Do Labels Help us Apply Pesticides Properly?

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About Tom Wolf (Nozzle_Guy)

Tom Wolf is based in Saskatoon, SK and has 33 years research experience in the spraying business. He obtained his BSA (1987) and M.Sc. (1991) in Plant Science at the University of Manitoba, and his Ph.D. (1996) in Agronomy from the Ohio State University. Tom focuses on practical advice that is research-based to improve the efficiency of producers.

See all posts by Tom Wolf (Nozzle_Guy).

It happened three times this spring.  As is often the case, I was contacted by growers who wanted help with herbicide application.  In most of these calls, the discussion revolves around the proper choice of nozzles for a specific task, perhaps some questions on spray pressure, water volume and travel speed.

But these three were different.  Instead of being seasoned applicators, all three were new to the business.  And more importantly, they had done their homework by looking at product labels before calling.

Labels give us important information on product rates, crop and weed staging, mixing order, sprayer cleaning, and personal and environmental protection.  They’re very valuable there.  But they also provide application information, and that’s where the problems begin.

Perseverance Required

I have to commend my three clients:  they showed great tenacity by actually finding application information on a pesticide label in the first place.  This document is so mired in legalese protectionist language at the front that it discourages all but the most persistent.

And often, the application information comes in several parts, interspersed among other information.  Mixing instructions.  A little later, application. Somewhere nearby, buffer zones.  Another paragraph for cleaning.  Rainfastness?  Keep looking.

It forces the reader to skim through the document, hunting for relevant information.

But once my clients found application instructions, they obviously questioned if they should believe it, or else they wouldn’t have called.  The application statements on many labels, simply put, are from long ago, and it’s obvious.

Consider the following two label excerpts, the first from a product initially registered in the mid 1980s and still available, the second from one registered about 30 years later:


Application should be made using a minimum of 55-110 litres of water per hectare, at a pressure of 275 kPa, or 310 kPa if using check valves, and at a ground speed of 6-8 kph.

The use of 80° or 110° flat fan nozzles is recommended for optimum spray coverage.

Do not use flood jet nozzles, controlled droplet application equipment or Sprafoil® equipment.

Application of the spray at a 45° angle forward and higher water volumes will result in better spray coverage and penetration of the crop canopy.

Uniform, thorough coverage is important to obtain consistent weed control. Higher water volumes should be used under dense crop and weed canopies to ensure thorough coverage of the target weeds.


Apply in a spray volume of 46.8 – 93.5 L/ha unless otherwise specified in tankmix partner section of this label – at 207-345 kPa (30-50 PSI) pressure to ensure proper weed coverage.

Flat fan nozzles of 80° or 110° are recommended for optimum coverage.

Do not use floodjet or controlled droplet application equipment or Sprafoil® equipment.

Nozzles may be oriented 45° forward to enhance crop penetration and to give better weed coverage.

Uniform, thorough coverage is important to obtain consistent weed control. Higher water volumes should be used under dense crop and weed canopies to ensure thorough coverage of the target weeds.

Thirty years apart, but remarkably similar.

Crop protection companies spend about 10 yrs. and $250 million to produce a new pesticide and register it for use.  Having made this commitment, it would be most useful to see a small further investment to provide current application information that is relevant to applicators.

After all, these applicators purchase the active ingredient to provide a return on this multi-million dollar investment, to the tune of about 2 billion dollars per year in Canada alone. They deserve good application information.

Imagine this scene:

“Doctor, thank you for this new high tech pharmaceutical engineered to help me with my serious illness.  How should I take it?”

“Not sure.  Here, read this cough syrup label I found in my drawer.  Should be pretty close.”

It’s clearly ridiculous

Let’s dissect these labels to see how they could be improved.

Flat fan nozzles of 80° or 110° are recommended for optimum coverage…

Our sample labels refer to what we assume are conventional flat fan nozzles.  While popular in the 80s, these have all but disappeared from sprayers over the course of the past 20 years or so.  We haven’t recommended them since then because they drift too much. They’ve been replaced by low-drift nozzles, either pre-orifice, or air-induction.

Nozzle fan angles are now generally 110 degrees or more, and frankly, the difference between 80 and 110 degrees is not that important.  What’s important is proper overlap, achievable with a visual assessment followed by boom height and pressure adjustments.  Unfortunately the label is silent on that.

Application should be made … at a pressure of 275 kPa, or 310 kPa if using check valves…

A nozzle’s recommended operating pressure depends on the specific nozzle model and on the spray quality (average droplet size) required. With literally many dozens of nozzles now available to each applicator, general pressure suggestions are likely to be wrong, and are more of a liability than a help. And they force label non-compliance when over-ruled by a nozzle manufacturer’s recommendations.

Speaking of spray quality, growers crave to know at what spray quality a product should be applied for best performance and lowest drift. Some labels refer to spray quality (e.g. “apply with a Coarse spray”), but this is with reference to spray drift and buffer zone distances, not efficacy, and that distinction is not made.  Knowing the right quality for efficacy would help applicators choose the right nozzle and pressure to meet that criteria.

Higher pressures if using check valves?  Nobody has brass screens with check valves anymore.  Sprayers have had modern diaphragm check valves for a generation, and those don’t produce pressure losses.

And we all know that six to eight km/h is hardly a common speed these days.

Do not use floodjet or controlled droplet application equipment or Sprafoil® equipment

Sprafoil nozzles have not been produced in Canada for about 25 years, in fact their manufacturer is no longer in business.  Controlled droplet atomizers, while becoming more popular again on aircraft, were last seen on ground sprayers in the 1980s. Even then, total installed numbers were probably in the single digits.

As for FloodJet nozzles, those went out of style for herbicides in the late 70s, and were replaced by the very successful TurboTeeJet nozzles shortly after.

Nozzles may be oriented 45° forward…

Nozzles are rarely tilted 45 degrees forward for herbicide application anymore.  Maybe that’s because spray booms aren’t built that way today, or because modern booms on self-propelled sprayers are now about 30” (75 cm) above ground, and we travel at about 15 mph (22 km/h).  So the forward tilting, though shown to be effective for grassy weeds at 5 mph (8 km/h) and 20” (50 cm) boom heights, as researched in the 1970s, isn’t relevant for herbicides with higher booms.

Uniform, thorough coverage is important to obtain consistent weed control.

Statements advocating for good coverage are nice, but they aren’t useful.  Everybody knows we want good coverage.  What applicators need to know is how they should measure coverage, and what good coverage actually is.  Can we use water-sensitive paper?  How much of the target should be covered?  How many droplets should be in each square centimetre?  How can we measure that in the field, right now? How does it depend on the crop canopy, on weed stage, and on spray quality? The more information an applicator gets, the higher the chance of success.

Apply in a spray volume of 46.8 – 93.5 L/ha…

The only statement that survives our little examination is about water volume. Water volume is important.  But even there we have a problem.  The volume is in L/ha.  This is useful in some parts of Canada, but not in the west, where producers communicate primarily in US gallons per acre.  And in the west, provincial guidelines have generated this odd hybrid of L/acre, which few people use for spray volume.  But 46.8 to 93.5 L/ha?  How is that level of precision justified? (I know that this is a conversion from 5 and 10 US gpa…so why not just say so?)

A Solution

The problem with having outdated or impractical information on labels is that it creates disrespect.  Since labels are documents enforceable by federal law, applicators want to comply. At this time, they can’t, and probably shouldn’t, if they want to do the job right.

A vision for a good label should be one that respects the needs of the applicator.  Such a label:

  • places the information that applicators need at the top;
  • is updated regularly to reflect modern practice and useful advice;
  • helps a new applicator work out how to apply the product with any equipment;
  • identifies a spray quality that offers good coverage and low drift;
  • makes reference to research that supports variations in the application guidelines;
  • is available electronically, readable on a mobile device, i.e., not pdf.

This label would protect the environment and bystanders, and would foster better pesticide performance.

This label is easy to generate.

This label would be read by applicators.

What’s it going to take?


This article created a great deal of discussion. We decided that if we were going to point out issues with the current labelling system, we should also propose a way forward. Read about our Label Summary Sheet proposal.