Category: Spray Basics

  • Remove and scrub your filters – Even when you use Dawn

    Remove and scrub your filters – Even when you use Dawn

    This article was co-developed by Mike Cowbrough, OMAFRA Weed Management Specialist in Field Crops

    Why scrub filters?

    Why do we ask you to manually scrub residue from sprayer filters and housings before changing chemistries? Here are three reasons why rinsing in-place may not be good enough:

    • There is potential for biologically-active levels of residue to persist in filters, even after a triple rinse, that could harm the next crop sprayed.
    • Persistent residues could cause physical antagonism with the chemistry you use next. This can cost time and/or efficacy should it plug filters and nozzles or reduce spray uniformity.
    • Persistent residues could cause chemical antagonism with the chemistry you use next – even several batches later. This could harm crops when the residue carried over from a much earlier application suddenly becomes soluble again thanks to detergents or pH adjusters in subsequent tank mixes.

    An experiment

    To some, the previous statements may seem excessive. Many sprayer operators claim that scrubbing filters is time consuming, or that they’ve never had a problem before, or that the tiny amount of residue they see in the filters after rinsing couldn’t possibly cause damage. We decided to test the efficacy of rinsing filters without removing them.

    We constructed a table-top system that could circulate chemistry through a 50 mesh filter. Think of it as a scaled-down sprayer that returns solution to the tank rather than spray it out. It replicates what the line filters on a larger sprayer might experience during a typical spray day.

    Table-top system to circulate spray mix at 1 gallon per minute through a 50 mesh filter.

    The method

    The tank (i.e. the bucket) would be filled with a tank mix and circulated through the filter to replicate a spray day. The contaminated filter could then be sampled to establish a baseline, and then alternately contaminated and rinsed in place to compare how much residue remained. Specifically, we would drop the filter housing and scrub all surfaces in 500 ml of water to collect any and all residue.

    Each sample collected would be poured through a filter for a visual check of residue. A small volume would be reserved to be sprayed on soybean and white bean seedlings as a bio assay of activity.

    The process

    We used Sencor (metribuzin) mixed at a rate that represented the low end of the label: 250 grams of product per acre at 5 gallons per acre. Not knowing what to expect, we circulated the solution through the filter for 20 minutes pumped at a rate of 1 gallon per minute and peeked into the tank.

    After 20 minutes of circulation, Sencor began to foam.

    Seeing that we were creating foam, we decided to add defoamer. Then we peeked into the filter housing to see what had accumulated so far.

    Very little residue was found on the filter or in the housing after 20 minutes of circulation.

    Finding very little in the way of residue, we chose to let the system circulate for an hour. We felt this would represent a single real-world tank’s worth of product. Since we’d added defoamer, we decided it was safe to leave the lab and let the system circulate…

    Foam overs: No fun in the field and no fun in the lab.

    Despite having added defoamer, we had a mess to clean up. When we opened the bucket we noted all the product clinging to the lid (see below). We collected some of this scum to replicate what might be clinging to parts of the spray tank that are not adequately covered by rinse-down nozzles. We then dropped the filter into 500 ml of water and scrubbed the housing and filter to collect any and all residue.

    Collecting residue from the bucket lid to replicate what might remain in a tank that is not sufficiently rinsed.

    We then added additional defoamer and checked in regularly as we circulated the mixture for several hours to replicate a full day of spraying. This time when we checked to see how much residue we had collected, found a surprising amount.

    Residue following several hours of circulation, prior to triple rinsing with water.

    We replaced the filter and performed a triple rinse with water before dropping the filter to collect our residue sample. As shown below, the triple rinse cleared much of the residue, but trace amounts were still visible.

    Residue following several hours of circulation and a triple rinse with water.

    Dawn Detergent and the 5 Second Squeeze

    We refilled the tank with Sencor and defoamer and circulated it for several hours to once again contaminate the filter. This time, however, we added detergent to the second rinse. We did this in response to claims that Dawn dish detergent removed residues from dry products such as Atrazine without having to drop the filters.

    A former agrichemical rep explained that the practice likely originated in Western Canada some years ago when several growers suddenly experienced physical incompatibilities with a particular batch of dry product. It was suspected that the problem was due to abnormally cold temperatures during mixing, but the result was that many were left with solids in the tanks that could not be flushed.

    Ionic surfactants are found in “cheap and nasty” shampoos, dish detergents and car care products. They can be tough on the skin, but they are of higher surfactantcy than NIS. And so, agrichemical reps bought pallets of Dawn dish detergent (Branded “Fairy” in the UK) from big box stores and found it broke the solids down sufficiently to flush the tanks. From there, it is likely growers started adding it during the rinse to facilitate cleanout. But, is the “Five second squeeze” a myth or does it work?

    Results

    Adding Dawn detergent to the second rinse reduced visible residue in the filter housing and on the plastic sides of pop bottles that stored the rinsate.

    We saw a visible reduction in the filmy residue left behind by Sencor in the filter housing and on the walls of the pop bottles used to store the rinsate. It was easy to see why the 5 second squeeze appeared to improve matters… but was there enough residue to still there to cause trouble?

    Rinsate filtered through red cloth for a visual check of residue.

    We poured the rinsate from each sample through red cloth. There was little or no visible evidence of Sencor in the sample taken from the lid of the filter following an hour of spraying (left), or our baseline sample of a filter contaminated after an hour of circulation with no rinse (second from left). There was a great deal in the sample from the filter following “a day’s spraying” and a triple rinse (second from right), and less in the triple rinse containing detergent (right). These last two conditions are compared below.

    Following several hours of spraying, residue following a triple rinse with water (left) and a triple rinse with detergent in the second rinse (right).

    A volume of the rinsate from each sample was reserved for bio assay on soybean seedlings. The filter in the spray booth was cleaned thoroughly between conditions.

    The following images show that even when there was little or no visible residue, there was still sufficient activity remaining to injure, or in the case of the triple rinse with water, kill soybean seedlings.

    Summary

    Bear in mind that this is a single experiment with a single chemistry, but it does support the following observations:

    • Always rinse the sprayer as soon as possible and pay attention to dead-end plumbing and filters. Diligence is a function of knowing what was sprayed last, what is coming next, and the sensitivity of the crops being sprayed.
    • Cleaners do not decontaminate – they loosen residues to make rinsing more effective. In our experiment, Dawn detergent appeared to reduce residue and that will keep you spraying plug-free for longer. But, the bioassay showed sufficient activity remained to cause carry-over damage.
    • A triple rinse with water may be insufficient to remove residue from filters. Even if the residue left behind does not cause damage in the next crop sprayed, it can persist and has the potential to react antagonistically with subsequent sprays.

    Bonus: Pro Tips

    Not long after publishing this article, we were contacted by a grower who had difficulties with clay-based products plugging up his filters. It took a carry-over incident to convince him he needed to address the problem, so he installed $20 ball valves at the bottom of the filter housings. This isn’t as good as dropping and scrubbing filters, but opening and closing the valve under pressure during rinsing blew the filters clear of visible residue. Others have noted similar modifications on the pump of their tender truck to clear the filter of algae.

    Other options include a hydraulic-style ball valve (stronger than plastic). Or, install a gator lock cam after the valve and insert a plug so if it’s accidentally opened it won’t dump the tank. Just keep a hose in the toolbox and insert it when you need to flush. Finally, one grower added a Thompson strainer to the sprayer and removed the screens from the Banjo Y’s. He ran a 1″ hose from the Thompson to a valve by the work station and cracks it open as part of every rinse.

    A cheap and effective solution for clearing filters of residue. Not as good as dropping and scrubbing, but a great compromise.
    Ball valves tend to protrude below the sprayer, so they may catch high corn. Be careful.
  • Airblast Agitation and Solubags

    Airblast Agitation and Solubags

    Agricultural products are formulated to be as emulsifiable as possible, but many do not mix well in water. They contain elements that do not dissolve (e.g. wettable powders), or they may be petroleum distillates (e.g. emulsifiable concentrates). Other products are heavier than water and form precipitates (e.g. fertilizers and powdered metals like copper). Consequently, good agitation is very important.

    Effective agitation requires water to “sweep” the bottom of the tank so that any precipitated material is picked up and re-mixed. Turbulence is often not enough. If there is too little agitation, the pesticide will be applied unevenly and not always at the required rate. If there is too much agitation, the pesticide may foam (which can be controlled using anti-foamers) or cause an invert emulsion (a gel). There are two types of airblast sprayer agitation: Mechanical and Hydraulic (learn about pros and cons here).

    Mechanical Agitation

    Mechanical Agitation is produced by paddles that are attached to a shaft mounted near the bottom of the spray tank. While effective, this system cannot always sweep the very bottom of the tank, so there is always some material that precipitates out of reach. Are your nozzles and screens plugging frequently, and is there “sludge” left at the bottom of the tank after spraying? You may have an agitation issue.

    Note the two paddles set at 90° to one another on the mechanical agitation shaft in this very cool “cutaway” Turbomist sprayer.
    Note the two paddles set at 90° to one another on the mechanical agitation shaft in this very cool “cutaway” Turbomist sprayer.

    Hydraulic Agitation

    Hydraulic Agitation is accomplished by returning a portion of the pump output to the tank. Cylindrical and oval tanks are the ideal configuration for the sparging (i.e. rinsing) type of hydraulic return agitation system. This system consists of a tube located longitudinally along the wall of the tank, with volume booster nozzles aimed at the centreline so they sweep across the bottom. Volume booster nozzles take a small amount of water pumped into their venturi chamber and create a vacuum that draws three to four times that volume from the surrounding water and expels it out the end.

    For hydraulic agitation to the effective, the agitator nozzle(s) should be fed by a dedicated line from the pressure side of the pump (not the pressure regulator). They should have a valve to throttle the flow or completely shut it off to prevent foaming.

    A mixing nozzle in the basket of a Hol sprayer.
    A mixing nozzle in the basket of a Hol sprayer.
    With enough pump capacity, a hydraulic return in the tank basket is a great way to agitate as you mix. A return in an old FMC.
    With enough pump capacity, a hydraulic return in the tank basket is a great way to agitate as you mix. A return in an older FMC.

    Adding Water Soluble Pouches

    Adding pesticide to the sprayer may not always be straight-forward. Many airblast operators, for example, place dissolvable pouches in the basket so they can be broken up by the hydraulic return, or the fill water. But fill water often splatters out of the basket, and the bags can burst open, releasing product into the air. This creates unnecessary contamination and both inhalation and dermal exposure concerns.

    Photo credit: Mario Lanthier.
    Photo credit: Mario Lanthier.

    Some elect to temporarily remove the basket and add the pouches to a half-full tank with the agitator on. However, the pump can suck in the partially dissolved bag which then coats the intake screen. This is exacerbated when the fill water is cold. I know of one operator that had to rebuild the pump because the Viton seals burned out. This operator now adds pouches to the basket while standing upwind and away from potential splatter. Or, they mix a pre-slurry.

    Mixing a pre-slurry requires the operator cut the bag into a five or 10 gallon bucket filled with water and to incorporate using a paint mixer. However, mixing a pre-slurry increases the chances of dermal exposure, inhalation and point-source contamination. Dissolvable bags were intended as a form of closed transfer, which is a good idea. Mixing a pre-slurry defeats that intent.

    And so, for all these reason, I don’t feel dissolvable pouches are a good formulation choice. If possible, select product formulations that do not cause possible filling issues and better match the capabilities of your agitation system. Always choose the safest and most effective filling method for your sprayer design.

  • Exploding Sprayer Myths (ep.12): The Buffer Zone

    Exploding Sprayer Myths (ep.12): The Buffer Zone

    In this episode of Exploding Sprayer Myths we reduce a complicated best practice to black and white… literally. Watch as Jason and Tom get a creepy lesson in the do’s and do not’s of no-spray areas. Under the watchful eye of Dr. Jim Todd (OMAFRA Industrial Crops Specialist and Rod Serling cos-player), brace yourself as you enter The Buffer Zone.

    Learn more about how vegetative filter strips mitigate runoff on this Health Canada webpage.

    Thanks to the staff at the Simcoe Resource Station and to RealAgriculture for making this video possible.

    And if you’re curious about the kitchen-appliance cameo, you’ll have refer back to earlier episodes.

  • Exploding Sprayer Myths (ep.11): Drift

    Exploding Sprayer Myths (ep.11): Drift

    This video won the Gold 2019 Canadian Farm Writers Federation’s Jack McPherson Award for Electronic Media. This award is for the best video, news story or feature broadcast by a Canadian medium less than 15 minutes in length on an agricultural topic. We’d like to thank Jason Strove, Bern Tobin and the whole team at RealAgriculture for helping to bring Exploding Sprayer Myths to life.

    Welcome to season four of Exploding Sprayer Myths, featuring a new opening sequence and a special guest star. Have fun accidentally learning about reducing pesticide drift as we poke fun at Canadian and Australian stereotypes. If you’re unfamiliar with the McKenzie Brothers and the Great-White North, then be sure to educate yourself here before you take off, eh?

    Beauty.

    Thanks to Mary O’Brien (@SprayDriftGirl) and the Simcoe Research Station.

  • Rainfastness of Insecticides and Fungicides on Fruit

    Rainfastness of Insecticides and Fungicides on Fruit

    This article was co-authored by Kristy Grigg-McGuffin, OMAFA Horticulture IPM Specialist

    In view of the frequent heavy rains in many regions this season, understanding rainfastness, or the ability of a pesticide to withstand rainfall, is important to ensure proper efficacy. All pesticides require a certain amount of drying time between application and a rain event. Typically, residue loss by wash-off is greatest when rain occurs within 24 hours of spraying. After this point, the rainfastness of a product will depend on formulation, adjuvants and length of time since application.

    Rainfastness of Insecticides

    John Wise, Michigan State University has studied rainfastness of common tree fruit insecticide groups and his findings are summarized below. For the complete article, refer here. Note that some products listed in this article may not be registered for use in Canada. Check with your local supplier or in Ontario, refer to OMAFA Publication 360 for a complete list of registered products.

    According to Wise, the impact of rain on an insecticide’s performance can be influenced by the following:

    1- Penetration

    Penetration into plant tissue is generally expected to enhance rainfastness.

    • Organophosphates have limited penetrative
      potential, and thus considered primarily surface materials.
    • Carbamates and pyrethroids penetrate the cuticle,
      providing some resistance to wash-off.
    • Spinosyns, diamides, avermectins and some insect
      growth regulators (IGR) readily penetrate the cuticle and move translaminar (top
      to bottom) in the leaf tissue.
    • Neonicotinoids are considered systemic or
      locally systemic, moving translaminar as
      well as through the vascular system to the growing tips of leaves (acropetal
      movement).
    • For products that are systemic or translaminar,
      portions of the active ingredient move into and within the plant tissue, but
      there is always a portion remaining on the surface or bound to the waxy cuticle
      that is susceptible to wash-off.

    2- Environmental persistence and inherent toxicity

    Environmental persistence and inherent toxicity to the target pest can compensate for wash-off and delay the need for immediate re-application.

    • Organophosphates are highly susceptible to
      wash-off, but are highly toxic to most target pests, which means re-application
      can be delayed.
    • Carbamates and IGRs are moderately susceptible
      to wash-off, and vary widely in toxicity to target pests.
    • Neonicotinoids are moderately susceptible to
      wash-off, with residues that have moved systemically into tissue being highly
      rainfast, and surface residues less so.
    • Spinosyns, diamides, avermectins and pyrethroids
      are moderate to highly rainfast.

    3- Drying time

    Drying time can significantly influence rainfastness, especially when plant penetration is important. For instance, while 2 to 6 hours is sufficient drying time for many insecticides, neonicotinoids require up to 24 hours for optimal penetration prior to a rain event.

    4- Adjuvants

    Spray adjuvants that aid in the retention, penetration or spread will enhance the performance of an insecticide.

    The following tables can serve as a guide for general rainfastness to compliment a comprehensive pest management decision-making process. They are adapted from “Rainfast characteristics of insecticides on fruit” by John Wise, Michigan State University Extension.

    Based on simulated rainfall studies to combine rainfastness with residual performance after field-aging of various insecticides, including carbamates (Lannate), organophosphates (Imidan, Malathion), pyrethroids (Capture), neonicotinoids (Assail, Actara, Admire), IGRs (Rimon, Intrepid), spinosyns (Delegate) and diamides (Altacor), Wise recommends the following re-application decisions for apples. Additional work was done on grapes and blueberries; see Wise’s article for this information. Among the crops, variation in rainfastness of a specific insecticide occurs since the fruit and leaves of each crop have unique attributes that influence the binding affinity and penetrative potential.

    • ½ inch (1.25
      cm) rainfall:       All products with 1-day old residues could withstand ½ inch
      of rain. However, if the residues have aged 7 days, immediate re-application
      would be needed for all products but Assail, Rimon, Delegate or Altacor on
      apples.
    • 1-inch (2.5
      cm) rainfall:       In general, most products would need re-application following
      a 1-inch rainfall with 7-day old residues, whereas Delegate and Altacor could
      withstand this amount of rain on apples and would not need to be immediately
      re-applied. Some products such as Imidan on apples could withstand 1 inch of
      rain with 1-day old residues.
    • 2-inch (5
      cm) rainfall      : For all products, 2 inches of rain will remove enough
      insecticide to make immediate re-application necessary.

    It is important to note, not all products registered for the selected pests were included in this study. Refer to Publication 360 for a complete list of management options.

    Rainfastness of Fungicides

    There is no comparable research on rainfastness of fungicides and few labels provide this kind of information. A general rule of thumb often used is that 1 inch (2.5 cm) of rain removes approximately 50% of protectant fungicide residue and over 2 inches (5 cm) of rain will remove most of the residue. However, many newer formulations or with the addition of spreader-stickers, some products may be more resistant to wash-off. Avoid putting on fungicides within several hours before a rainstorm as much can be lost to wash-off regardless of formulation. As well, there are exceptions to the general rule in regard to truly systemic fungicides such as Aliette and Phostrol.

    The effectiveness of sticker-spreaders with fungicides is variable and product/crop specific. Penetrating agents don’t help strobilurins; in fact, some fungicide/crop combinations have been associated with minor phytotoxicity due to excessive uptake. Captan, which is intended to stay on the surface, is notorious for causing injury when mixed with oils or some penetrating surfactants that cause them to penetrate the waxy cuticle.  Consult labels for minimum drying times for individual products and recommendations for using surfactants. 

    Annemiek Schilder, Michigan State University suggests the following to improve fungicide efficacy during wet weather:

    • During rainy periods, systemic fungicides tend
      to perform better than protectant (or contact) fungicides since they are less prone
      to wash-off.
    • Applying a higher labelled rate can extend the
      residual period.
    • Apply protectant fungicides such as captan
      (Supra Captan, Maestro), mancozeb (Manzate, Dithane, Penncozeb) and metiram
      (Polyram) during sunny, dry conditions to allow for quick drying on the leaves.
      These types of fungicides are better absorbed and become rainfast over several
      days after application.
    • Apply systemic fungicides such as sterol
      inhibitors (Nova, Fullback, Inspire Super), SDHI (Fontelis, Sercadis, Kenja, Aprovia
      Top, Luna Tranquility) and strobilurins (Flint, Sovran, Pristine) under humid,
      cloudy conditions. The leaf cuticle will be swollen, allowing quicker
      absorption. In dry, hot conditions, the cuticle can become flattened and less
      permeable, so product can breakdown in sunlight, heat or microbial activity or
      be washed off by rain.

    Click here to refer to the complete article.