Author: Tom Wolf

  • We Need Better Drift Control Technologies

    We Need Better Drift Control Technologies

    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.

  • 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 used our productivity app 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

  • Cleaning Your Sprayer

    Cleaning Your Sprayer

    We all know the importance of cleaning out a sprayer. It protects a sensitive crop. It protects people working with the sprayer. It protects the sprayer and its components. But cleaning the sprayer is a pain. Here are some tips to make it easier.

    Some herbicide label instructions are cumbersome, requiring many flushes with full tanks of water. Many applicators look for shortcuts and hope they get away with it. It doesn’t have to be guesswork. The following is a checklist that may help.

    Be Prepared

    A few supplies can help ensure a clean sprayer tank.

    • A defoaming agent saves water and time
    • A cleaning agent (commercial products, or simple household ammonia) is useful, and recommended, for Group 2 products except the imidazolinones.
    • A supply of clean water, preferably with its own pump, and a pressurized spray hose helps clean the sprayer inside and out.
    • A wash-down nozzle (whose flow requirements can be met by the clean water pump) can automate the tank wash-down.
    • A bucket and brush for rinsing screens is very useful.

    Products to Watch:

    The products most frequently implicated in sprayer contamination are two members of the Group 2 modes of action: the sulfonyl ureas (e.g., thifensulfuron (Refine) and tribenuron (Express)), and the triazolopyrimidines (e.g., florasulam (Frontline, PrePass) and pyroxsulam (Simplicity)). Since these herbicides dissolve better at higher pH, proper cleanout usually requires ammonia, a weak base that raises the solution pH. The third member of Group 2 products, the imidazolinones (imazethapyr (Pursuit), imazamox (Solo, Odyssey), imazamethabenz (Assert), imazamox (Ares,  Adrenalin, Altitude or Viper)), tend not be implicated in as many residue issues, and don’t require ammonia for cleanout.

    Be Prompt and Thorough

    Remove pesticide from mixing and spray equipment immediately after spraying – it makes the job easier. The main areas of concern are the tank wall, sump, plumbing (including boom ends), and filters. First, spray the tank completely empty while still in the field. It’s sometimes OK to cover previously sprayed areas – all herbicides must be crop-safe at twice the label rate to be registered by the PMRA. Take care with residual products that may create problems down the road. Reduce the rate or choose a fallow field to be certain. Second, add 10 x the sump’s remnant of clean water, circulate, ensuring agitation is on, and spray it out in the field as well. Repeat. These two rinsing steps will take care of the majority of the cleaning and won’t take very long. The less remaining volume there is in your tank after the pump draws air, the less water is needed to dilute this remainder to an acceptable concentration. Having a clean water tank on the sprayer and a wash-down nozzle makes this job easier.

    Visual Inspection

    Herbicide residue may precipitate out of solution in some parts of the sprayer or plumbing. A thorough visual inspection can identify these problem areas and ensure that they are cleaned properly.

    Tank Wall

    Removal of residues from tank walls is best accomplished with a direct, pressurized spray. Make sure all parts of the wall have been in contact with clean water. Use a wash-down nozzle if it provides complete and vigorous coverage of the interior tank surface.

    Sump

    Empty the sump as completely as possible by spraying it out. Any spray liquid or herbicide concentrate remaining in the sump area will be re-circulated in the sprayer. The only way to remove any remaining herbicide is through dilution by repeatedly adding water, and leaving as small a remainder as possible.

    Plumbing and Boom

    Plumbing can be a significant reservoir of herbicide residue. Removal from plumbing can be achieved by pumping clean water through the boom while ensuring that all return and agitation lines also receive clean water and all residue is flushed out. This may require opening and closing various valves several times, and repeating the process with new batches of clean water. Boom ends can extend up to 6” beyond the last nozzle at each end of each boom section. These ends must be flushed to removed trapped residue. A useful product that does this automatically is the Pentair Hypro Express Nozzle Body End Cap, or better yet, consider recirculating booms.

    Dilution

    The most effective use of a volume of rinse water is to divide it equally across several repeat washes. Assuming a 10 gallon sump remainder, three washes with 30 gal each are as effective as two washes with 70 gallons each, and equal a single 600 gal wash.

    It’s even more efficient to use a separate clean water pump, introducing clean water as the rinsate is sprayed out. This saves water and time, and results in even more dilution.

    Filters

    Nozzle screens and in-line filters can be a significant reservoir for undiluted or undissolved herbicide and are one of the most overlooked parts of sprayer decontamination. Remove all filters and nozzle screens and thoroughly clean these with fresh water. Run clean water through plumbing leading to the screens.

    Nozzle Bodies

    Nozzle bodies can harbour herbicide mixture. When cleaning a spray boom, rotate through all nozzles in a multiple body to ensure clean water reaches all parts of these assemblies. Remove screens that may have been used with herbicide.

    Tank Cleaning Adjuvants

    Adjuvants such as ammonia can assist the tank decontamination process, especially with sulfonyl urea and triazolopyrimidine-containing products. Ammonia does not neutralize herbicides, but it does raise the pH of the cleaning solution which helps sulfonyl urea herbicides dissolve. When decontaminating after an oily (EC) formulation, the use of a wetting agent such as AgSurf will assist in removing oily residue that may trap SU herbicide on tank and hose material. Commercial tank cleaning products that contain ingredients for removing persistent deposits are available.

    Tank and Boom Material

    Both plastic and stainless steel are common tank and wet boom materials, and both can be cleaned using the above procedures.  However, stainless steel is easier to clean, and this means that less time may be required. Consider the choice of materials a productivity factor in your next purchase or upgrade decision.

    Rinsate Disposal

    Always spray out the tank in the field. Do not drain the tank while stationary unless you are certain it is free of pesticide and that you are away from sensitive areas and waterways. Consider a continuous rinse system. Consider building a biobed for safe disposal of dilute pesticide waste.

    Sprayer cleanout will probably never be the easiest job on the farm. But looking at it in a smarter way can prevent frustration and save time.

  • Spray Water pH

    Spray Water pH

    The scuttlebut on coffee row is that acidifying a spray mixture improves its efficacy. There are also claims that pesticides break down in the sprayer tank if the pH is too high.

    But it’s not that simple. Low pH has a strong impact on pesticide solubility, and that means mixing and cleanout are affected. Acidifying the mixture can have profound negative effects for many products.

    It’s important to know what you’re doing.

    What is pH?

    pH is defined as the negative log of the molar concentration of hydrogen ions in a water-based solution. The more abundant the hydrogen, the lower the pH. It’s a log scale, so every unit of pH refers to a 10-fold change in the concentration of hydrogen ions.

    Both very low (acidic) or very high (basic) pH can be caustic. But having a low or high pH doesn’t mean it will burn your skin or clothes right away, it might just be a bit unpleasant. But at the extreme ends, protection is needed.

    Why is pH Important in Spray Mixtures?

    In spraying, the main effect of pH is on the pesticide’s solubility. Solubility matters when mixing and becomes important during cleanout as well.

    A minor effect on pH, at least for herbicides, is on chemical breakdown, usually through hydrolysis, when the pH is too high. The effect on breakdown is rarely meaningful during any given spray day, but may play a role if a spray mix is stored overnight or longer.

    The Basics: Strong vs Weak Acids

    Strong acids like hydrochloric acid (HCl) ionize completely in solution. When added to water, only H+ and Cl– are present, there is no HCl. The water’s pH does not affect solubility of a strong acid.

    But weak acids do not completely ionize. The water pH affects the degree of ionization and therefore solubility.

    Most herbicides are weak acids. A weak acid is one that does not dissociate completely in solution. A typical example of a weak acid functional group is carboxylic acid (-COOH). In solution, compounds with a carboxylic moiety exist in an equilibrium, with some as -COOH (containing the hydrogen, also called “protonated”) and others as -COO– and H+. In the dissociated form, the acid is more water soluble than in its protonated form due to the negative charge that makes it ionic.

    Weak acids have a dissociation constant known as the pKa. When the solution is at the molecule’s pKa, the acid is 50% dissociated. When the solution has a lower pH than the pKa, there is less dissociation and the protonated forms of the molecule dominate. That has two important implications for herbicides.

    • the molecule becomes less water-soluble at lower pH
    • the molecule has fewer opportunities to interact with positively charged items

     pH Dependent Solubility

    Water-solubility is a two-edged sword. On the one hand, having a highly water soluble product makes it easier to dissolve in water. This pays dividends when mixing a batch or cleaning a sprayer because a product formulated as a solution will easily go into a true solution and will stay mixed. Examples are glyphosate, glufosinate, and salts of 2,4-D, MCPA, and dicamba.

    On the other hand, most pesticides need to enter a plant to reach their site of action. And a plant cell, with its waxy cuticle and oily membranes, creates an effective barrier for water, and for water-loving molecules dissolved in it. As a result, a formulation that allows the water-soluble product to interact with an oily barrier is needed.

    The products that can do this are surfactants. Acting like detergents, surfactants have regions in their structure that are oil-loving (lipophilic) and other regions that are water-loving (hydrophilic). Surfactants can therefore bind to both oil and water and provide a bridge for water-soluble products across oily barriers.

    That’s also one of the reason that the most water-soluble products such as glyphosate and glufosinate contain a lot of surfactants in their formulation, reducing the concentration of active ingredient in the jug and possibly leading to foaming with agitation.

    Pesticides have a wide range of solubilities, and for some, water pH will play an important role. Below is a table of some water solubilities of selected herbicides.

             Solubility (ppm)
    Trade NameActive IngredientMode of Action GrouppH ~ 5pH ~ 7pH ~ 9
    Selectclethodim1535,45058,900
    Ally 2metsulfuron25502,800313,000
    Expresstribenuron2482,04018,300
    Pinnaclethifensulfuron22232,2408,830
    Everestflucarbazone244,00044,00044,000
    Simplicitypyroxsulam21632,00013,700
    Frontlineflorasulam20.1694
    Varrothiencarbazone2172436417
    Raptorimazamox2116,000 >626,000>628,000
    Pursuitimazethapyr22,570 12,8707,500
    2,4-D2,4-D salt429,93444,55843,134
    dicambadicamba salt4>250,000>250,000>250,000
    Roundupglyphosate9>500,000>500,000>500,000
    Libertyglufosinate10>500,000>500,000>500,000
    Heatsaflufenacil14302,100 >5000
    Distinctdiflufenzopyr19635,90010,550
    Infinitypyrasulfatole274,20069,10049,000

    Compare the solubility at pH 7 to that at pH 5. For most of these herbicides, water solubility is worse at lower pH. That is because they are more protonated and become more lipophilic.

    I’ve placed a lot of Group 2 products in this table because those products are most often implicated in tank cleanout issues. All Group 2 products in this table, with the exception of Everest (flucarbazone-sodium) have lower solubility at pH 5 than they do at pH 7. For some, like pyroxsulam and floarsulam, it’s a big change. Those products, when acifified, are prime candidates for poor mixability and poor cleanout.

    When it comes to dicamba, low pH has another side-effect. It makes the molecule more volatile, increasing danger to sensitive plants nearby. For that reason, acidification of dicamba in its Xtendimax and Engenia formulations is not permitted.

    Note that the Group 4 examples, 2,4-D salt and dicamba salt, as well as glyphosate and glufosinate, are highly water-soluble and pH has very little effect on that.

    Particularly for glyphosate, the claim that it becomes more oily at low pH and will therefore be taken up more easily, is not supported by these data. Considering that the most acidic pKa for glyphosate (it has four acidic groups) is 0.8, pH would need to be much lower for any noticeable impact on oilyness.

    Tank Mixability

    Given today’s environment of herbicide resistance, applications with multiple mode of action tank mixes are very common. Acidifying a spray mix to benefit one herbicide may create problems for its tank mix partners.

    If there is a concern that spray water is too alkaline, it is recommended that the pH of the finished spray mix be measured. Since many herbicides are weak acids, they will lower the pH of the mixture by themselves. For example, the addition of glyphosate to water with pH 7.5 will drop the pH to about 5 or so, depending on the water’s buffering capacity.

    As a result, glyphosate tank mix partners that are pH sensitive may suffer in the presence of glyphosate, and pH may actually need to be raised.

    pH Dependent Half-life

    Herbicides

    There are a lot of claims that pesticides break down rapidly in alkaline spray water. And yet, in my career working primarily with herbicides, I do not recall this ever being a problem in practice.

    Below is a table of herbicides for which I could find half-life information, with the help of this comprehensive list produced by Michigan State University.

    ProductActive ingredientHalf Life
    AtrazineatrazineMore stable at high pH
    BanveldicambaStable at pH 5 – 6
    BromoxynilbromoxynilpH 5 = 34 d; pH 9 = 1.7 d
    Fusiladefluazifop-p-butylpH 4.5 = 455 d; pH 9 = 17 d
    Libertyglufosinate-ammoniumStable over wide range of pH
    GramoxoneparaquatNot stable at pH above 7
    ReglonediquatpH 5 = 178 d; pH 7 = 158 d; pH 9 = 34 d
    MCPAMCPApH 9 = < 5 days
    PoastsethoxydimStable at pH 4.0 to 10
    PrincepsimazinepH 4.5 = 20 d; pH 5 = 96 d; pH 9 = 24 d
    ProwlpendimethalinStable over a wide range of pH values
    RoundupglyphosateStable over a wide range of pH values
    TreflantriflularinStable over a wide range of pH values
    2,4-D2,4-DStable at pH 4.5 to 7

    Note that all of the herbicides are relatively stable. Some are a bit less stable at high pH, but none of the listed herbicides is in danger of breaking down on the day it is being applied. Only one is actually unstable at high pH – paraquat, a herbicide no longer registered in Canada and resticted in many other countries. Those with short half-lives experience them at quite high pH which are rarely seen in practice.

    Insecticides

    Insecticides are a different story. Several are very sensitive to pH. This table is again adapted from a comprehensive list published by Michigan State University, here.

    Trade NameActive IngredientHalf-life
    AdmireImidaclopridGreater than 31 days at pH 5 – 9
    Agri-MekAvermectinStable at pH 5 – 9
    AmbushPermethrinStable at pH 6 – 8
    AssailacetamipridUnstable at pH below 4 and above 7
    AvauntindoxacarbStable for 3 days at pH 5 – 10
    Cygon/LagondimethoatepH 4 = 20 hrs; pH 6 = 12 hrs; pH 9 = 48 min
    CymbushcypermethrinpH 9 = 39 hours
    DiazinonphosphorothioatepH 5 = 2 wks; pH 7 = 10 wks; pH 8 = 3 wks; pH 9 = 29 days
    Dipel/Forayb. thuringiensisUnstable at pH above 8
    DyloxtrichlorfonpH 6 = 3.7 days; pH 7 = 6.5 hrs; pH 8 = 63 min
    Endosulfanendosulfan70% loss after 7 days at pH 7.3 – 8
    FuradancarbofuranpH 6 = 8 days; pH 9 = 78 hrs
    Guthionazinphos-methylpH 5 = 17 days; pH 7 = 10 days; pH 9 = 12 hrs
    KelthanedicofolpH 5 = 20 days; pH 7 = 5 days; pH 9 = 1hr
    LannatemethomylStable at pH below 7
    LorsbanchlorpyrifospH 5 = 63 days; pH 7 = 35 days; pH 8 = 1.5 days
    Malathiondimethyl dithiophosphatepH 6 = 8 days; pH 7 = 3 days; pH 8 = 19 hrs; pH 9 = 5 hrs
    Matadorlambda-cyhalothrinStable at pH 5 – 9
    Mavriktau-fluvalinatepH 6 = 30 days; pH 9 = 1 – 2 days
    MitacamitrazpH 5 = 35 hrs; pH 7 = 15 hrs; pH 9 = 1.5 hrs
    OmitepropargiteEffectiveness reduced at pH above 7
    OrtheneacephatepH 5 = 55 days; pH 7 = 17 days; pH 9 = 3 days
    PouncepermethrinpH 5.7 to 7.7 is optimal
    PyramitepyridabenStable at pH 4 – 9
    Sevin XLRcarbarylpH 6 = 100 days; pH 7 = 24 days; pH 8 = 2.5 days; pH 9 = 1 day  
    SpinTorspinosadStable at pH 5 – 7; pH 9 = 200 days
    Thiodanendosulfan70% loss after 7 days at pH 7.3 to 8
    ZolonephosaloneStable at pH 5 – 7; pH 9 = 9 days

    Among insecticides, dimethoate, amitraz, and malathion stand out as breaking down rapidly in alkaline water. For these products in particular, it may be important to acifify the spray mix if there is any delay in spraying.

    Recommendations

    I’ve never been a fan of messing with solution pH unless recommended on the product label. Even when there is evidence that lower pH improves efficacy, consider the impact on tank mix partners.

    We’ve seen improvements in solubility and tank cleranout of Group 2 products with raised pH, and ammonia is the most cost-effective way to achieve that. But again, following label recommendations is strongly recommended. The consequences of changes in pH, particularly acifification, can be very detrimental. To be safe, consider doing a jar test before committing to a whole tank to a pH adjustment.

  • How to Interpret a Water Quality Test Result

    How to Interpret a Water Quality Test Result

    It’s common advice: Test your water before using it as a spray carrier. You dutifully sample the well or dugout and await lab results. And what comes back is a whole lot of numbers. How to make sense of it all?

    Three examples of water test results conducted by labs in Canada

    All three of these tests report a large number of properties and identify specific minerals and other solutes. Which ones are important in spraying? Here is the order in which I look at the numbers.

    Conductivity: This property is usually expressed as micro Siemens per cm (µS/cm) and simply identifies how many ionic solutes are in a sample (watch for alternate units such as mS/cm and convert if necessary). It doesn’t differentiate between any minerals or other molecules, and therefore has limited information. But it does tell us if there is a large or small issue with water quality. If conductivity is below 500 µS/cm, the water is probably good for spraying. If the value is around 1000 to 2000, further investigation is necessary. Some water samples return conductivity of more than 10,000 µS/cm, and it’s important to identify which salts are causing that problem.

    Note that Total Dissolved Solids (TDS) are often listed, and these are related to conductivity. A common way to get TDS is to multiply conductivity by 0.65. The conversion factor depends on which salts are dissolved but the bottom line is that TDS and conductivity are closely related.

    Bicarbonate: Bicarbonates are HCO3 and their concentration is measured in milligrams per Litre (mg/L), which is the same as parts per million (ppm). Bicarbonates can antagonize Group 1 modes of action and the common threshold is 500 ppm. Research at NDSU has shown that Urea -Ammonium-Nitrate (UAN or 28-0-0 liquid fertilizer) can reduce bicarbonate antagonism in some Group 1 herbicides.

    Bicarbonates are negatively charged and are associated with a positive ion, often the hard water cations sodium (Na), calcium (Ca) or magnesium (Mg). As such, waters that are high in bicarbonates are often also hard.

    Total Hardness (calculated): This is one of the important parameters. Hardness antagonizes most weak acid herbicides, most importantly glyphosate and g;ufosinate, and also ties up surfactants and emulsifiers which can result in problems with mixing and compatibility. Hardness is caused by metal cations, in order of strength these are iron (Fe++), magnesium (Mg++), calcium (Ca++), sodium (Na+), and potassium (K+). Of these, Mg and Ca are typically most abundant, although some water is high in Na.

    The Total Hardness (ppm) reported in water tests is done by taking the most common two cations, calcium and magnesium, and using this formula: 2.497*Ca + 4.118*Mg. Note that some tests report hardness in Grains per Gallon, in this case, multiply grains by 17.1 to get ppm.

    While this calculation usually gives an accurate prediction of hardness, you may need to have a look at iron and sodium as well. Iron is less common, but some well waters are high in sodium or potassium. These minerals are not captured in the Total Hardness measurement. A water test low in Total Hardness may still be high in sodium, these are typically the samples with high conductivity.

    The threshold for Total Hardness depends on the herbicide, its rate, and the water volume. The most common quoted values are 350 ppm for the lower rates of glyphosate (1/2 L/acre equivalent), and 700 ppm for the higher rates. Lower water volumes increase the concentration of herbicide, and reduce the impact of water hardness or bicabonates.

    pH: This parameter is a bit over-rated because it is later affected by the herbicide and adjuvant dissolved in it. There is usually no concern with pH between 6 and 8, and water is rarely outside this range. It is best not to change the pH of water unless it is required on the label for mixing, because some products require low, and others require high pH for optimum solubility. Compatibility is an ever greater concern as our tank mix complexity increases.

    Water Conditioners

    The most common water conditioner is ammonium sulphate [AMS, (NH4)2 SO4]. In its pure form (21-0-0-24), a concentration of 1% to 2% w/v (8 to 17 lbs AMS/100 US gallons of spray water) solves most hard water and bicarbonate issues. Be cautious of using too much AMS (>3%), when added at high concentrations to some herbicides it can burn crops.

    Research has shown that AMS works in two ways: The sulphate ion binds with hard water cations, forming an insoluble precipitate that prevents the antagonistic cations from binding to, and inhibiting, the herbicide. The ammonium ion has been shown to improve cellular uptake by weak ion herbicides.

    Some product labels call for UAN as an adjuvant. UAN contributes ammonium, but not sulphate ions. As a result, while it may improve herbicide performance, it does not remove antagonizing cations from the mixture.

    Acids have been used to combat hard water. Most common herbicides are weak acids, and the acid constituent, usually a carboxilic acid, has a unique pKa. The pKa is the pH at which half the molecules are protonated (contain a hydrogen atom, resulting in an uncharged acid constituent) and the other half are not protonated (negatively charged). If the spray mixture has a pH below the pKa, the weak acid herbicides become protonated. This means the herbicide becomes less water-soluble, but also that it has less chance of interacting with a hard water cation. Acids that work in this way are less effective at ameliorating the effect of hard water than AMS.

    A small group of acids that includes citric acid and sufphuric acid can sequester or bind with hard water cations. But they do not contribute the ammonium ion that assists in weak acid herbicide uptake.

    If your water is questionable for spraying, there are four common choices:

    • Select a different well or dugout
    • If the problem is barbonates or hardness, treat water with a conditioner such as Ammonium Sulphate (AMS), available in pure form as 21-0-0-24. Some acids (citric, sulfuric) can form conjugate bases with hard water cations, removing them from solution. But the associated significant lowering of pH should be treated with an abundance of caution as it may affect solubility of some pesticides.
    • Reduce water volumes or increase herbicide rates.
    • Use a municipal treated water source or invest in a reverse-osmosis (RO) system. RO is neither cheap nor fast and requires additional investment in storage, and a way to deal with solute-enriched waste water. But it may be the best option for some.

    An Ammonium Sulphate calculator, originally developed by Winfield United using data from NDSU, can be downloaded here:

    AMS-Calculator-Sprayers101-1Download

    An excellent resource for adjuvant and water quality topics is this addendum in the North Dakota State University Guide to Weed Control.

    Using good quality water lowers the likelihood of problems with mixing and overall performance and that pays significant dividends later.