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.
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.
When it comes to information about mitigating pesticide drift, it’s plentiful and easily accessed. I have an archive of >30 articles written by Ontario Ministry of Agriculture staff spanning 1999 to present day. Many are on this website. In fact, there’s so much good information out there (see BeDriftAware) it feels like there’s nothing left to say. As a connoisseur (and author) of such materials, I’ve noticed they can be grouped into four common themes – see if you recognize any:
The Carrot: These articles describe the benefits of reduced drift, like solid neighbourly relations, reduced environmental impact, saving money in wasted pesticide and improved spray coverage.
The Stick: These articles feature insurance adjusters or regulators providing statistics from case studies on the financial, legal, and insurance impacts of drift. Not to mention the time it takes to deal with these issues.
The Heart: Many articles describe the frustration and emotional impact from the driftee’s perspective. Others chronicle the conflict, irritation and personal insult that come from being accused of drifting.
The Facts: Here we have technical specialists laying out math, such as weather models describing spray behaviour, buffer zones and drift reduction technologies like nozzles, shrouds and sprayer calibration.
Beyond the written word there are also videos, PowerPoint presentations, workshops or demonstrations, government fact sheets, marketing brochures, social media content and smartphone apps. And yet, every May-July, the drift complaints seem to roll in regardless. For those that ask “why?” here are a few possible reasons:
Why drift happens
Maybe the sprayer operator is pressed for time and chooses to ignore best practices in an effort to catch up. Haste can lead to mistakes.
Perhaps the sprayer operator is new and inexperienced, or falls into that small demographic without ready access to educational resources like ag meetings or the internet.
Maybe the operator is a veteran lulled into false security having successfully sprayed so many acres, for so many hours, for so many years. Why be so diligent when nothing bad ever seems to happen? Bad logic, but not uncommon.
Maybe the problem stemmed from poor communication. Perhaps the land is rented by one person, to a farmer that isn’t there, who has their fields sprayed by custom applicators, who don’t know what’s around the field.
Or, perhaps, even the best-intentioned sprayer operator can have bad luck.
Where can drift take place?
Agricultural spray (i.e. field crop or horticulture) has the potential to move between operations, or onto residential areas, or sensitive environmental areas. A single operation can even drift an incompatible chemistry onto itself. There are also residential applications (e.g. lawn care) that can negatively affect neighbours. Industrial applications such as roadside sprays can drift to agricultural or residential. Even organic operations spray products that can move outside the treatment area if conditions allow.
It is important to recognize that every single spray application has the potential for off-target movement. That’s why it’s so important to know what and who is around the treated area.
Communication helps
Communication between neighbours can make a big difference, both in preventing drift damage and resolving matters should an incident occur. Here are two perspectives on the same chemical trespass incident. In the first, the parties do not know, and do not care to know, one another. In the second, the parties have communicated previously. Which scenario will be easier to resolve?
A “field cropper that drives 20 miles per hour in high winds” is contacted by a MECP officer on behalf of a “vegetable grower that’s always complaining about spraying”. Accusations and defensiveness between the two parties escalate until they prevent them from speaking directly. Specialists, adjusters, and the officer find themselves acting as mediators. The process is slow and likely headed for court.
Sarah knocks on Kevin’s door and says there might be something wrong with her crop – can he come have a look? She has (rightfully) contacted the MECP to collect samples just in case, and Kevin has all his spray records so they can figure it out. They call in a crop consultant and she contacts a university specialist to solve the problem and prevent it happening again. They follow the crop to yield to determine the impact and agree on a settlement between them.
Regarding Scenario 1, it’s not my intention to slander field croppers or horticulturalists; I have actually heard parties involved in highly emotional drift disputes describe one another this way. My intent is to point out that you cannot label an entire industry based on the actions of an individual. When parties see each other in this fashion they are unlikely to work together to resolve the problem. No one will be satisfied with the outcome.
Regarding Scenario 2, I have observed that once each party has a face and a name, it’s so much easier to find solutions. It doesn’t mean someone wasn’t at fault or that compensation isn’t required, but the dialogue facilitates a faster, easier and less emotional outcome. Obviously, in the case of repeated or large-scale incidents, communication may not yield satisfactory results. I’m hopeful, but not naive.
Opening a dialogue
Communication can be initiated from either direction: An applicator can inform a residential neighbour or fellow farmer with sensitive crops when and what they intend to spray. Likewise, the neighbour or sensitive crop grower can reach out to the applicator to let them know they are there and that they are concerned.
There’s no need to wait until there’s a problem. Both parties benefit from keeping one another informed about when sprays go on and the state of any sensitive crops. And, if there is an issue, both parties should begin documenting conditions and suspected damage as soon as possible and over time during the resolution.
So, the core of this article isn’t how to prevent drift, or what to do if you suspect it. That’s all been said and I’ve listed a few resources for reference at the end. This article is about being aware of drift potential and about opening lines of communication between those that share borders.
So follow the links below to learn more about what you can do to mitigate drift. Then, go introduce yourself to your neighbours. Bring a pie. Everyone loves pie.
Resources
Article – This link includes four videos and a factsheet about what drift is, how to prevent it and what to do if you suspect it.
Article – This link includes a video and a factsheet about surface inversions and drift.
Website – This is a link to BeDriftAware, a collection of resources and tools to encourage the use of best application practices by farmers and sprayer operators to reduce the possibility of spray drift.
When warm air is cooled, it loses some of its moisture-holding capabilities. This change often occurs at night, when plants (and other objects) cool. Once the temperature of the surface of the leaves, for example, drops below the dewpoint, it causes water to condense, forming the shiny dew that causes so many to question early morning spray applications.
The question is often: will the spray run off the plant or will it get so diluted that it doesn’t work anymore?
In a dew chamber, work has shown that large spray droplets are more likely to run off a plant saturated with dew than their smaller counterparts. However, similar work showed that spray efficacy was not altered by droplet size.
Wolf discusses this work and the potential answer to the seemingly conflicting findings. Wolf also explains how grassy weeds compare to broadleaves, the role of surfactants, and what to consider when making the decision to spray through dew or not.
One of the pleasures of working in agricultural extension is when you’re able to help a grower solve a problem. This was one of those happy occasions. An orchardist purchased a Lipco multi-row recycling sprayer and wanted help evaluating their spray coverage.
We worked in 3.7 m (12 foot), mature, high-density Royal Gala trees. The sprayer was driving at 5.0 km/h (3.1 mph), operating at 11 bar (160 psi) using orange Albuz 80 degree air-induction flat fans. This resulted in about 350 L/ha (~37 gpa).
This grower wisely invested in the air-assist option, which produces a vertical plane of somewhat laminar air to entrain the spray and carry it into the centre of the target canopy. Whatever spray blows through the tree should impact the opposing shroud and get recycled back to the tank. All in all, how could you miss?
…we managed to.
Water sensitive papers were placed back-to-back facing each alley (in other words, facing the spray booms). Despite our best efforts, each pass resulted in inconsistent coverage. Papers were replaced in the same location and orientation for each pass and no settings were changed. Nevertheless, sometimes a paper got spray and sometimes it didn’t. What was going on? It was as if the two air streams were interfering with one another – almost cancelling each other out.
Air from tangential (cross-flow) fans oriented perpendicular to the canopy in direct opposition will cancel out. This reduces canopy penetration.
Where possible, do not position laminar air outlets in direct opposition. The convergence creates a high-pressure zone that reduces spray penetration. Some sprayers are designed to avoid this by staggering air outlets one ahead of the other. Laminar flows will deflect unpredictably around this pressurized area and carry droplets back out of the canopy. Unless the canopy is particularly narrow and sparse, turbulent air handling systems do not typically create this problem. In both cases, canopy penetration is improved when fans are staggered and/or are angled slightly forward or backward.
Grey arrows indicate direction of travel. The air outlets of wrap-around sprayers should be symmetrical when viewed from behind. A. Tangential fans in direct opposition: Poor coverage. B. Tangential fans angled forward/backward: Possible vortices and good coverage. C. Tangential fans angled backward: Good coverage, but if the angle is too steep, air will not penetrate the canopy. D. Straight-through axial fans in direct opposition: Good coverage in denser canopies. E. Straight-through axial fans angled slightly backward: Good coverage but limit the angle to prevent the trailing edge of the air wash from missing the canopy entirely. F. Straight-through axial fans angled forward: Slight angles are acceptable, but too much in this image. Wind created by travel speed subtracts from air energy. This creates a risk of reduced coverage and increased operator exposure.
We decided to turn the outer boom/shroud/fan assemblies 10˚ backward by loosening the four bolts at the top of the gantry (see below). This minor change in configuration improved spray coverage significantly. Increasing the angle beyond 10° might have caused the air wash to trail along the canopy face and would have made sprayer turns difficult at the row ends.
We loosened the four clamping screws to adjust the fan angle on the outer boom of this Lipco Recycling Tunnel sprayer.
We replaced the water sensitive papers and ran another pass. The operator later told me he could see the leaves and branches rustling in the row where we made the adjustment, but not in the unadjusted row. The result on water-sensitive paper was dramatic.
Since experiencing this in 2013, I have been told that the Lipco instruction manual advises against air in direct opposition. It was a poorly translated and somewhat obscure sentence buried in the manual, but I concede that it was there. Determine whether your sprayer produces more laminar or more turbulent air, and explore how their relative orientation impacts canopy penetration.
