A set of new sprayer nozzles can cost $500 to $1,000, while a new sprayer can clock in at $400,000. “But almost the entire probability of application success depends on the nozzle,” says Tom Wolf, co-owner of Agrimetrix Research and Training in Saskatoon.
He’s not saying that farmers shouldn’t invest in a new sprayer if they really need one. But when it comes to your investment in fungicides, understanding how to get the best performance out of today’s nozzles is where the bigger return lies.
Wolf is a specialist in spray technology and has done extensive work in herbicide application efficacy. As he turns his attention to fungicide application, he says the questions are the same, such as what is the optimal droplet size, angle of spray, water volumes, boom height and travel speed. But the challenge is quite different.
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“Weeds are small and on the ground,” says Wolf of the early-season spray timing. “There’s not much canopy, so there’s not much of a problem reaching weeds. But with fungicides, the canopy can be up to four or five feet high, and disease can occur anywhere within it.” Not to mention that it also occurs on variously oriented plant parts — stem, leaf or head — which presents its own challenges.
The trouble is that while farmers are increasing their use of fungicides, the best practice knowledge pool for successful application looks more like a puddle.
So, with funding from the WGRF and Saskatchewan’s Agriculture Development Fund, Wolf, along with colleagues Randy Kutcher and Bruce Gossen, has designed a three-year study to identify the key variables farmers need to focus on to get the best fungicide spray coverage and, by extension, the best disease control out of the spray equipment they have now, or will buy in the future. (Funding support is also being provided from nozzle manufacturers Wilger Industries, TeeJet Hypro and Greenleaf Technologies.)
Straws tell the tale
The first order of business for Wolf and his team was to test various nozzle types and application practices in controlled lab conditions to see how adjusting various factors might affect canopy penetration and spray deposition.
“We designed the experiment to isolate particular application factors, like travel speeds, water volumes, spray pressures and nozzle type, and configurations, such as leading and trailing fan positions,” says Wolf.
The experiments were conducted over the summer and fall of 2014 in a track room capable of carrying a multi-nozzle boom at speeds up to 16 km/h. Wolf’s team created broadleaf and grass crop canopies, then placed plastic drinking straws into the top, middle and bottom third of each canopy to act as spray deposition targets.
“The straws are the approximate dimensions of field targets, like a flag leaf or wheat head,” says Wolf, adding that they were positioned horizontally and vertically so they would mimic an actual field target even more closely. Drinking straw targets were also set just outside the plant canopies as a check.
Researchers then sprayed the canopies, using various nozzle configurations and application techniques, with a liquid that contained a fluorescent tracer dye and a non-ionic surfactant. “We introduced some variability by slightly altering the location of the straws, such as making sure they weren’t under the same leaf for every test,” says Wolf.
After each pass, the straws were individually washed in an ethanol solution to remove all spray liquid for measurement. The amount of spray deposited on each in-canopy straw was expressed as a percentage of what was deposited on the out-of-canopy straw checks.
Surprises and confirmations
Results are preliminary, but a few things already stand out to Wolf. “A big belief is that spray pressure forces droplets further into the canopy,” he says. “It turns out that spray pressure is not that important a factor.” This is mainly because the higher the pressure, the finer the droplets and the less able they are to push through the air pressure they encounter when they leave the nozzle.
Similarly, you’d think that narrower nozzle spacings and slower travel speeds would improve a spray application, but Wolf’s lab study calls both ideas into question. He found that canopy penetration and spray deposition were not improved when nozzles were 25 cm apart, compared to 50 cm apart. “Travel speed has a role to play,” says Wolf, but slow isn’t always better. “With fusarium head blight, we found that a faster speed with the right spray angle was more effective.”
Other intuitive theories were confirmed by the study, however. For example, Wolf found that higher water volumes tended to increase product penetration into broadleaf canopies, but didn’t make much of a difference in cereal canopies, and backward-angled sprays were better at getting into the mid-canopy of cereal crops than forward-angled ones.
The lab experiments also show that the benefit of forward-angled sprays is pretty specific to vertical targets at the top of a cereal canopy, and that the twin-fan nozzles that produce this kind of spray work best at low boom heights. “If you’re going to be using twin angle fan nozzles for fusarium head blight, make sure the spray is coarse and the booms are low,” says Wolf. “If the boom is 30 inches or more above the canopy, it’s not worth going with angled nozzles.
“If you want to be really precise with the spray angle, you have to be even lower,” Wolf says, noting the study showed that spray retention on the vertical straws improved by about 30 per cent when the boom was placed 20 inches above the canopy, compared to 30 inches. “You’d see further improvements at 15 inches, but there comes a point when you just can’t go any lower.”
Practical advice for the field
The lab work is interesting but is it translatable to the field? That’s what Wolf is about to find out via test on actual farms this summer.
“We are dealing with collaborators who will conduct commercial-scale trials,” Wolf says. “It’ll be a real reality check to see if what we see in the lab will work in the field.”
The bugaboo of successful fungicide application is that so many variables are in play. Wolf understands that and says that even though this research aims to examine a multitude of factors, his goal by the end of the study is to identify the ones that can really make a difference to a grower’s success or failure.
“The demands on a farmer’s resources are huge,” Wolf says. “I would like to keep it as simple as I reasonably can — we’re going to evaluate 10 to 20 variables, but we may recommend only two or three that really count.”
Wolf says the goal of the research is much bigger than coming up with a narrow list of dos and don’ts for fungicide application. Because sprayer and nozzle technology is constantly changing, he thinks it’s more useful if farmers understand the principles of good canopy penetration and spray deposition so that they can apply that knowledge now and in future too.
“As scientists, we seek principles as opposed to direct answers,” says Wolf. “We want to know how things work, not just what things work best. A much better service is provided if, when an untested product comes out, we can predict what it is likely to do.
“Farmers have a huge investment in maintaining yield and quality,” Wolf says. “I want to give them as much information as I can to help them maximize that potential.”
WGRF is a farmer-funded and directed non-profit organization investing in agricultural research that benefits producers in Western Canada. For over 30 years the WGRF board has given producers a voice in agricultural research funding decisions. WGRF manages an Endowment Fund and the wheat and barley variety development checkoff funds, investing over $14 million annually into variety development and field crop research. WGRF brings the research spending power of all farmers in Western Canada together, maximizing the returns they see from crop research.
