alternating nozzle installation for both tips since the primary target area is either deep in the canopy to control stem diseases or part way down to keep the flag leaf clean.

A change of strategy is needed for T3 sprays, when the uppermost part of the crop – the ear – is the target.

“A forward angled tip will give too much penetration for this treatment, while a vertical spray can end up missing the ‘blind’ side of the ear,” Mr Lake explains. “A rearward angled spray will overcome that and by partly counteracting the forward movement of the sprayer allows fine droplets to settle where they are needed.

“In the past, I’d go with all the tips angled to the rear,” he adds. “But I may go for a half rearward, half vertical combination using the Defy tip when conditions are ideal and the GuardianAIR when they’re not.”