For Basics Category
We often write about how valuable water sensitive paper can be to visualize and assess the coverage we’re getting from a specific application method. A handy reference is this matrix that combines both factors. Print it and use it in the field to compare what your application method is doing to these relative standards. On average, you will want to see deposits similar to those in the middle of the matrix.
Download US units Matrix here (pdf)
Download Metric Matrix here (pdf)
Fungicide use appears to be the fastest growing segment of North American crop protection. Here is some advice on how to get the best bang for the buck.
Boom height and spray quality are both important for single angled sprays or double nozzles. The angle at which a spray leaves a nozzle diminishes quickly as air resistance and gravity exert their influence. If the boom is too high, the initial forward angle will be lost and the spray droplets will actually deposit with gravity and wind. But if the spray is a bit coarser and the boom is low enough, the angle of attack is retained for long enough to make a difference in spray deposition.
Despite these suggestions for making the spray more effective, there is no substitute for an informed decision regarding fungicide use. It’s possible that spraying is unnecessary for a number of reasons, and it’s best to have professional advice help make that call. If you decide to go ahead, ensure that your sprayer is set up to deliver the fungicide to the part of the canopy that needs protection.
Undoubtedly, the number one question we get from operators is: “Which nozzle should I get”? Luckily there’s no simple answer, or we wouldn’t have jobs! The reason it’s not simple is because selecting the “right” nozzle for a sprayer is a process. It can be broken down into two steps:
It’s a big question, so let’s tackle just the first bullet: identifying the right flow rate.
All sprayer nozzles come in standardized (ISO) sizes, and these sizes are usually identified by numbers stamped on the nozzle as well as the colour of the nozzle itself. The nozzle’s key characteristics (i.e. the fan angle and nominal flow rate), are identified in a format that looks like some version of this (Fig. 1):
The 110 refers to the fan angle (110°) and the 04 refers to the flow rate. 04 means 0.4 US gallons of water per minute (gpm) at 40 psi. Each nozzle brand has a slightly different convention, but no matter how the information is presented it ought to be on the nozzle somewhere.
Nozzle colour has an ISO standard across fan-style nozzles, and we have this table to match the nozzle colour to the flow rate:
You’ll note that the nozzle we pictured earlier was “flame red”, matching the 0.4 gpm on the table. So how do we use the table to pick the right size nozzle?
Application rate (i.e. gallons per acre or L/ha) is a function of travel speed, nozzle spacing along the boom, and nozzle flow rate. Traditionally, this has been expressed as the following formula in US units:
This formula is famously represented in nozzle charts found in all sprayer catalogues (Fig 4). Along the left side are nozzle sizes and pressures. Along the top is sprayer speed. The body of the table contains application volume. Pick your speed, and look for your application volume in the columns. If you want to apply five gpa, you need to look for the number 5 (or as close as you can get to it), among these numbers.
The format of the chart can be confusing because it doesn’t follow a modern sprayer operator’s priorities. Usually, an operator decides on an application volume first, and this decision is not very flexible. Travel speed, decided second, has more flexibility.
We’ve therefore re-worked the table to make more sense (Fig. 5). Along the top are common water volumes. The body of the table are travel speeds. Pick a water volume at the top and follow the column underneath this value to find a speed range you’re comfortable with. To the left, the nozzle size and corresponding operating pressures are now visible.
Try to operate at a spray pressure that’s in the middle of the nozzle’s operating range. For an air-induced nozzle, the range is usually from 30 to 90 psi, so the middle is 60 to 70 psi. That should be the target pressure. Look for a nozzle size that delivers this pressure at your expected travel speed.
These columns can be used to work out a nozzle’s travel speed range. If a nozzle can be operated between 30 and 90 psi, for example, the corresponding speeds are listed in the same rows in the volume column.
For example, say you want to apply seven gpa and think that 13 mph would be a good average travel speed.
Move down the seven gpa column, and you’ll encounter a value close to 13 mph five times – the yellow nozzle at 90 psi, the lilac nozzle at 60 psi, the blue nozzle at 40 psi, the dark red at 30 psi, and the red at about 25 psi. Now use the columns to see which of these three best matches your expected travel speed range.
The yellow nozzle would allow between seven and 12.5 mph from 30 and 90 psi, the lilac nozzle nine to 16 mph, the blue nozzle 11 to 19 mph, the dark red 13 to 22 mph, and the red 15 to 26 mph.
The best choice for a typical air-induced tip would be the lilac 025 size, since it would meet the target speed of 13 mph at a perfect 60 psi, about right for nozzles of that size, and allowing some travel speed flex on the slower side.
Some operators try to extend that range, but dropping below 30 psi will likely result in too narrow a pattern, or too coarse a spray quality, so it’s not advised.
Note that the three-fold change in pressure from 30 to 90 psi translates to only a 1.73-fold change in travel speed. That’s due to the square-root nature of the relationship, as illustrated by this formula:
This exercise applies to sprayers with rate controllers that adjust pressure to regulate flow rates. However, if you use pulse-width modulation (e.g. Case AIM Command, Capstan Sharpshooter, Raven Hawkeye, or TeeJet DynaJet) check out this article describing these systems.
There are a number of apps and websites, usually developed by nozzle manufacturers, which provide similar answers. These are also very useful, and all of them rely on the same formulas used in our new, simplified table. You can go here to download a high resolution version, suitable for framing, in both US and metric units.
Nozzle choice can be overwhelming due to the large selection available from many suppliers. But nozzles are the most important part of the sprayer, being responsible for metering the liquid, atomizing it into droplets, and distributing it across the boom. Review this list for what’s available, then follow these general recommendations.
All sprayer manufacturers voluntarily publish the spray quality of their nozzles at various flow rates and operating pressures. This information is available here from their websites, catalogues, or apps. The most popular tips for field sprayers are the air-induced and pre-orifice low-drift style, and these are typically operated between 30 and 90 psi. As a starting point, look for tips that produce a Coarse spray quality at an intermediate pressure of 60 to 70 psi. This seemingly high pressure is normal for air-induction style tips and provides some necessary travel speed range for self-propelled sprayers.
Spray quality is a useful way to manage spray drift and coverage. The coarser your spray, the higher your water volume must be because you must have enough droplets per unit area to hit your target and provide enough droplet density on the leaves. This is most critical for pre-seed burnoff, where weeds are smallest, and where low-volume, very coarse sprays will likely miss weeds entirely. It is also important for contact herbicides (that require high droplet densities) and for grassy weeds, most of which have a hard time retaining very large droplets. Use at least 7 to 10 gpa for in-crop herbicides, 10 to 15 gpa for fungicides. The taller your crop canopy, the more leaves there are to cover and the more water is required.
Even a good nozzle won’t work well at the wrong pressure. Air-induced nozzles and some pre-orifice nozzles require higher pressures to operate properly. The most common reason for performance complaints is when the spray pressure of a low-drift nozzle is too low, resulting in poor spray distribution between nozzles (see next point). If your sprayer cannot produce sufficiently high pressures, you should not be using these nozzles. Use your spray pressure gauge as your speedometer, and aim for pressures in the middle of the nozzle’s recommended operating range. Higher pressures increase drift potential, but less so for pre-orifice and air-induced nozzles. These tables help size your nozzles for your travel speeds.
Whereas finer sprays from conventional nozzles can re-distribute themselves with wind or turbulence, covering up poor patterns, the coarser droplets produced by low-drift sprays will go where they’re pointed. Therefore, there is only one chance to get uniform coverage across the boom. Before spraying, set your sprayer to your lowest expected spray pressure (say 30 psi) and your lowest expected boom height and inspect the spray pattern overlap. For low-drift sprays, try to achieve a nozzle pattern width that is twice your nozzle spacing at the target height. If necessary, adjust your boom height, increase pressure, or select wider angle nozzles. This will ensure that the coarsest droplets at the pattern edge are mixed in with the more abundant, finer droplets found in the middle of a pattern.
