Sprayer math can be intimidating, but the effort gives solid value. When combined with a calibrated sprayer you reap the following benefits:
Determine how much spray mix is required to apply the intended rate.
Estimate how much crop protection product must be ordered for the season.
Populate spray records which allow you to review practices, respond to enquiries and satisfy traceability requirements.
There are many ways to perform sprayer math, and you need only look to local pesticide safety courses, industrial catalogues, and extension resource centres for examples. If you’re already comfortable with your current method, don’t mix and match with others. Sprayer math is a series of related calculations that employ constants to keep the units straight. It’s all or none.
Walkthrough
Let’s start with the classic, US Imperial formula for calculating the sprayer output. We’ll weave in Metric, later. This base formula can be adjusted to allow you to solve for any factor, as long as you’re only missing one piece of information. Turns out your high school teacher was right – you DO need algebra.
GPM = [GPA x MPH x W] ÷ 5,940
In this case, you can determine an output rate (GPM – gallons per minute). You’ll need to know your target volume (GPA – gallons per acre), your average travel speed (MPH – miles per hour) and your nozzle spacing (W – which is width in inches). The number “5,940” is a constant that handles all the unit conversions. If you divide the GPM by the number of nozzles on your sprayer (assuming they are all the same rate), you can hone in on the ideal nozzle size.
But, as we noted earlier, you can do a lot more with sprayer math than just pick the ideal nozzle size. The rest of this article includes examples of both Metric and US Imperial formulae, but watch out for unit conversions. If at any time you don’t see the units you’re looking for, you can consult our unit conversion tool.
Grab your calculator – it’s math time!
Don’t be intimidated. With a little practice, sprayer math gets easier and it’s always worthwhile. The real trick is navigating unit conversions.
Step 1 – How large is the area you need to spray?
Multiply the length of the area you plan to spray times the width. If you are using metres, then divide the product by 10,000, which is the number of m2 in a hectare (ha). For feet and acres, divide by 43,560 which is the number of ft2 in an acre (ac):
Step 2 – How much product is needed to spray the area?
Consult the rate(s) shown on the label. In Canada, rates are often based on planted area (E.g. hectares). In Australia and New Zealand, they may be based on row length (not covered in this article). If you measure your area in acres, you’ll have to convert the rate by multiplying by a constant: 0.4.
Now multiply the area you want to spray (step 1) by the rate (step 2).
Step 3 – How far can you go on a full tank?
You know your sprayer output (determined through calibration) so you divide that into your tank size. Watch your units:
Step 4 – How much pesticide per tank?
Multiply the area that can be sprayed per tank (Step 3) by the pesticide rate (Step 2). Again, watch your units:
Step 5 – How much area is left to spray?
Just subtract what you’ve already sprayed from the total area.
Step 6 – How much pesticide in the last, partially-full tank?
Multiply the area you have left to spray (Step 5) by the pesticide rate (Step 2). Yes, watch your units:
Step 7 – How much spray mix will I need for the partial tank to finish spraying the total area?
Multiply the area you have left to spray (Step 5) by the sprayer output (determined through calibration). Guess what? Watch your units:
Sample problems
Time to test your knowledge. Let’s suppose you want to apply a product rate of 3 L/ha to your blueberries. You calibrate your sprayer and determine your output to be 50 L/ha. Your tank holds 400 L of spray mix. Your planting is 500 m long and 200 m wide.
Q1 – How large is the area you need to spray?
Q2 – How much product is needed to spray the area?
Q3- How much area can be sprayed on one tank?
Q4 – How much product should be added to a full tank?
Q5 – After the tank is empty, how much area is left to spray?
Q6 – How much product to add to the last, partially full tank?
Q7 – How much spray mix will be needed to finish spraying?
Tank mix calculator
You might feel we buried the lead by adding this calculator to the end of the article. It’s important for a sprayer operator to understand the math required to interpret labels and calculate tank mixes, so hopefully you read and understood the process before you got here. And now that you have, this is a very helpful tool. Try it online, or download a standalone version.
Notable exceptions
Certain situations aren’t covered in this article. If you are spraying a greenhouse, the math is different. If you are performing a banded application, the math is different. And, if you’re an airblast operator trying to reconcile why a pesticide label uses planted area rather than canopy volume for its rates, you’re in for some additional reading.
Sprayer manufacturers have all but offloaded the entire responsibility for drift management to the sprayer nozzle. It’s asking too much.
Sprayers have changed a lot over the past 25 years. They have become larger, with more tank capacity, boom width, and, if self-propelled, horsepower. They are more comfortable and ergonomic, with more sophisticated swath control and guidance systems. But every year, a very important deficiency in their design becomes obvious. Drift control.
The changes described above are intended to improve productivity and fight operator fatigue. Today’s sprayer can cover more ground than ever before. But the demand to cover ground, through a combination of growth in farm size and frequency of treatment, has outpaced machine productivity. As a result, operators find themselves ever further in a time deficit, with acres on the to do list and no time to get the work done.
Spray drift remains the single most limiting factor to the safe application of pesticides. Spraying cannot happen when it’s too windy or during inversions because all agricultural nozzles produce fine droplets whose movement in the atmosphere cannot be controlled. This has been an issue since spraying began.
Simply put, pesticides belong in one place only, and that is on the treated swath. Applicators have some tools to make this happen, such as using coarser sprays, lowering the booms, choosing very specific weather conditions, and the like. But when winds are incessant, and crops and pests are quickly growing out of the treatable stages, what is an applicator to do? There is only one thing they can do: lower their standards. Either miss the treatment and suffer the yield loss, or spray in the wind and hope nothing bad happens.
Neither of these options are acceptable.
There isn’t an easy fix. Spraying is a game of tight margins. The spray liquid in the tank must be atomized into droplets that can make their way to the target and provide adequate coverage when they get there. The total liquid volume to achieve that task must also be practical. The global ag industry has determined, over the past 100 years, that about 100 to 200 L/ha, 10 to 20 gallons per acre, is the ballpark amount that allows reasonable work rates with sprays that are just coarse enough to resist displacement in modest winds. If it gets windier and we need even coarser sprays, we need to add more water to maintain an acceptable droplet density on the targets. And of course, the droplets need to stick to those targets, so there is a limit how coarse we can spray.
Over the past 20 years, we’ve been asking the low-drift nozzle to do the heavy lifting in drift management, and it has served us well. But with a return to more contact modes of action for resistance management, there’s a need to retain good coverage for product performance.
What ag needs is a drift-reducing technology that is better than the low-drift nozzle. We need a technology that maintains a practical water volume limit and combines this with intermediate spray qualities that generate good pesticide efficacy without allowing drift under windy conditions.
These technologies need to do just one of three things: (a) Protect the driftable droplets from exposure to moving air with a physical barrier, (b) make driftable droplets less drift-prone by increasing their velocity, or (c) eliminate the driftable droplets altogether.
Let’s have a look at some options, and explore the pros and cons.
Shields and Cones. A shroud surrounding the boom was first proposed and built in the 1950s in the UK by Dr. Walter Ripper. Although never commercial, his “Nodrif” boom inspired an entire industry that took hold in western Canada in the 1980s and 1990s. Shrouding worked. In studies conducted at Ag Canada, shrouds produced by Flexi-Coil, Rogers Engineering, AgShield, and Brandt reduced drift by up to 80%. But shrouds disappeared in the 90s, partly because of the advent of tight-folding suspended booms where their physical size posed a problem, but also because of crop contamination from the shrouds and poor nozzle visibility in case of blockages.
The advent of the air-induced low-drift nozzle offered an alternative, but coarseness has been taken to its practical limit.
What about a newly engineered version of shrouds that addresses its shortcomings? Willmar Fabrication has created the Redball Buffer Sprayer, for example. We see hooded sprayers in row crops. But there may be other ideas. The simple device called the PatternMaster introduced by KB Industries a few years back was also a step in that direction. Let’s keep working on this.
Figure 1: Shrouded booms, once common on the prairies and proven effective (Brandt cones, top), are still used on research and turf sprayers (bottom).
Air Assist. Small drops don’t drift just because they’re small. They drift because they have very little kinetic energy, and they get blown off course easily. Speed them up, and that problem is solved. Introducing an air stream at the nozzle can do just that. Furthermore, air assist also enhances canopy penetration, a problem that we currently attempt to address with the addition of more water. Again, this idea is not new. Hardi, once the world’s largest sprayer manufacturer, has had the TwinForce boom available for decades. An inflatable bag is positioned over the boom. Openings along the bottom direct the air down. The operator turns a knob in the cab to control fan speed, and another for forward or backward angle, until the combination is suited to the canopy and the travel speed. The SprayAir, out of Carseland, AB (purchased by Miller but no longer available) was a less elegant version because they chose an air-shear atomizer that sometimes required more air than was prudent. Too much air rebounds off the ground, increasing the drift issue. Their Trident boom, allowing a hydraulic nozzle to be used with air assist, continues to have potential.
Air bag type air assist systems were also available from other manufacturers, but none were ever commercially successful.
Figure 2: Air assisted booms such as this Hardi TwinForce accelerate small droplets, reducing their drift-potential and improving canopy penetration (Source: Hardi Sprayers)
Low Booms. How low can booms go? It depends on the nozzle spacing and fan angle. Horsch claims that with a good boom package, this is an option. They are offering 10” spacing, and with wide fan angles, booms as low as 15” would still provide good overlap. Hands up who will try this at 18 mph. Wingssprayer has an interesting design where the boom rests on backswept plastic sheets, providing a physical barrier and a low height.
Figure 3: Low booms can significantly reduce drift, but their success depends on superior stability and height control (Top, Source: Horsch Sprayers; Bottom, Source: Wingssprayer)
Twin Fluid Atomizer. In this atomizer type, both air and liquid are forced out through the same nozzle. The ratio of air and liquid determines the liquid flow rate and the degree of atomization. First introduced by Cleanacres in the UK as the Airtec, improved by Harry Combellack in Australia over many years, and making a re-appearance with the Dutch manufacturer Agrifac, it’s been one of my favourite atomizers. The small amount of air moving through each nozzle is not enough for serious air-assist, but the idea is good and perhaps it can be improved.
Figure 4: A twin fluid atomizer utilizes air (entering from hose) and liquid (entering from boom) to create a spray whose droplet size and flow rate are adjustable. Air generates some assist to reduce drift.
Electrostatics. Forget about it for drift control. The attractive force is so weak that it only works for very small droplets over short distances. It needs air-assist to work properly. See point #2.
Rotary Atomizer. These are common on aircraft these days, as rotary cages, offering a more consistent droplet size range that eliminates the largest, water-wasting droplets, and curtails many of the smallest droplets produced by hydraulic atomizers. These attributes are powerful and address the fundamental problem: If the small droplets drift, then let’s not produce them. In reality, rotary atomizers are used mainly to produce smaller droplets to save water in the aerial business, not really solving the drift problem. In the 1970s and 80s, the concept was advanced by Micron Corporation, led by Ed Bals and later by his son Tom. Although very successful in forestry and hand-held applications in arid regions where water posed a serious limitation, the transition to boom spraying never happened.
Rotary atomizers are now making a comeback with drone sprayers. Though promising, the flow rate capabilities of spinning disks are lower than those of the cages mounted on crewed aircraft. As a result, the disk may flood, and will no longer produce the desired monodisperse distributions.
Figure 5: Rotary atomizers can eliminate larger droplets and sharply reduced the smallest ones, leaving a more uniform sized distribution (insert). They are used on aircraft to save water, but have not been adopted on ground equipment to control drift.
A new Atomizer. All hydraulic nozzles produce a wide variety of droplet sizes, and that variety has provided robust performance over a wide range of conditions. But it can also be a problem. Even the venerable dicamba nozzles that create Extremely Coarse and Ultra Coarse sprays produce some fines that drift in inversions. The idea put forth by Ed Bals, to eliminate the problematic size ranges, is sound. But the rotary atomizer is hard to implement on a boom sprayer. Can there be an innovation that maintains a simple overall design, produces a narrow, but low-drift droplet size range, and mates it to a bit of air assist to get the spray where it belongs? Absolutely.
Figure 6: Current hydraulic atomizers tend to produce a wide range of droplet sizes. The distribution on the left results in significant drift (droplets <150 µm). The one on the right wastes the larger droplets (droplets >600 µm. The narrower span in the centre distribution avoids these problem areas and delivers the spray in an efficacious portion.
Adjuvants. One of the problems with low-drift nozzles is their tendency to generate some very large droplets. These droplets are not very abundant and therefore don’t contribute to coverage, but they nonetheless consume significant carrier volume. The current generation of oil-based drift-reducing adjuvants (DRAs) have helped reduce the drift-prone size fraction without increasing the largest droplet size fraction as much as low-drift nozzles do. This more surgical approach is welcome. Unfortunately, the drift-reducing effect is not as much as low-drift nozzles alone can achieve. A combination of these two technologies is likely the best way forward.
Figure 7: Effect of DRA on driftable fines (left) and overall volume median diameter (VMD, right) from AIXR11004 tip. Data courtesy Winfield United.
Targetted Sprays. An obvious way to reduce drift is to spray less. With recent developments in camera-driven spot spraying, this is already happening. It’s safe to assume that every percentage not sprayed is an equivalent reduction in drift potential. And with reports of 50 to 90% savings, this will be significant. How these product savings are deployed remains important. Some applicators choose to raise pesticide rates to effect better control, and this of course negates some of the gains. Others are increasing the overall spray volume. This then opens the door to the use of coarser sprays without loss of coverage, enhancing gains.
Figure 8: Spot spraying (Courtesy Croplands)
To create value for farmers you first need to understand farmers’ priorities and problems. Getting the spraying job completed on time often means squeezing the work into ever narrower time frame, between rains, between winds in the afternoons and inversions that same evening, between too much dew and too dry, between too early and too late. I am looking forward to the day when engineering resources are allocated to address these issues better, protecting both the environment and the stress levels on the farm.
Timing trumps most things in crop protection. A great spray applied at the wrong time isn’t nearly as valuable as a mediocre spray at the right time. So how do we improve our ability to get things done at the right time?
Often, we try to win races by driving faster. In our last article, we looked at driving speed and concluded that faster speeds can lead to more drift and less uniform deposition. Driving slower can be viewed as a sort of insurance policy: You may not notice the benefits right away, but on days when that extra bit of performance is required, you’re covered.
So how do you get the job done quickly if you can’t drive faster? To answer, we have to look to other opportunities for boosting productivity.
Recently, we used our and tried to capture all the elements of a normal spray operation that affect timeliness. These were:
travel speed
boom width
tank size
water volume
field length
number of headlands
turning speed
fill time
First, we identified a reasonable base condition. For the sprayer, that was a travel speed of 14 mph, a 90’ boom, an 800 gal tank, a 10 gpa water volume, and a 20 minute fill time. Then, we set up a typical field situation, which was spraying a half-mile run on a quarter with two sprayed headlands and a turning speed of 8 mph. Finally, we changed one factor at a time to determine its relative importance.
Before we discuss the results, let’s make it clear that just because changing some of these factors improves productivity doesn’t mean we’re recommending them! For example, adequate water volume remains an important input that improves coverage and permits the use of low-drift sprays. Larger tanks increase compaction and take more power, and so forth.
Here’s what we found:
All productivity values were expressed as acres per engine hour. For this reason, our numbers will be lower than what a typical sprayer monitor reports, most of which calculate acres per spraying hour.
For the base condition, the sprayer spent 15% of its driving time turning, and 37% of its on-field time stationary (i.e. filling or cleaning). For every hour spent on the field, less than half the time (48%) was spent spraying. This resulted in an average productivity of 82 acres/h.
Increasing the spray speed to 18 mph increased average productivity to 93 acres/h, but it also increased the proportion of time spent turning and loading, resulting in just 40% of the field time spent spraying.
Decreasing the loading time from 20 to 10 minutes reduced the proportion of field time spent stationary to 23%, covering 100 acres/h at 14 mph. Surprisingly, this was the productivity-winner, resuling in 62% of on-field time spraying.
We discovered other powerful productivity factors, and chief among them was boom width. A 33% increase in boom width from 90’ to 120’ gave a productivity boost to 94 acres/h, close to the same result as increasing the travel speed to 18 mph earlier. Similar side effects occurred: more time turning, and a greater proportion of time filling, as we saw with faster travel speeds.
Boom width seems to have some room for growth. Many smaller European counties use wider booms than we do in North America, for example. With gps guidance and large fields, we have excellent conditions for their implementation.
Two other factors that had similar effects to fill time were water volume and tank size. Less water and larger tanks increased productivity by decreasing the fill frequency, with effects similar in magnitude to speeding up the fill time. Decreasing the water volume from 10 to 5 gpa increased productivity to 100 acres/h by decreasing the proportion of time the sprayer was stopped from 37% to 23%. Increasing from an 800 to a 1,200 gallon tank increased productivity to 94 acres/h, again by decreasing the proportion of time spent filling to 28%.
Taken together, a sprayer with a 120’ boom, a 1,200 gal tank, applying 10 gpa and filling in 10 min had an average productivity of 132 acres/h. And this was achieved without driving faster than 14 mph. If you can string two quarters together and drive a whole mile before turning, that number rises to 145 acres/h, a surprisingly large 13 acres/h gain.
The perspective of minimizing downtime extends to other tasks, too:
Be more prepared for the job by reviewing the product label in advance, noting the correct mixing order.
Keep extra nozzles, clamps, and nozzle bodies in the cab.
Don’t clean plugged nozzles, replace them.
Use low-drift nozzles so a small increase in wind doesn’t shut you down.
Ensure all the products needed are on the tender truck (e.g. pesticide, adjuvant, tank cleaner, anti-foamer, etc.).
Consider switching to 3” plumbing (pump rates of 300 – 400 gpm are possible).
Make sure your inductor won’t be the limiting factor. For example, product pumps can be awfully slow when the product is cold. It might be worthwhile to explore a venturi system.
Speeding up the fill process is a good idea, but be careful with certain products. Dry materials such as the sulfonyl ureas (e.g. Refine, Express SG, etc.) and some fungicides (e.g. Astound, etc.) require time to hydrate in water so they mix properly. Some operators pre-hydrate these in a smaller tank, while others get an extra tank to pre-mix whole loads and simply transfer them over.
Also think about the time spent cleaning the sprayer. Thoroughness is important, but perhaps there are efficiencies to be gained there as well, like never letting a sprayer sit after spraying. We’ve written about continuous rinsing, for example, to improve cleaning speed and effectiveness.
So, the quicker we can spray, while ensuring a quality job, the more effective our crop protection practices will be. We encourage you to use our to determine your best configuration.
Got a productivity tips to share? Let us know! And remember: In spraying, the race is won in the pits.
Factor
Base
Drive Faster
Fill Faster
Spray Wider
Less Water
Bigger Tank
New Sprayer
Travel Speed
14 mph
18 mph
14 mph
14 mph
14 mph
14 mph
14 mph
Fill time
20 min
20 min
10 min
20 min
20 min
20 min
10 min
Boom Width
90 ft
90 ft
90 ft
120 ft
90 ft
90 ft
120 ft
Water Volume
10 gpa
10 gpa
10 gpa
10 gpa
5 gpa
10 gpa
10 gpa
Tank Size
800 gal
800 gal
800 gal
800 gal
800 gal
1200 gal
1200 gal
Field Length
0.5 mile
0.5 mile
0.5 mile
0.5 mile
0.5 mile
0.5 mile
0.5 mile
Time Turning
15%
19%
15%
20%
15%
15%
20%
Time Loading
37%
42%
23%
42%
23%
28%
19%
Time Spraying
48%
39%
62%
38%
62%
57%
61%
Acres/h
82
93
100
94
100
94
132
To work with the productivity calculator, click here.
Crop spraying is one of the most important and highly skilled jobs undertaken on any arable farm, but it is facing increased public scrutiny. This is why it is vital that the kit you use as a means to apply pesticide to crops is in prime working order and is set up correctly to deliver the product safely and accurately to its target. Optimum sprayer set up will help to maximize the efficacy of applied products, reduce spray drift and keep machinery in good condition.
For this best practice guide to sprayer set up, Farmers Weekly teamed up with former Farm Sprayer Operator of the Year Iain Robertson. Mr. Robertson is assistant arable farm manager at David Foot Ltd, a 2,200ha mixed farm south of Dorchester in Dorset, growing wheat, barley, beans, oilseed rape and maize as forage for the farm’s three dairy herds. The machine used for this guide is a Bateman RB26 self-propelled sprayer and while most of these checks and tests are universally applicable to all sprayers, it is also important to refer to the handbook of the manufacturer of your specific machine.
Watch the video tutorial with Mr. Robertson and then see the step-by-step guide below for more detail.
Pre Start Checks
Before firing up the engine, the first thing to do is your pre-start checks – that means checking your machine’s vital fluids like fuel, hydraulic oil, hydrostatic oil, engine oil and coolant levels. If yours is a self-propelled sprayer, chances are you’ll need to get up on to the back of the machine to check some of these.
“While I’m up on the back of the sprayer I also have a quick look in the top of the tank to make sure that it is nice and clean and the tank rinse nozzles have worked properly – cleanliness is next to godliness,” says Mr. Robertson. Next, move on to the tires. Use a pressure gauge to check all tires are at the correct pressure and refer to the manufacturer’s guidelines. If you’ve got a trailed sprayer, don’t forget to check the tractor tire pressures as well.
Aim for tires to be run at the lowest pressure recommended for the load to be carried. This will help with boom height and stability and also helps tires act like a shock absorber to ride out bumps. If using a trailed sprayer, use a spirit level to ensure that the drawbar is level. Mr. Robertson says he tries to work around the machine in a methodical, clockwise manner to ensure that he doesn’t miss anything.
Coming to the pumps, check that they have got enough oil, check that any tool boxes have enough spare parts and any equipment needed and make sure you are carrying a spill kit with absorbent granules and a spade in case the worst happens and there is a spillage. Make sure all parts are lubricated daily and that any grease nipples are cleaned before and after use to avoid them collecting dirt and blocking.
Check all hydraulic hoses, spray lines and air lines for any signs of wear that could result in problems while operating.
It’s best to run the sprayer at a minimum of 5 bar to check for leaks. Also check the spray tank is fixed down securely, all straps and bolts are tight.
Boom checks
Once opened out, check the boom has good movement in the x- and y-axis. All machines are different so check with your manufacturer as to how the boom is set up. Mr Robertson’s Bateman has tie rods and stock bots that can be adjusted to set the boom up to ride well.
Check the tie rod nearest the back of the machine is slightly loose when moving and that the front rod is tight. Next, check for up and down movement by gently pushing the boom down by about 50cm and letting go. The boom should return to the central position without too much bouncing around.
“We want a little bit of movement but not excessive so that you can ride over the bumps as you go along without over- and under-dosing the crop,” says Mr. Robertson. Boom height is one of the most critical factors when spraying and the ideal height is 50cm above the crop. One of the easiest ways to work this out is by using a cable tie that is cut off at the correct length to use a visual aid from the sprayer cab.
Don’t forget to measure from the tip of the nozzle to the crop, not the spray line.
Good sprayer cleanliness is important, so make sure the system is rinsed through at the end of each day with clean water to make sure there’s no residue left in the boom. If your machine’s boom doesn’t have recirculation, remember to take the end caps off occasionally and flush out the whole boom.
Nozzle checks
Check that the nozzles are aligned both vertically and horizontally, according to the NSTS guidelines. Loosen clamps to adjust any nozzles that need realignment.
Check the nozzle output at least twice a year by running the sprayer with clean water at 3 bar pressure. Time the output of each nozzle for 30 seconds. If nozzles have been used previously, it’s best to check their output against that of a new pair. Mr Robertson advises using a measuring cylinder rather than a jug to measure the flow rate as a jug is less accurate “because you get a bigger variation over the wider surface area”.
With an 03 nozzle running for one minute at 3 bar pressure, the output should be 1.2 litres/minute as a rule of thumb but refer to the nozzle manufacturer’s output chart for the expected flow rate. “An easy way to remember this is: at 3 bar your nozzle size multiplied by four will give you your target litres/minute output. It works for all nozzle sizes.” If the output varies more than 4% of the average, or if the spray pattern visually doesn’t look correct, you need to change the nozzle set.
After checking the output, cross-reference this figure with the rate controller – you may need to adjust the flow figures to ensure that the two correlate. If a nozzle becomes blocked while spraying, Mr. Robertson says he will swap it for a new one and then clean it later using a toothbrush or airline. Never blow through a nozzle with your mouth.
Nozzle choice
The choice of nozzle is highly dependent on the sort of job you’re doing. “Timing is crucial but using the right nozzle at the right time will make the job so much easier, cut drift and mean that you’re getting more of the product where you want it to go. If you aim at it you will hit it,” says Mr. Robertson.
His nozzle of choice is an 03 size and he prefers to use the Defy 3D nozzle alternated forwards and backwards across the boom for pre-emergence work and T0 applications as well as the T3 ear spray. “In less than optimum conditions I may prefer to use the Amistar/Guardian Air, a fine induction nozzle. I would use this at T1 and T2 and also in sub-optimum conditions.” This nozzle has a 3-star Local Environmental Risk Assessment for Pesticides (LERAP) rating and is 75% drift reducing.
A water volume of 100 litres/ha is a good rate for spring fungicide application. It provides enough coverage for good disease control and allows maximum efficiency from the sprayer.
Forward speed
The third and final part of reducing spray drift is forward speed. Depending on nozzle size and water volume, aim to travel at 12kph.
Mr Robertson says he finds that this speed gives a good overall output and means you don’t get shadowing or turbulence behind the machine.
Tips and tricks
One of the biggest risk of contamination is at fill up. “A fantastic, cheap trick that I learned through Farm Sprayer Operator of the Year is to take a 200 litre plastic drum and cut it in half to create two drip trays to catch any spillages under the induction hopper and the tank overfill.” This eliminates point source contamination, he says.
“Finally, there’s a plethora of information out there on the internet, loads of good apps to download. The technology is there to help us do the best job possible and make our job as safe as possible.”
A Veteran Applicator’s Questions about Pesticide Handling
Time and again, after years of working with dozens of different chemicals, I would wonder to myself “How dangerous is this chemical?”, “Is glyphosate as safe as they say it is?”, “How do I find out what type of safety gear I need while handling this chemical?”
Beyond the agrichemical dealer, ag. consultants, and university or government ag. extension specialists, a quick internet search reveals many sources of pesticide information. Collectively they identify the active ingredient(s) in formulated products, they detail which pests are best controlled by the pesticide, and they provide instruction for application. But it’s more difficult to find consistent, practical information about safe pesticide handling. Sometimes it’s excessive to the point of being impractical (try finding actual “chemical proof” gloves), and sometimes it’s minimal and vague – it depends where you look. No matter the level of precaution, pesticide safety is time consuming and involves some fussing, but it is the hallmark of responsible pesticide use. Just as we ensure that we are applying “safe rates” when spraying chemicals, we must also ensure we are respecting our own well-being while handling chemicals.
In Canada, the Pesticide Regulatory Directorate (PRD) is charged with protecting human health and safety by monitoring pesticides that are sold in this country. According to the Federal Pest Control Products Act all pesticides sold in Canada must be registered with the PRD. There’s a very nice overview of how that process works here. It is during this registration process that pesticide handling precautions are identified for the label. Further classification may take place under provincial acts.
All pesticides are designed to disrupt, repel, control or kill living organisms, but when it comes to safe handling, insecticides receive the most attention. This is because herbicides and fungicides target biochemical pathways that only exist in plants or fungi. However, most pesticides can be hazardous if they are not handled correctly. The handling precautions that appear on the label are based on five factors.
Five factors that affect handling precautions:
1. Pesticide Family
This factor is the broadest way to categorize potential risk to the handler. Generally, herbicides and fungicides are considered safer than insecticides, but there are notable exceptions. Do not rely solely on the pesticide family when making decisions on pesticide handling.
2. Pesticide Mode of Action
The mode of action gives further detail into how a pesticide should be handled. Modes of action that inhibit biochemical pathways that exist in the target pest, but not in mammals (people, in particular), have lower acute toxicities. Examples include herbicides that inhibit enzymes involved in amino acid synthesis or in photosynthesis – these enzymes do not exist in mammals. However, once again, there are always exceptions. Do not rely solely on mode of action when making decisions on pesticide handling.
3. Pesticide Formulation & Route of Entry
Pesticide formulation affects how a product can potentially be absorbed into the body. Emulsifiable Concentrates (ECs), for example, have higher rates of absorption than solutions or dry products. When it comes to the route of entry, dermal contact is considered safer than inhalation or ingestion. However, not all parts of your skin are created equal, and the point of dermal contact on the body matters a great deal.
4. Pesticide Toxicity
Taken collectively, the first three factors form the overall toxicity of the pesticide. The level of toxicity cannot be predicted – it has to be tested. The LD50 (defined below) values that are reported for a pesticide come from standardized experiments such as animal feeding. Although the chosen species (usually white rats for mammalian endpoints) are known to be similar to humans in their response, there is still the possibility of error. Nevertheless, toxicity forms an important basis for establishing handling precautions.
5. Operator Exposure
People handle toxic substances every day. Household bleach, for example is surprisingly toxic, and yet it can be readily found on kitchen shelves in many homes. The risk of being harmed by a toxic product can only be determined by the likelihood of exposure. While it is possible someone might accidentally consume a hazardous dose of bleach, it’s improbable. Exposure does not just refer to a single exposure to a substance – repeated exposures to small doses of a toxic substance can have a cumulative effect. The goal when handling any pesticide is to minimize exposure, but it becomes even more critical when that pesticide is highly toxic. Together, exposure and toxicity form the basis for risk.
Risk = Hazard x Exposure
Studies have shown that exposure is greatest for handlers of agricultural pesticides during the mixing and loading phase of spraying. During this phase, the risk to the handler may be increased due to:
physical stress
the denial of risk
a negative opinion of personal protective equipment (PPE)
The main method of pesticide exposure is dermal, and many of the surfaces on a piece of equipment are already contaminated.
Health effects of pesticides: Acute and Chronic
Acute: short term
High exposure, resulting in immediate reaction due to a high dosage of pesticide exposure. The severity depends on the toxicity of the molecule and entry into the body (dermal, oral, eyes, etc.). The most common acute reaction is skin irritation, although in certain cases respiratory, digestive, and neurological systems may be affected. Organophosphate (e.g. Lorsban, Malathion) and carbamate (e.g. Sevin, Lannate) insecticides inhibit the cholinesterase enzyme, which is found in humans and affects nerve function. Frequent users of these insecticides undergo regular blood tests to ensure their levels are normal.
Chronic: long term
Chronic affects are more prolonged as they are usually due to lower doses of pesticide exposure over a longer period of time. Although some rare cancers and disruption of the reproductive system have shown to be related to this type of exposure, when the general population and farming population have been compared in studies, the farming population has shown an under-representation in the majority of cancers. In the cases were reproductive malfunctions were observed, a different cause of the malfunction, such as genetic offset, was most often observed in these situations. However, cancer types such as skin cancer and brain cancer were overrepresented in the farming community. A study in France has shown that the onset of neurological disorders in Agriculture communities shows a strong connection between Parkinson’s disease and exposure to pesticides.
Label Information
The majority of information needed to safely handle pesticides is found on the label. Pesticide labels are legal documents, meaning they can be enforced by the federal government. The problem is that most sprayer operators rarely look at the label as they are not very reader friendly and easy to skim through. Most pesticide boxes even have the recommended rate, or acres/case on the side of the box now, so there is even less reason to look at the label.
LD50– the dose of pesticide in mg per kg of the test animals body weight that is lethal to 50 percent of the group of test animals. For example, if the pesticide has an acute oral LD50 value of 1000 mg/kg, and the test animals each weigh 1 kg, then 50 percent of the animals would die if they each ate 1000 mg of pesticide at once. A 100 kg animal would need to ingest 100,000 mg (100 g) of the pesticide for the same effect. LD50 is often expressed by the route of entry – dermal, inhalation, acute oral (ingestion) are the main examples.
Degree of Risk and Hazard Symbols
Two Factors that Determine the Appropriate Level of PPE
The Hazard Rating (above) incorporates the minimum protection generally required for a substance with the rating.
The Label Recommendations will usually give the additional specific protective clothing and equipment needs for an applicator.
Degree of Exposure
This increases as the length of each pesticide application increases. As the number of pesticide applications increases, the time between exposures decreases. If an operator becomes exposed to spray, dust or fumes the degree of exposure increases. Essentially, more protective wear is needed as the degree of exposure becomes greater.
Knowledge
This encompasses all of the above information. In order for a pesticide applicator to avoid injury or the chances of adverse effects on the body, a pesticide applicator must be knowledgeable about pesticides. It can be overwhelming for an applicator to sort through all of the information on the label or on-line regarding pesticides. So much so, that most often applicators avoid the information altogether. Ongoing training and learning will ensure that they are effective in their work. Many aspects of pest control change continuously, as new studies are conducted on the effects of pesticide exposure.
A Safety Data Sheet (SDS) is available for each pesticides registered, and these are usually linked on manufacturers’ websites. It can be eye-opening what types of toxicity tests are done, and what the results are.
Denial that pesticides can potentially cause harm is also a major flaw in the behaviour of applicators. Maintaining a safe work environment and practicing personal safety will reduce the chances of an applicator experiencing serious injury throughout their farming career.
Unknowns
There is very little certainty in toxicology. For one, most testing is done using acute oral and dermal dosing. Basically, toxicologists expose test animals to the neat active ingredient and watch what happens. There is a lot of missing information – what about formulant like solvents, and surfactants? What about synergies in tank mixes? Some, but not all of these, undergo testing. We also have much less information on chronic (long-term) effects, and can only simulate these in quasi long-range tests. In addition, toxicological methodologies and statistical approaches can vary, and we should not be surprised that some reports disagree, and that there are outright conflicts between toxicologists and epidemiologists (scientists that study patterns of health in populations). Regulators are aware of these shortcomings and often use safety factors to account for them. But those of us that use these products regularly, the message is simple: be cautious, and protect yourself.
Avoid Cross-Contamination
Disposable nitrile gloves are the product of choice for handling pesticides. But one of the most common problems with the use of gloves is cross-contamination. You’re handling product with your gloves on, touching containers, hoses, valves, and couplers. When you’re done, you climb back into the cab where you take off your gloves. Later, someone climbs up into the cab to talk to you, using the railing and operating the door handle without gloves. Guess what’s on their hands? Even later, you put away the hose without gloves and return to the sprayer. Now it’s on the steering wheel and all the levers. There are a few solutions:
Double-glove so you can take the dirty outside glove off and still be protected.
Wipe down surfaces that you might touch with gloved or bare hands daily.
If using non-disposable gloves, avoid lined gloves and rinse the insides out daily.
Learn More
If you would like to learn more about pesticide safety, or to obtain pesticide application training, the Pesticide Applicator License can be obtained from the Ministry of Agriculture. This course offers in depth, valuable safety information for applicators, as well as general knowledge for pesticide applicators. The Pesticide Regulatory Directorate provides workers, employers, and the general public with a wide range of pesticide information. The PRD can be contacted from anywhere in Canada toll free at: 1-800-267-6315
Download this Quick Reference Guide for commonly used herbicides. Print, laminate and post it at the fill station or pesticide storage area for easy reference. Also, grab a copy of Health Canada’s “Stay Safe when using Pesticides” factsheet.
