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Pesticide waste assigned a number

Crop spray specialist says a surprising amount of crop protection chemical goes down the drain, pegging it at 14.3 percent.

WESTERN PRODUCER — A five- to 10-percent spray waste can be a typical loss on some prairie farms. That is a lot of product missing the target, and it’s avoidable on most farms.

Most spray jobs cost about $10 per acre, with some to $25. If we assume a $25 per acre cost, it’s $4,000 to spray that quarter-section. With a 14.3 percent lost, that’s $572.

Tom Wolf says waste numbers can be cut in half or more, and it doesn’t require a revolutionary technological breakthrough or spending money. It’s simply a matter of following protocols of sprayer maintenance and operation, and using existing technology.

The main tools, says Wolf, are a sharp pencil and a willingness to make changes for the better.

Wolf, owner of Agrimetrix Research, is known as the NozzleGuy. His remarks, made at the Crop Connect Conference in Winnipeg held in mid-February, are based on a chapter in his website at

“This exercise suggests that waste from spraying is probably higher than we assumed. If we average the scenarios, there is 10 percent waste. At $200,000 spent on pesticide for a single spraying season, that’s $20,000 worth of product and water that ends up where it doesn’t belong. Beyond the time and money, there can also be environmental consequences depending on how that waste is treated.”

Wolf said the waste occurs at many points during spray applications:

  • Mixing more chemical than is needed and not trusting the flow meter or tank gauge.
  • Not knowing the exact field size.
  • Boom priming before the first swath.
  • Overlapping coverage areas due to terrain or coarse sectional control.
  • Spray drift away from intended target.

Wolf uses a quarter section as an example of where that 14 percent of wasted product might go. Rounded numbers are used to account for different machines and habits of different operators.

His example begins with a clean sprayer and a task of spraying 160 acres before moving on to a new crop and product. The plan is to apply 10 gallons per acre from a 1,200-gallon tank with a 120-foot boom. We need 1,600 gallons of spray mix in total.

During refilling, an accurate measure of the tank contents is important. Without that, we might not be putting the correct amount in each time.

Once in the field, we prime the boom. Up to 50 gallons can be required to push product from the tank to the last nozzle. Only part of that is lost to the ground because boom sections can be shut off as soon as product has reached every nozzle of that section. Wolf assumed a loss of 0.2 gallons per foot of boom, or 1.5 percent.

Spraying itself is relatively straightforward. Swath and sectional control handle the overlaps. Double application can account for as much as five percent of the area to reach non-square parts of the field. This is a bigger factor when outer sections are 10 feet or more.

Air-activated shutoff for individual nozzles reduces section size at a reasonable cost. For those without individual nozzle shutoffs, chemical loss increases because of early boom turn-on prior to leaving the headland to allow the boom to reach operating pressure.

We can expect a two percent product loss to airborne drift with typical nozzles. Most of the spray that moves more than five metres after leaving boom, stays airborne. It won’t return to the ground within the field borders, so it’s a complete loss.

When finishing the job, the pump will draw air before the tank is empty due to sloshing or foaming. A leftover 50 to 60 gallons is common. This example assumes five percent of tank volume remains, in part because operators may overfill to avoid running out early.

We also need to purge spray from the boom at cleanout, consuming approximately 0.4 gallons per foot of boom. This occurs after the field is completely sprayed and is therefore considered waste.

To show how this adds up, Wolf presents five different examples. We’ll look at some cases.

His Sprayers 101 website shows approximate spray mix losses associated with different setups, with the worst case being a 14 percent spray loss.

  • Setup 1 — baseline 14.3 percent loss.
  • Setup 2 — low application volume 22.5 percent loss.
  • Setup 3 — recirculating boom, tank level monitor, low-drift nozzles 5.8 percent loss.
  • Setup 4 — big area between cleaning 7.3 percent loss.
  • Setup 5 — big area, recirculating boom, tank level monitor, low-drift nozzle 2.6 percent loss.

Setup 1 — We spray 160 acres at 10 gallons per acre. Priming the boom with 0.4 gallons per foot, allowing for all associated feed lines, consumes 48 gallons. But only half that volume is wasted. That’s 1.5 percent of the total volume needed for the field. A 64-gallon overlap is another four percent loss.

If you have 60 gallons of leftover mix, it represents another 3.8 percent of the total sprayed amount. Cleaning the boom at a rate of 0.4 gallons per foot, there’s another 48 gallons or three percent loss. If we add a conservative two percent for drift loss, it adds up to 228 gallons of lost spray, for a total 14.3 percent loss. Cash value of that lost mix depends on the cost of the product. For a $25-per-acre treatment, it’s $572 per quarter.


Setup 2 — For operators using lower water volumes the volumetric losses are slightly less, but their proportion is higher because the tank mix is stronger. Now we’re looking at 22.5 percent of the five gallon per acre rate, meaning 180 gallons miss the target. Cash value of your loss is $900.


Setup 3 — We use a recirculating boom that returns the initial prime volume to the tank, eliminating the previous 1.5 percent or three percent waste outlines in setups one and two.

The re-circulating boom allows the mix to pass through the entire length without being sprayed, thus saving waste during priming and allowing waste-free boom rinses. When the sump empties, we introduce some water from the clean water tank to push the last of the mix to the boom. A continuous rinse system makes this easy.

If we upgrade to individual nozzle sectional control, overlap drops to one percent.

We need to know exactly what’s left in the tank, so we invest in an AccuVolume to precisely monitor tank volume, allowing us to make small rate adjustments up or down to maximize the volume of mixed product actually applied to the pass. AccuVolume shows the exact volume left in the tank at any slope position with one gallon resolution. This allows greater accuracy when filling and emptying. Sump waste is now reduced to 12 gallons or 0.8 percent. We still need to dispose of the content of the boom somehow. The recirculating boom offers no saving there.

But if we have installed better low-drift nozzles, our drift can be cut by half, or one percent of the total mix volume. Low-drift nozzles such as the AirMix (Agrotop) SoftDrop can reduce airborne drift by 50 percent to 90 percent. Total volume loss is now just 92 gallons or 5.8 percent.

The last two rows in the table pertain to a larger sprayed area of 1,000 acres before tank cleaning. This doesn’t change the magnitude of the volumetric loss, but does reduce the proportion because we’re priming and cleaning less often. Percent loss is down by a factor of two from the 160-acre example. Loss figures on a 1,000-acre application range from 2.6 percent to 7.3 percent.

Experienced operators might cheat the system a bit by mixing the required pesticide with some extra water to make up for the plumbing waste. Doing so prevents extra pesticide from being consumed, but it doesn’t reduce the inherent inefficiency.


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