Dave’s Concise Fungicide Spraying Guide

This article is a follow up to our Twitter Poll asking the question of respondents about some of our popular nozzles and their suitability for some specific fungicide spraying tasks;

“Which nozzles do YOU THINK we’ll be recommending”

Well, here is what we are recommending. Please read on.

I think everyone will agree that THE MOST IMPORTANT issue when it comes to spraying fungicides is TIMING!

The next issue that arises is:

If I have to spray immediately, are the nozzles already on my boom suitable to spray the specific fungicide right now?

The answer is most likely going to have to be YES, regardless of what nozzles are on your boom. Waiting days for new nozzles is just not an option. Besides, you may have already used the current nozzles for fungicide applications already with a satisfactory outcome. If so, great! If it’s been working, keep doing it.

If on the other hand, if there is a high likelihood that fungal diseases may appear in your area and you are the type that prefers to plan ahead, then organizing a specific set of nozzles in advance to have on hand, “just in case”, (or to be already installed on your machine for general use) may be a smart move in helping to achieve a timely and efficient disease management regime on your farm. Or if you are a contractor, to be job specific for your clients benefit.

With the luxury of time on your hands, what are the main considerations when selecting nozzles to apply fungicides?

These are basic situations to be addressed;

  1. Achieving canopy penetration for cereal fungal leaf diseases or stem rot in canola, and
  2. Dealing with grain head diseases like Fusarium Head Blight.

Achieving Penetration and Coverage in Crop Canopy

Let’s keep it simple. As canopy density increases, you will benefit from more;

  • Spray Volume: 100 lit/ha is better than 70 or 80 lit/ha.
  • Pressure: A nozzle of Coarse Spray Quality at the mid to high end of its pressure range. (Not to “blast” the droplets in – myth, but to influence the droplet spectrum to contain a higher percentage of medium droplets for contact formulations).
  • Both subject to label recommendation and operational considerations.

My Nozzle Picks for improved penetration & coverage;

  1. CFA-T Compact Fan Air Tilt – Rear angled at >15 km/h compensates for forward momentum to minimize spray mixture applied to leading edges of canopy. Direct vertical path of droplets improves leaf coverage and penetration of medium droplets into lower canopy.

It’s no different to how they work in stubble!

  1. CFA Compact Fan Air - Next best option.
  2. We do not recommend twin-fans, either Air Induction or conventional, for dense canopy penetration. Lower boom heights become necessary to overcome loss of momentum, (30-degree angles requiring way more distance to reach target), which can be problematic with high speeds and/or rough terrain. Also typical VC, XC Spray Qualities of this nozzle type makes it more difficult to obtain sufficient medium sized droplets in the mix.

Achieving Optimum Grain Head Coverage

Again keeping it simple;

  • Large droplets in the C-VC range.
  • Aggressively angled twin-fan to attack back and front of target.
  • Medium spray quality to be avoided particularly in awned varieties as the awns tend to catch up the medium droplets preventing them from getting through to the target.

My Nozzle Picks for Optimum Grain Head Coverage

  1. ATP Air Twin Plastic, because it produces large droplets with aggressive forward and reverse angles.

#Note that if these can be angled backwards by 15-degrees for speeds > 15 km/h, a similar performance improvement can be expected as with the CFA-T Stubble Jet.

  1. CFA-T Compact Fan Air TILT (Stubble Jet), because this 13-degree angled nozzle, although less aggressive that the ATC, may be alternately directed in a crisscross pattern to emulate the twin-fan.
  2. We do not recommend the CFA specifically for this purpose, simply because the previous two options are way more suited to the specific task.

As an addendum, the following is to address a question that was raised in regards to our Fungicide Nozzle Choice Survey on Twitter.  The questioner quite understandably stated in regards to the specific nozzles we had named, CFA, CFAT (which typically have a Coarse Spray Quality) & ATP (Coarse to Very Coarse) and made the following comment;

“Hard to achieve Medium spray quality with these nozzles though.”

Thank you for raising the issue, and let me address it specifically here.  Since I have referred to “medium spray quality” a couple of times above, the valid question that arises is this;

Does “Medium Spray Quality”, mean the same as “medium spray quality”?

If it is the case that you want to achieve a Medium Spray Quality because the label requires it, that may or may not be possible with the nozzles you have. However, according to regulations, M and above, including C, and VC etc. are still legally *compliant for use.

That is not to ignore that if a Chemical Manufactures has put M on the label, then obviously an actual Medium Spray Quality nozzle would be ideal. Alternatively, the objective is to manipulate the droplet spectrum of the nozzle you do have to contain the highest possible percentage volume of medium droplets in the mix.

Let’s say the label says M.  Your nozzles at the rate and speed you intend to spray may be C according to the chart. What to do?

Firstly, understand that even low drift Air Induction Fan Nozzles produce a broad spectrum of droplet sizes. The current Spray Quality System is there mainly to provide a point of reference between Chemical Company recommendations and Nozzle manufacturers specifications for the purpose of drift control. For a thorough and detailed explanation on how the official Spray Quality ratings are derived, please read this article here: http://nozzleshop.com.au/articles/asabe

The Spray Quality Rating therefore is a great guide to nozzle performance however the rating itself provides no objective data with which to calculate the percentage volume components of F, M, C, VC etc. for any given nozzle. In some cases, this information may be available from manufacturers, however since the current system has been in place, manufacturers tend not to publish the detailed data in their catalogues, merely the Spray Quality Table.

To illustrate the point, take a look at this graph. It shows a different way of looking at Spray Quality compared to the tables that you will be used to seeing.

Follow the green line which is the 5 BAR curve. Note that it sits just on the Coarse side of the boundary between the Coarse and Medium rating without actually crossing it. If due to a small increase in pressure, the green line crosses over into the Medium zone, will that represent a wholesale change in the overall droplet distribution of the nozzle? Obviously not, although officially, it would have changed from a C to an M.

Conversely, if we opt for a more dramatic change in pressure. Consider a pressure increase from 3 BAR where on this chart the nozzle is a mid-range C up to 5 BAR which is still C, but as discussed above, on the cusp of M, moving the nozzle towards a more m’ish profile even though it’s not formally an M.

Again all of this is in the context of having an Air Induction nozzle that is not necessarily the formal Spray Quality that you would like it to be.

In conclusion

So, if you desire a medium spray quality, either because your label recommends a Medium Spray Quality and your nozzles are not officially M, but C or VC, there’s nothing stopping you from increasing your rate (label dependent) and pressure in order to push your droplet spectrum towards a more m’ish droplet mix to get the job done today.

Alternatively, if your label says C, you know that you can remain formally in the C category for compliance purposes, while going for a more m’ish spray quality for better penetration and coverage in dense canopy anyway.  So far as in canopy action is concerned, you’ll have it covered either way!

Finally, remember with fungicide applications, TIMING IS EVERYTHING!

If you prefer to plan ahead however, and have the optimum nozzle available if you need it, consider the old Boy Scout motto,

“Be Prepared” … with a set of Air Twin Plastic ready to go for pests affecting Cereal Grain Heads;)

And for everything else, just own a set of CFA-T Stubble Jets and be done with it!  Crikey, you can even crisscross them for spraying Grain Heads too!

Article by Dave Young

7 June 2017

Reference:

  • Australian Pesticides and Veterinary Medicines Authority - Spray Drift Labeling

https://apvma.gov.au/node/958

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