Nozzle Selection and Sprayer Setup


Achieving adequate spray coverage is critical
to the effectiveness of contact herbicides. Tom Wolf is a research scientist with Agriculture
and Agri-food Canada at the Saskatoon Research Station. His research looks at nozzle selection,
configuration, water volumes and pressures to help producers achieve the kind of spray
patterns and coverage required for optimum performance of crop protection products. Agricultural
spraying has undergone nothing but a revolution in the last ten years or so. Ten years ago
producers really only have one nozzle choice available to them and that was a conventional
nozzle that had a good track record of performance but also had drift issues. Since that time
they have, the industry has introduced low drift nozzles, air induced low drift nozzles
primarily. That have now reached a large segment of the market. In Western Canada for example,
our surveys indicate that up to fifty percent of producers are using air induced low drift
nozzles. Now that revolution has not under undergone without some growing pains. One
of the important issues has been that the nozzles can be used improperly resulting in
poor performance of the pesticide. So what I’d like to go over with you quickly is
about four for key rules of nozzle selection that help a producer decide what the right
nozzle is for their needs. And the first of those four rules is to spend some time making
the right selection in the first place. There’s a number of different nozzles out there and
You need to consult with and expert to identify the right nozzle for you. We’re going to be
spraying with the four major nozzle types that are available on the Canadian market.
The four types are the conventional nozzles which is the old standard, the pre-orifice
nozzle or low drift version, a low-pressure air induced nozzle and a high pressure air
induced nozzle. Okay we’re going to start with the conventional nozzle, an 80 degree
flat fan. This nozzle’s designed to work well between about 20 and 60 psi. We’re
spraying at 40 right now. When you go to lower pressures, pattern does collapse and the spray
gets coarser. When you go to higher pressures the pattern forms nicely, but it can become
very drift-prone. And that’s the problem with this nozzle. This is also a conventional flat
fan but it has a hundred and ten degree fan angle. The wider fan angle allows a wider
pressure range. For example, if I go to lower pressures, I can maintain a good pattern at
lower pressures than I could with the 80 degree nozzle. Problem with these tips is that they
get excessively fine at higher pressures, particularly the 110, more so than the 80.
So drift can become a real problem at these kind of pressures. This is a pre-orifice nozzle.
It uses a pre-orifice to reduce the internal pressure of the tip and that reduces drift.
You can see that there is less drift with this nozzle at the conventional pressure of
forty. When we go low we do lose the pattern a little bit more rapidly than before. And
therefore we have to actually elevate the pressure slightly in general. I’m at forty.
I’m at fifty; this is a good pressure range to operate these tips. At higher pressures
like all nozzles, they become more drift-prone but they never again reach that potential
that we had with the other tips. This is the low pressure air induced tip. It’s just like
a pre-orifice tip except it uses a venturi in the middle introduce air into the mix and
that makes the spray coarser. At 40 psi, much coarser than we’ve seen before. If we go
to lower pressures here, it becomes problematic almost right away, giving us an unacceptable
pattern. But if we go to the optimal pressure range for this tip of say fifty, sixty, seventy
psi. We reach a nice pattern. We get a nice spray that is fairly low drift, but still
provides the coverage.
Going back down to about forty psi. This is a high pressure air induced nozzle, this is
the same design as the low pressure except it’s designed to be even coarser and therefore
requiring even higher pressures. You can see how coarse this nozzle is compared to what
we saw before. It’s not designed to be operated at these low pressures but I’ll show you
what happens to the pattern. It virtually disappears. We should be well above forty
with these kinds of tips. Sixty, eighty psi is ideal. These nozzles even work quite well
at a hundred psi. The drift potential increases with higher pressures but it never goes as
high as it was with the conventional tip. The following demonstration illustrates the
range of coverages that can be obtained with modern nozzle selections. The first example
uses the conventional flat fan nozzle, spring approximately one hundred litres per hectare
at forty psi. The second example uses an air induction nozzle again spraying approximately
one hundred litres per hectare at forty psi. The paper on the left shows the results of
the conventional flat fan nozzle producing very fine droplets and achieving thorough
coverage. This spray would be very prone to drift. The paper on the right shows the results
of an air induction nozzle producing a courser spray that will be much less prone to drift
but achieves less thorough coverage. For some products, especially contact herbicides proper
efficacy may not be achieved with coverage like this. Using increased water volumes and
higher spray pressure will provide better coverage. Growers must decide the right balance
between minimizing drift and achieving adequate coverage based on the coverage requirements
for effective performance of the product they are spraying and their tolerance for drift.
Here is an illustration of the relationship between water volume and spray quality. Growers
can choose nozzles that produce droplets ranging in size from fine to extra coarse. Tom Wolfe
recommends growers double-check their sprayer performance by making an in-field pass over
water sensitive paper and comparing their results with this chart. Are your results
in the top left or bottom right? You can arbitrarily draw a line below which your results should
not fall, however you can’t draw a single line for all products. The line will move
depending on what you are spraying and your tolerance for drift. For products like contact
herbicides ensuring your spray pattern is similar to those towards the top left corner
is important for product performance. Using higher water volumes and the proper spray
pressures for your nozzles will help reduce efficacy issues with these types of products.
In conclusion then, the air induced low drift nozzle can be successful if you follow these
four rules. They are: spend some time selecting the right nozzle for your needs, consult with
an expert. The second rule, make sure operate the nozzles at the right pressure, often that
means a higher pressure, 60, 80 or 100 psi is not uncommon. The third rule is use the
appropriate water volume. If you go to a courser spray you may have to increase your water
volume slightly. And finally and make sure your pattern is appropriate. Oftentimes we
need a wider, a larger overlap underneath the boom compared to a conventional nozzle.
Research indicates that if you follow these four rules you will be successful using your
pesticides and protect the environment.

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