Tag: speed

  • Debunking Sprayer Myths

    Debunking Sprayer Myths

    Reproduced from an article written by Angela Lovell for Grainews, 2014

    “The fundamental challenge of spraying is that it’s a compromise game,” said Tom Wolf of Agrimetrix Research and Training. “As operators and advisors we need to always balance the opposite needs of coverage, efficacy and drift.”

    Wolf, in a presentation at the recent Manitoba Agronomists Conference in Winnipeg, sees a trend towards more fungicide use on farms across western Canada and technology that purports to make application more efficient. These trends include wider booms, faster speed capability, complex monitors, auto boom heights and bigger tanks.

    As much as technology is a great thing, it’s still the operator that is the single most important part of any spray operation, so it’s important to make sure that he or she isn’t going out to the field with any conventional beliefs that simply aren’t correct.

    The challenge with spraying is to control pests without harming you neighbour’s crops or the environment and over the years Tom Wolf has developed some pretty good ideas about how to do that and has had to dispel more than one popular myth about spraying.

    Myth # 1: More pressure forces the spray into the canopy.

    “There’s an element of truth to this but it’s forcing spray downward is the least thing that pressure does,” says Wolf. Spray pressure is primarily used to change spray flow rate. If you increase the pressure you will need to travel faster to allow the carrier volume to stay constant, and faster travel speed actually works against canopy penetration. Another important change is that spray quality will become finer with higher pressure. Finally, droplet velocity will initially increase, but even at higher pressure, small droplets still move slowly by the time they reach the canopy. “If you want to force a fine spray into the canopy, the best way to do that is to lower your boom, slow down, and increase the carrier volume,” says Wolf.

    Myth # 2: Higher water volumes lead to run off.

    There are two things that govern run off; droplet size and surface morphology of the leaf surface. “Anyone who says that anything more than 3 gallons/acre runs off the leaf surface is not telling you the whole picture,” says Wolf. “We’ve been unable to induce runoff from up to 200 US gpa in our tests, even using hard-to-wet grasses like green foxtail. Don’t be afraid of water. It’s a very good way of covering the canopies. Water gives you flexibility to use coarser sprays and that allows you to spray when it’s windier.”

    Myth # 3: Spray drift is no issue for fungicides and insecticides

    Aquatic organisms are extremely sensitive to most fungicides and insecticides. We might not see this effect, but it has a definite impact on our environment. It’s important to observe the buffer zones shown on product labels, which can vary depending on the product, the application method and the specific environment.

    Myth # 4: Faster travel speeds save time and boost productivity

    Wolf suggests evaluating this on a field by field basis. At faster speeds you lose control of the spray cloud and the finest droplets will go wherever the wind goes. Other problems with higher speeds are canopy penetration, pattern uniformity and pressure management. If you have an 800 gallon tank with an 80 ft boom and you are going 12 mph at 10 gallons/ac and your fill rate is 50 gallons per minute you are going to do about 84 acres/hour not including turns. If you go faster – 18 mph – you can do 110 acres/hour. But if you increase your fill speed, thereby decreasing the time spent filling you can increase productivity just as much. If you also increase your boom width you also increase productivity. “All I am asking is you don’t just look at travel speed to improve your productivity,” says Wolf.

    Myth # 5: Double nozzles produce more droplets and improve coverage

    “It’s the droplet size and water volume that drives the droplet numbers produced. It doesn’t matter how many nozzles produce this size,” says Wolf. Although some double nozzles produce finer droplets and therefore improve coverage, others actually produce coarse sprays which may decrease coverage. Pay attention to droplet size first – nozzle manufacturers publish spray qualities from their products. You can increase coverage from a single nozzle simply by increasing the spray pressure so yo produce a finer spray.

    Myth # 6: Calm early mornings have the lowest drift risk

    This is one of the biggest myths out there, says Wolf, and it’s all because of a condition called an inversion, which usually occur during clear nights, and which linger into the early morning hours. Under normal sunny daytime conditions, air currents rise, fall and disperse spray clouds rapidly but under inversion conditions they don’t. This can lead to severe drift issues, even significant distances away from the treated field.

    Under sunny daytime conditions, air temperature cools with height and that allows for thermal turbulence to disperse the spray cloud. On clear nights, the temperature increases with height (the opposite temperature profile, therefore called an “inversion”), and this prevents air from mixing. As a result, the spray cloud will not disperse.

    Assume that the atmosphere is inverted on clear summer nights, extending into a few hours after sunrise. Producers should never spray when an inversion is present, and a good indication might be if fog or smoke hangs in the air and not dispersing.

    Myth # 7: A rate controller calibrates the sprayer

    “Even with a $400,000 sprayer, the rate controller still relies on a single flow meter that sits at the back of the sprayer and measures the total flow to the boom. The operator has no idea where that total flow is going,” says Wolf. As a result, there is still no substitute for individual nozzle calibration. There are various new tools on the market to assist with that but they still need to be done individually.

    Myth # 8: If I mess up agronomic decisions, I can correct that with a good spray application

    A spray application has to be on time to be truly effective, says Wolf. In efficacy studies where yeield was measured, spraying herbicides “on time” (=early) produced a yield advantage over spraying just one week later, even with a spray quality that was so coarse that it resulted in relatively poor weed control. “If it’s breezy, use a low drift nozzle. This allows you the opportunity to spray on time,” he adds.

    Myth # 9: Ammonia is a good general purpose tank cleaner

    Ammonia raises pH and some chemicals like sulfonylurea products dissolve better at a higher pH. But if you have an oily emulsifiable concentrate (EC) formulation, either as a product or adjuvant, a soapy cleanout product will be needed. “Liberty exposes poor tank cleanout because the adjuvant in Liberty is such an excellent cleaner,” says Wolf. After use of an oily product, the use of a wetting agent such as AgSurf will assist in removing oily residue and many soap-based commercial cleaners are available.

    Myth # 10: There is an optimal nozzle that does it all

    “Right now a sprayer costs approximately 100,000 times more than the nozzle and the nozzle is still the part that makes you happy or sad,” says Wolf. “If we inverted the investment trend and said ‘let’s build a better atomizer’ there would be an optimal nozzle right now. But although we’ve made progress with low-drift nozzles recently, the industry still looks for inexpensive, simple ways to atmozie sprays.”

    Spray quality is the language that is used when selecting nozzles. All manufacturers publish spray quality charts for their nozzles that also give recommended pressures to produce different spray qualities using a particular nozzle type. Spray qualities are colour coded and generally speaking the hotter (redder) the colour code the more drift-prone (finer) the spray. There are many nozzle choices and designs and typically grassy targets and contact products require nozzles that will produce Medium to Coarse spray quality. For broadleaf targets and systemic products a Coarse to Very Coarse spray quality can be used successfully. Selecting the right nozzle to produce the quality of spray required is important, says Wolf who recommends Coarse as a general purpose spray quality.

  • Increase Sprayer Productivity Without Driving Faster

    Increase Sprayer Productivity Without Driving Faster

    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 built a model 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).  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

  • How Fast Should I Drive My Sprayer?

    How Fast Should I Drive My Sprayer?

    It seems simple: The faster you drive the sprayer, the more area you cover. This makes higher travel speeds a seductive method for improving productivity. Sprayer manufacturers knew this 25 years ago when pull-type sprayers first received bigger, suspended outrigger wheels. Since then they’ve delivered more powerful engines, better hydraulic motors, smoother suspension and cruise control.

    Each of these innovations still required the operator to consider the relationship between travel speed, pressure, nozzle choice and the desired output per acre. But now we have rate controllers, and we don’t have to think about such mundane things anymore… do we? Do we still do a good job if we go faster? What exactly happens when we speed up?

    Before considering the role of the rate controller, you have to decide on an overall target-speed range. Charts, apps, or online tools can help you select nozzles sized to deliver your application volume at a given speed and pressure. This initial travel-speed decision requires an understanding of how spray gets delivered to the target. Let’s start with the spray boom.

    As the boom moves through air, the oncoming air does three things to the spray:

    • It shears the spray, making it a bit finer.
    • It scrubs the smallest droplets from the pattern, leaving them in the wake of the boom.
    • Finally, negative pressure behind the pattern sucks even more fine spray into the sprayer wake.

    Collectively, these create the dreaded “spray plume” that hangs behind the spray boom… and we’ve lost control over it. The faster we move, the greater the proportion of the spray that ends up in the plume. This can be anywhere from one to 15% of the spray. Once formed, that plume moves with the prevailing winds.

    Today’s sprayers have wide booms, and faster speeds often require us to keep these booms higher than we have in the past to prevent impacts. But higher booms reduce our control over the spray’s direction. For example, when spraying vertical targets (e.g. wheat heads) we have begun to employ angled sprays. But droplets lose momentum quickly. The further they are from the target, the more likely they are to slow or even fall vertically before they reach the target. That means that higher booms often negate the benefit of angled sprays.

    Still not convinced of the perils of high speeds? Well, think about the aerodynamics of the sprayer itself. As travel speed increases, the sprayer, the boom, and even the spray pattern itself disrupt the air around it.  Visualize a sprayer in a wind tunnel with smoke tracer lines. The nice pattern created by the boom gets really messy in a turbulent environment. This can cause a loss of deposit uniformity, resulting in a reduction of overall effectiveness.

    So far, we’ve talked about average speeds – choosing to travel eight, 12 or 16 mph overall, and then choosing the nozzle that will suit. Now let’s talk about changes in your travel speed within your target-speed range.

    Operators know that even small travel speed changes can result in large pressure changes.  That’s because travel speed and pressure enjoy a “square-root relationship”. If you double travel speed, your rate controller needs to quadruple the spray pressure to meet the new flow need!

    Even minor changes in speed (to adapt to field conditions) can lead to big fluctuations in pressure, changing average droplet size, and affecting coverage and drift potential. Severe pressure fluctuations are more likely with a faster average travel speed. That’s perhaps why pulse-width modulation, which decouples spray pressure from travel speed and replaces it with a solenoid duty cycle, has a growing role in fast self-propelled sprayers.

    To minimize pressure fluctuations, use the pressure gauge as your speedometer. Have the boom pressure displayed prominently in your sprayer cab, and try to operate at speeds that result in a pressure which is optimal for the job you’re trying to do.

    So, let’s summarize the effects of fast travel speeds.

    Pros:

    • More area covered per hour
    • Better contact with vertical targets (if the booms are kept low)

    Cons:

    • More drift
    • Less uniform deposition
    • Wider pressure fluctuations

    So, how fast is too fast? We won’t draw a line in the sand, but we will emphasize how important it is to consider as much information as you can before deciding on a travel speed. Don’t rely on the rate-controller to think for you – it doesn’t have all the information.