Tag: pesticide

Thermal Inversions for Sprayer Operators
In April 2014, NDSU extension published an excellent factsheet explaining what thermal inversions are, how to detect them and how they affect pesticide spray drift. That factsheet inspired this article.
The Atmosphere
The Earth is surrounded by a layer of air called the atmosphere. Think of it as a sheet of liquid percolating and flowing over the Earth’s surface. Seems a bit precarious, doesn’t it?
We define “layers” of atmosphere based on their distance from the Earth’s surface (see image below). We’ll focus on the lowest part of the Earth’s atmosphere: the Surface Boundary Layer. As it drags along the Earth’s surface it experiences rapid changes in wind speed, temperature and humidity (on a time scale of an hour or less).
The Earth’s Atmosphere. The illustration of the Earth is to scale, but obviously the landscape is not. Our focus in on the Surface Boundary Layer.
Atmospheric temperature
In relatively calm, clear and dry conditions (e.g. a nice afternoon), air cools with elevation at a rate of about 1°C per 100m. This change is called the Adiabatic Lapse Rate and it’s caused by pressure changing with elevation. If your ears have popped when driving down a steep hill, you’ve experienced pressure change with elevation; there is more atmosphere overhead and the weight pushes down.
With higher elevation, there is less atmosphere overhead. Less weight means less pressure and this gives air room to expand. Expansion takes work and work costs energy, which creates a cooling effect. See how simple thermodynamics are?
In the graph below, the red line shows the Adiabatic Lapse Rate of air cooling with elevation. The blue line indicates wind stirring and homogenizing the atmosphere, reducing the degree of temperature change with elevation (more on that later).
Day and night
When we add the effect of daytime solar heating and nighttime cooling, the rate of temperature change is affected. Let’s consider how this works on a clear, relatively calm day:
Early morning
The morning sun emits short wave radiation, which is absorbed by the Earth’s surface. The surface conducts some of this energy deeper into the ground and also heats the air near the surface. This creates a temperature gradient wherein the surface is warmest and the air gets relatively cooler with elevation (remember the red line in the graph above).
As the air near the surface warms, that energy causes air molecules to vibrate and push away from one another. Parcels of air become less dense and rise just like the gloop in a lava lamp. The cooler air around it falls to fill in the space left behind, and air begins to circulate in a Convection Cell. The rising parcel of air will eventually cool and shrink as it rises through the relatively cooler air above it.
These convection cells create Thermal Turbulence, which is a very effective way for airborne particles, such as pesticide vapour, to be rapidly diluted. This is also how the atmosphere disperses pollution. More on the process of dispersion, later.
Mid to late afternoon
As the sun passes over and the wind starts to rise, the convection cells get disrupted by the wind and experience mechanical turbulence (remember the blue line in the graph above). So, mechanical turbulence also mixes warmer air near the ground with cooler air above it, but suppresses thermal turbulence.
Mid-afternoon to night
As the energy from the sun lessens, the soil begins to cool and so does the air next to it. Once the air cools enough to be colder than the air above it, we have the beginning of a Radiation Inversion, which is a specific kind of Thermal Inversion (see the green line in the graph below). It is called that because we now have the reverse of the typical day-time temperature profile. The height of the inversion (the ceiling) grows with time, and can reach a maximum of about 100m by sunrise. Within the inversion layer (before the green line bends back at 100m), turbulence is suppressed. We have a stable air mass. More on that below.
How inversions affect dispersion
The rising portion of a convection cell carries whatever particles are in the air with it. Suspended particles become much less concentrated at ground level thanks to the thermal turbulence.
Thermal Turbulence allows particle-laden warm air to rise and clean cool air to fall. This disperses air-borne particles like dust or pollution.
Now let’s imagine we are in a thermal inversion. The cooler, particle laden air near the ground cannot rise and the cleaner air above, which is now relatively warmer, cannot sink. Thermal turbulence is suppressed, and so is any vertical dispersion.
Thermal Turbulence is suppressed during a Temperature Inversion. Particle-laden cool air at the surface cannot rise, and warm, clean air cannot fall. No dispersion occurs, and the concentrated, particle-laden air tends to move downhill or laterally with light winds.
When spraying, the smallest spray droplets fall slowest, staying airborne for long periods of time. If spraying occurs during an inversion, those particles accumulate beneath the inversion layer. Remember we said our atmosphere behaves like a liquid? The colder, denser (pesticide-laden) air drains downhill into low-lying areas. It can also move laterally over great distances, in unpredictable directions, when light winds begin.
Clouds
If the morning were overcast instead of clear, the clouds would intercept much of the sun’s short-wave radiation, absorbing or reflecting it back into space. The Earth’s surface would still warm, but more slowly, suppressing thermal turbulence. As an aside, if clouds form in the evening, they reflect long-wave radiation from the Earth’s surface back down. This Greenhouse Effect is why overcast nights are warmer than clear ones.
Therefore, extended periods of mostly clear skies in the evening or night means a high probability of strong temperature inversions. Conversely, cloud cover usually means a near-neutral atmosphere, so no strong inversion.
Wind
Inversions are only mildly affected by light wind (e.g. 6 to 8 km/h), but as the wind increases and mechanical turbulence mixes the air, the strength of the inversion will be reduced and the atmosphere will approach a neutral condition (see the blue line). In this condition, airborne particles are not dispersed by thermal turbulence, but some mixing will occur. So, there may not be a thermal inversion, but spraying would still be inadvisable if the wind got too high.
Humidity
Inversions form more rapidly when there is less water vapour in the air to absorb radiation. Once humid air has cooled to the dew point, water condensation gives off energy and warms the air a little. This slows the formation of the inversion. Be aware that inversion conditions can exist long before fog, dew or frost forms, so they are not a good indicator for the beginning of an inversion – you’re already in one!
If you see fog, dew or frost, you’re already in an inversion. The air has become cold enough to condense or even freeze water.
Soil conditions and topography
This is a complex issue, but soil conditions that make inversions more intense include low soil moisture, freshly tilled soils, coarse soils, heavy residue and closed crop canopies. Topography matters, too. We’re discussing radiation inversions in arable regions, and the kind that form on mountains or deep valleys. Nevertheless, inversions in shaded areas (e.g., behind windbreaks) start sooner, and last longer. See the NDSU factsheet for more detail.
Spray timing
Inversions, once formed, persist until the sun rises and warms the Earth’s surface, or until winds increase and mix the stationary layers of air together, re-establishing a more neutral temperature profile.
Sunset is not a good indicator of the beginning of an inversion – it can start a few hours before. Therefore, evening spraying may be just as risky as night spraying. Very early mornings (e.g. around sunrise) are not much better. Remember, at sunrise, the inversion will be at its maximum height.
The rising sun will warm the earth and create turbulent conditions, starting near its surface (e.g. a few metres). Most inversions will have dissipated two hours after sunrise, which may be the best choice for spraying.
Detecting an inversion
The only sure way to know if you are in an inversion is to take two air temperature readings: one near the ground and one about three metres higher. If the surface air temperature is cooler, you are in an inversion. The magnitude of the difference indicates how strong the inversion is.
Accurate measurements are difficult to manage with conventional thermometers, but SpotOn now makes a hand-held detection unit. If you have one, be sure to let it acclimate before you use it. Leaving it in a hot, or cold, truck or sprayer cab prior to use means it may give a false reading.
Inversion forecasting is getting better, but it’s still location-specific and not entirely reliable. Sprayer operators should learn to watch for the following environmental cues:
- Large temperature swings between daytime and the previous night.
- Calm (e.g. less than 3 km/h wind) and clear conditions when the sun is low.
- Intense high pressure systems (usually associated with clear skies) and low humidity where you intend to spray.
- Dew or frost indicating cooler air near the ground (fog may be too late).
- Smoke or dust hanging in the air or moving laterally.
- Odours travelling large distances and seeming more intense.
- Daytime cumulus clouds collapse toward the evening.
- Overnight cloud cover is 25% or less.
Note: If you suspect a temperature inversion, don’t spray.
For more information on how weather affects drift, download this pamphlet from the Australian Government Bureau of Meteorology.
March 26, 2020

Sprayer Loading and the Jar Test

This article was co-written with Mike Cowbrough, OMAFRA Weed Management Specialist – Field Crops

The time and attention spent during sprayer loading is a worthy investment. It ensures that the products in the tank perform as intended and reduces the chance of physical incompatibilities.

The label

Pesticide labels are always the first point of reference. Labelled mixing instructions should be obeyed even if they contradict conventional practices (see Mixing order, below). Consult this article on tank mix compatibility for more information on how to quickly and easily consult labels for each of your tank mix partners.

The carrier

Typically, the carrier is water. Water plays a very important role in tank mixing that is often underappreciated. Take some time to read Les Henry’s 2016 Grainnews article called “The Coles Notes of Water Chemistry“. You can also read about pH and water hardness. It should be noted that pH and the resultant hydrolysis that can affect product half-life is typically an insecticide issue (not fungicide or herbicide). The famous example is Captan, which has a half-life of 32 hours at pH 5, but only 10 minutes at pH 8. Michigan State did a great summary (in 2008 and on US product formulations) which you can find here.

Finally, learn how to read a water quality report, here.

Carrier volume

Products dissolve better in higher volumes. The sprayer tank (vat, inductor, etc.) should be at least ½ full or water before adding the first product. In the case of a fertilizer carrier, it may look like water, but it contains high levels of salts that tie up free water and reduce solubility. For fertilizers, a higher initial volume of ¾ full is required.

The incomplete dissolution of products can leave hard-to-clean residues, plug fluid lines, and result in a non-uniform application that reduces efficacy. The risk of incompatibility is greater with low carrier volumes and high product rates (especially dry formulations). This is a common problem in regions that use low water volumes to apply multiple tank mix partners.

Carrier and product temperature

Both carrier and product temperature affect mixing. Imagine mixing sugar in hot tea versus iced tea – more sugar dissolves more quickly in hot liquid. Here are three common temperature-related issues:

Dry formulations and liquid flowables take more time to disperse (consider using a pre-mixed slurry).
Emulsified concentrates and oil might form gels rather than milky blooms.
Water soluble packages might not dissolve completely and could plug filters and nozzles – or clog the pump intake.

Note the undissolved residue collected on these swatches of red material. Products dissolve faster and better when carrier and products are warmer.

Note: Water and fertilizer are very different carriers. Beware of carrier-specific incompatibilities

Agitation

Agitation should be on-going during mixing and spraying. When agitation is too low, products may not disperse or suspend and can settle out. In the case of leaving a sprayer overnight without agitation, settled product may or may not resuspend. See this article.

When agitation is too aggressive (e.g. full agitation when tank is less than half full) product can foam, causing overflows or breaking pump suction during spraying. Over agitation can also cause dispersed products (e.g. emulsifiable concentrates) to separate and cause clumping that looks like curds.

Note: When agitating, the surface of the carrier should be closer to a simmer than a rolling boil.

Pace

Products may require more than five minutes between additions. This is especially important when carrier or product is cold, or when adding dry products. When products are added too quickly, they will not entirely disperse or suspend, which could result in a physical incompatibility with subsequent additions. Learn more about the importance of time and patience during loading.

While efficient sprayer loading is an excellent opportunity to improve your work rate, complicated tank mixes still require time between additions. To save some time, sprayer operators pre-hydrate dry products in a smaller tank or use an extra tank to pre-mix whole loads and simply transfer them over.

Note: Even when dry products appear to be dissolved, they may not be. Be patient

Product formulation

Product formulation is a complicated science. In the 1950’s a formulation might have three active ingredients and an inert filler. See the historic formulation index card shared by Dr. M Doug Baumann (formally with Syngenta, Honeywood). Today, a product can include ~40 ingredients with formulation testing lasting two to four years! The more products you add to the tank, the higher the risk of antagonism.

Note: If you experience physical incompatibility during loading, don’t blame the last product you put in the tank!

Mixing order

The order in which you add tank mix partners is critical. There are several acronyms around to help you decide on your mixing order. Here are the top three:

W.A.L.E.S. (Wettable powders, Agitate, Liquid flowables, Emulsifiable concentrates, Surfactants).
BASF’s W.A.M.L.E.G.S. (Wettable powders, Agitate, Microencapsulated suspensions Liquid flowables, Emulsifiable concentrates, high-load Glyphosates, Surfactants)
A.P.P.L.E.S. (Agitate, Powders soluble, Powders dry, Liquid flowables and suspensions, Emulsifiable concentrates, Solutions)

W.A.L.E.S. is not broken. In fact, formulation chemists expect it to work ~95% of time. Generally, soluble liquids are forgiving and can be added early or late. It’s the dry formulations and emulsifiable concentrates that require more care. When there are exceptions to the order, they are clearly indicated on the pesticide label.

W.A.L.E.S. is, perhaps, a bit simplistic. Products that fall within each “letter” have their own preferred mixing order that isn’t specified by the acronym. What follows is an expanded generic mixing order.

Water-Soluble Bags (WSB) – Allow them to fully dissolve and disperse.
Wettable Powders (WP)
Water Dispersible Granules (WDG, WG, SG)
Agitation to allow dry products to mix and disperse.
Liquid Flowables (F, FL): Including, in order, Suspension Concentrates (SC), Suspo-emulsions (SE), Capsule Suspensions (CS/ZC), Dispersible Concentrates (DC), Emulsions in water (EW).
In order: Emulsifiable Concentrates (EC): Microemulsifiable Concentrates (MEC) and Oil Dispersions (OD).
In order: Solutions (SN), Soluble Liquids (SL), Liquid Fertilizers and Micronurients (when not already premixed with fertilizer).
NOTE: Regarding adjuvants, always follow the label. If the label is silent, most water conditioning utility modifiers (e.g. compatibility agents, anti-foamers) should be added before pesticides. However, drift retardant utility modifiers are added dead last. Activator adjuvants like Non-Ionic Surfactants (NIS) and Crop Oil Concentrates (COC) tend to be added after pesticides, but are sometimes added based on their formulation, falling into order just like pesticides. Again, read the label.

An example

Micronutrients like sulfur (e.g. ATS) added to nitrogen-based formulations (e.g. UAN) can cause physical incompatibilities. This became a problem during “weed-and-feed” applications in Ontario corn, and thanks to the efforts of the pesticide manufacturer, we worked out a solution.

What follows is not only a good example of why mixing order is critical, but why growers should get into the habit of performing jar tests. Learn more about a real-world ATS example here.

**Left:** ATS and UAN premixed, followed by Primextra created curds.
**Centre:** UAN, followed by low-load ATS followed by Primextra worked.
**Right:** UAN followed by Primextra followed by high-load ATS worked.

Small-plot mixing order

Mixing errors are just as likely in small plot work as in commercial sprayers. Watch this short video case study describing mixing order for Elevore and glyphosate.

The jar test

Performing a jar test is like filling a sprayer in miniature. Follow all the same rules as filling your sprayer. Always wear personal protective equipment when performing a jar test. Do so in a safe and ventilated area, away from sources of ignition.

Read all product labels. Know the product formulation (which affects mixing method and order). Look for information about the influence of carrier pH, hardness and any requirement for adjuvants. Defer to label instructions should they differ from these mixing steps.
Shake any liquid products. This ensures the active ingredient and inert ingredients are thoroughly mixed.
If using water as a carrier, add 250 ml to a 1 litre glass jar. For oil or fertilizer, add 375 ml.
Agitate (stir) between additions. In a sprayer, agitation should continue throughout the mixing process.
Add products in order (see Mixing order, above). Scale back the weights/volumes used to match the concentration intended for an actual sprayer tank (e.g. 1 kg product in a 1,000 litre sprayer tank is 0.5 g product in a 500 ml jar test). In a sprayer, you would flush an inductor with water between additions.
Wait and check. Dry products and water-soluble packets must fully disperse and/or dissolve before adding the next product. Several factors affect the duration, but 3-5 minutes is typical. If testing water-soluble packets, include a ~1cm² cutting of the PVA packaging.
Top up the carrier to 500 ml.
Measure pH using a digital meter (litmus papers may not be readable). This is best done after all products are added to account for their impact on pH and buffering capacity. If required, pH adjusters can be added at the end of mixing to ensure the solution is in the range required by the label.
Let the solution stand in a ventilated area for 15 minutes and observe the results. If the mixture is giving off heat, these ingredients are not compatible. If gel or scum forms or solids settle to the bottom (except for the wettable powders) then the mixture is likely not compatible.

Note: jar test will only reveal physical incompatibility between products – it will not reveal any other form of antagonism.

Compatibility kits

When performing a jar test you must maintain the same product-to-carrier ratio as in a full-sized sprayer tank. This math is made easier with commercial compatibility kits such as the one from Precision Laboratories (below).

Compatibility Test Kit: Five pipettes, three bottles, gloves, instructions. ~$10.00. (Photo: Precision Laboratories)

Such kits contain a few plastic “jars” and disposable micropipettes. By following the instructions included with the kit, you can easily reduce large labelled volumes (e.g. 1 kg of product in 1,000 litres) of multiple products to small volumes at the same ratio. In this case we assume the final volume would have been 1,000 L, and so we reduce all the quantities accordingly to get 500 ml. The following mixing order is provided as an example.

Order	Ingredient	Quantity for 500 ml or 500 g of product labeled for 1,000 L of final spray volume
1	Compatibility agents	5 ml (1 teaspoon)
2	Water soluble packets, wettable powders and dry flowables. Include a 1cm2 cutting of PVA packaging.	15 g (1 tablespoon)
3	Liquid drift retardants	5 ml (1 teaspoon)
4	Liquid concentrates, micro-emulsions and suspension concentrates	5 ml (1 teaspoon)
5	Emulsifiable concentrates	5 ml (1 teaspoon)
6	Water-soluble concentrates or solutions	5 ml (1 teaspoon)
7	Remaining adjuvants and surfactants	5 ml (1 teaspoon)

Records and delayed reactions

Keep detailed records of what you mixed and how you mixed it. This is important for traceability (e.g. CanadaGAP) and for tracking successes and failures for next year.

The jar test itself can become a valuable record if it’s labelled and left in the chemical shed. You will see if products separate, precipitate or form residues. This may indicate if you can let a tank mix sit overnight or if it will require special attention during rinsing.

For example, a grower tank-mixed Enlist with Manzinphos, which seemed to mix and spray with no issues until they were rained out and had to park the sprayer with 100 gallons of tank mix still in the system. The mixture turned to “lard”, plugging up all of the lines, filters, and the pump. They had no choice but to disassemble the sprayer and dig some of the substance out with screwdrivers (see the picture of the filter below). Perhaps if they had run a jar test and left the jar overnight this problem could have been avoided.

Some physical incompatibilities are not immediately apparent. This occurred overnight while the partially-full sprayer waited out a rain event.

Closed transfer

As a brief mention, an expansion of closed transfers systems for loading pesticides is on the horizon in North America. Manufacturers of these systems claim they will make loading more efficient, reduce operator exposure and reduce point-source contamination. Depending on the design, however, the operator may not be able to open pesticide containers to obtain samples for jar testing. This would be a great loss.

For more information

Learn more about physical and chemical incompatibility in our article on Tank mix compatibility. Be sure to download a copy of Purdue University’s 2018 “Avoid Tank Mixing Errors”. It is an excellent reference.

February 4, 2020

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.
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.
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.
January 2, 2020
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.
September 24, 2019
Biobeds for Pesticide Waste Disposal
One of the most challenging aspects of a spray operation is the disposal of leftovers or rinsate containing pesticides. Let’s be honest, too much of it is drained onto the ground in a corner of the yard or the field. Nobody’s happy about that, nobody’s proud of it, but what are the alternatives?
Waste disposal is a skeleton in the closet of the pesticide industry. One of the problems is the time-consuming nature of sprayer cleaning, and the lack of clear guidelines on product labels that pass the buck. Too often, the applicator is asked to “act in accordance with provincial or state guidelines”, which is essentially a dead end.
Figure 1: Sprayer fill station
At Sprayers101.com, we’ve tried to tackle the problem by finding ways to generate less waste (Express End Caps, Accu-Volume), by disposing of the rinsate by spraying it out, or by installing an efficient continuous rinsing system. We’d now like to talk about another component, biobeds.
What is a biobed?
Simply put, a biobed is a place where it’s safe and acceptable to dump dilute pesticide waste. First implemented in Sweden about 20 years ago, a biobed typically consists of a 1-m deep pit measuring about 3 m x 6 m or so. The pit is filled with a biomix, a mixture of cereal straw, compost or peat, and soil. The biomix, when properly prepared, acts to absorb a large amount of moisture, adsorb the pesticide molecules, and provide an environment in which microbes break down the residues.
Figure 2: Canada’s first commercial biobed installation at Indian Head, SK, 2009 (Source: Murray Belyk, Bayer CropScience (retired)).
The effluent from a properly constructed biobed system contains 90 to 99% less pesticide than what was introduced, depending on the pesticide.
Biobeds have been extensively studied and are now found throughout Europe and many parts of Central and South America. Canada currently has 6 research biobed sites in the West, and a further 17 in Quebec. The systems have been researched by Agriculture & Agri-Food Canada (AAFC) in recent years, with promising results.
Figure 3: European biobed installations, 2016 (Source: Jens Husby, Biobeds.org).
Figure 4: Global biobed installations, 2016 (Source: Jens Husby, Biobeds.org).
Constructing a biobed
There are many possible variations of biobeds, some relatively simple and others engineered to address certain specific needs. A great deal of creativity can be used to customize a biobed for any operation.
A simple biobed
The following is a variation of the simplest biobeds, and these are the types first tested by AAFC in Saskatoon and Indian Head, Saskatchewan about 10 years ago. This design is based on the biobeds established in Sweden and the UK, and is a good way to learn about the system.
Note that this biobed has an impermeable liner, so it’s a closed system. Excess water that leaches to the bottom must be removed and cycled back to the top of the biobed.
- Create the biomix by blending two parts, by volume, chopped cereal straw or wood chips (not cedar), one part mature plant-sourced compost or peat and one part relatively coarse-textured soil (for optimal drainage). Add water as necessary as if making compost. Allow to sit for four to six weeks.
Figure 5: Biomix preparation.
- During this waiting time, the biomix will warm and form a white-mold complex. This is the microbial basis for its ability to break down pesticide residues. White mold will be visible on the cellulose portions of the biomix.
Figure 6: white mold (Source: AAFC).
- Identify a well-drained site easily accessible by spray equipment. Avoid low spots as water management becomes problematic.
Figure 7: Site selection and/or biobed covering are essential to avoid waterlogging (Source: Murray Belyk, Bayer CropScience (retired)).
- Dig a pit sized to suit your requirements. As a rule of thumb, 1 m³ can process about 1000 L of liquid in a season. Rainfall is included in this amount.
Figure 8: A nice looking pit.
- Line the pit with a geomembrane liner. 40 mil is plenty thick; any thicker and it gets hard to handle. Include a raised berm at the edge.
Figure 9: Liner creates a closed system that will require a way to remove leached water.
- Install weeping tile at bottom of pit, and extend it to ground level. This will be useful to determine water status and remove water if necessary.
Figure 10: Weeping tile to collect excess water.
- Cover weeping tile with pea gravel and a silt trap. This serves to make leached water freely available for removal.
Figure 11: Pea gravel over weeping tile.
- Fill pit with biomix, anticipating significant settling. Top up as necessary over next few weeks. Use extra biomix to create a slope away from berm.
Figure 12: Filled biobed.
- Establish a bromegrass cover by transplanting or sodding. This is an important way to remove excess water via evapotranspiration.
Figure 13: Early sod growth on biobed at Indian Head, SK.
- Introduce pesticide waste to biobed, managing moisture content to avoid waterlogging.
Figure 14: Pesticide waste entering biobed via drip irrigation.
Introduction of pesticide waste to the biobed
Moving pesticide waste from the sprayer to the biobed should be easy and trouble free. A simple pad built beside biobeds, either sealed with concrete or asphalt, or with a hardy geomembrane liner, works well. The sprayer is cleaned on this pad and rinsate flows into a drain. A sump pump lifts the rinsate to a storage tank from which it is introduced via gravity or pumped drip irrigation.
Figure 15: Biobed system in Simpson, SK. Rinsate from sprayer is collected in a sump, which is pumped to the black storage tank in background. Rinsate is introduced into biobed (blue tub) as needed (Brian Caldwell in foreground, left, Larry Braul, right).
When not in use, the sump drains freely to dispose of rain water.
Others choose to pump or dump rinsate directly into a holding tank, from where it can be pumped onto the biobed.
Figure 16: Holding tank at biobed in Outlook, SK.
Some European systems include driving supports on the biobed so the sprayer can be parked directly over top.
Figure 17: Steel beams can allow (light) sprayer access (Source: Eskil Nilsson via Biobeds.org).
A two-stage biobed
The same basic building principles apply as in the original simple biobed. However, instead of reintroducing the effluent to the top of the biomix as it collects on the bottom, it is instead pumped onto a second biobed. This biobed then degrades any remaining product. This system is more efficient at degrading persistent products, and allows for better water management.
Figure 18: Two-stage biobed system at Outlook, SK.
The principle has proven effective, helping degrade more difficult pesticides to acceptable levels.
Above-ground biobeds
One of the problems with below-ground biobeds in wet climates is the difficulty managing water. Above-ground biobeds can address this issue by eliminating the possibility of surface runoff being added to the biomix. Adding a rain cover would also be easier and more effective.
Above-ground biobeds can be edged with plywood, or placed entirely into plastic tanks whose tops have been removed.
Figure 19: Above ground biobed installation with plastic tub.
One potential problem with above-ground biobeds is the later spring warming of this installation compared to below-ground types. Cold temperature reduces the effectiveness of biobeds due to the reliance on microbial activity. Heat tape has been tested by AAFC and shown to be very effective at warming the biomix and stimulating initial microbial activity. Passive solar systems have also been studied but are more difficult to install.
Figure 20: Heat tape (Source: AAFC).
Figure 21: Passive solar biomix heating system.
Phytobac and Biofilters
European designs have utilized plastic containers to form of various designs, including the commercial “Phytobac” systems from France and developed with the support of Bayer CropScience.
Sequential biofilters have also been implemented. The leachate simply migrates through the biomix into the next container below. Eventually, adjacent biofilters containing plants act to remove the moisture.
Figure 22: Phytobac installation, cross-section.
Figure 23: Biofilter installation in Belgium (Source: Inge Mestdagh via Biobeds.org).
Biomix longevity
Swedish and UK research has suggested that biobeds require minimal maintenance aside from water management in closed systems. Biomix will settle over time and may need to be topped up. After five to eight years of use, it has been recommended to remove biomix and distribute it over a field with a manure spreader.
Canadian research results
Extensive analysis of pesticide degradation in five biobeds across Western Canada was conducted as part of a three-year study led by AAFC. Between eight and 51 products were analyzed per site, including herbicides, fungicides, and insecticides. Their results showed that single biobeds could remove about 90% of the introduced pesticide, and two in sequence usually removed more than 98%.
Pesticides that tended not to degrade rapidly were removed to a greater degree in the second biobed.
In the AAFC studies, three herbicides were more difficult to remove in the tested biobeds: clopyralid (e.g., Lontrel, Stinger), bentazon (Basagran, Storm) and imazethapyr (Pursuit, Arsenal). For these three, roughly 60% was removed in a two-biobed system.
Concentrated pesticides should not be introduced to a biobed as this will kill the microbial populations.
Some fungicides were shown to depress microbial populations but only temporarily. Microbial breakdown still occurred.
Biobed manual
AAFC has authored a comprehensive manual on biobed operation and installation based on research experience in Canada and elsewhere. It will be available here in late June 2018.
The future of biobeds
Research into biobeds remains active around the world. Different substrates for the biomix are being studied to suit local availabilities. Various systems, ranging from simple to highly engineered are being studied. Degradation effectiveness for various influents remains a topic of significant interest. Producer adoption and implementation are being reported.
Thanks to funded research projects, biobeds are up and working at Canadian institutional sites such as government research centres, and there are opportunities for county and municipal government sites. For biobeds to be a viable option on North American farms, their design needs to remain simple and their integration into established practices needs to be seamless. Producer experience and feedback are essential
Learn more
Valuable information on biobeds can be obtained from these two websites:
Voluntary Initiative (UK industry)
Biobeds.org (International research)
Note: Brian Caldwell and I first learned about biobeds from Eskil Nilsson (website) during a visit to Sweden in 2001, and obtained support for initial studies in Saskatoon and Indian Head from the Pest Management Centre as well as Bayer CropScience. Brian took a lead in our creative and technical efforts over many years. Dean Ngombe, under the co-supervision of Diane Knight at the U of S and myself, produced the first M.Sc. thesis, and with significant input from Allan Cessna, the first scientific publications in Canada on biobeds. Thanks for Larry Braul and many collaborators for leading the most recent AAFC study and generously sharing resources, and Erl Svendsen, Bruce Gossen, and Claudia Sheedy for editorial input.
May 20, 2018