Guidelines for Single Spot

Superseded on 14/03/2024 by this article

Optical Spot Spray Technologies OSST Label compliance

Refer to this typical OSST Label.

OSST Label

When it comes to spot-spray (OSST) nozzles, there are basically two types. Tapered fans and even fans. Most of my customers are sporting tapered fans so that is what I will be discussing here.

Spray zones

In calculating the rate for compliance purposes, the entire spray width for single nozzles in isolation needs to be accounted for. That goes for both even and tapered fans. The rate/ha will be the same, just the distribution of volume across the fan will be different.

See and spray calculator

Conveniently, 100 l/ha has been the basis of nozzle selection for most of you. With that part out of the way, what we now want to know is how the volume is distributed. i.e. the concentrated rate per h/a in the 50cm target zone.

We tested the Wilger MR80-08 (same spray quality as DR80-08) at 80 cm height. Simulated speed 16 km/h.

All zones

The results were;

See and Spray table

You can use the adjustment factor in the Spray-Width Adjustment box to come up with an adjusted rate/ha in the target zone;

For 70cm nozzle height;

For 80cm nozzle height;

Some other points for consideration are;

  • That weeds occurring in the taper-zones will be in the target-zone of the adjacent nozzles, and
  • Despite an elevated rate between consecutive activating nozzles, that sufficient overlap is a necessary feature in order to deal with tall inter nozzle weeds. I.e the height at which overlapping fan patterns intersect.

A reminder that the 50cm target-zone rate/ha delivered IS NOT the rate/ha of the sprayer. That would be to ignore and not account for a full 40% or so of the total volume in the taper zones actually applied to the paddock.

You could argue for an 06 nozzle which has the ability to achieve 100 l/ha in the target zone in similar circumstances. The overall rate/ha however is 68, not 100.

If you consider that a matter for interpretation then you have some numbers to work with. I hope you will find this information helpful and can apply it to your advantage.


Dave Young 08 6102 5886

28 February 2024

The LABEL is concerned with the amount of product on the paddock. YOU are concerned about the amount of product on the target - Dave

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