Tag: pesticide

  • Ten Tips for Spraying in the Wind

    Ten Tips for Spraying in the Wind

    Choosing the right time to spray can be tricky. Our gut tells us that spraying when it’s windy is wrong.  The experts tell us that spraying when it’s calm is wrong. So when can you actually spray?

    I’ve always advised my clients to spray in some wind, because it has a few advantages. The main one is that wind helps disperse the spray upward and downward, diluting the spray cloud fairly rapidly. Another advantage is that winds tend to be reasonably steady in their direction and velocity (or at least that can be forecast), so downwind areas can be identified and potential impacts are known or predictable. It helps if it’s sunny, because that improves the dispersion of the cloud even more.

    First, let’s define “windy”. The classic wind scale is the Beaufort Scale, intended for the sea, but also used on land. The upper limit for spraying is probably Force 3 or Force 4, with upper limits of 20 – 25 km/h or so.  The Beaufort Scale calls these “Gentle or Moderate Breezes” (they had to save the alarming words for hurricanes), and the scale provides good visual clues such as what wind does to flags, leaves, or dust.

    Beaufort Scale-1

    Spraying under breezy conditions can be done fairly safely if you follow specific steps. The idea is to understand what the risks are and to manage them.

    The cornerstone is to use a low-drift spray and match it to a pesticide that will work well with larger droplets. But there are other important aspects to consider. Below are the top ten to think about:

    • Choose a herbicide that can handle large droplets. Glyphosate products are well suited to coarse droplets. But glyphosate commonly has contact actives in the mix, members of Group 6, 14, and 15, and these are less likely to perform well with big droplets than those that contain Group 2 and 4 mixes. Actives with soil activity also have more tolerance for larger droplets.
    • Use a low-drift nozzle and operate it so it produces a Coarse (C) to Very Coarse (VC) spray quality, as described by the manufacturer. Dicamba labels call for Extremely Coarse (XC) to Ultra-Coarse (UC) sprays, and Enlist requires at least Coarse. To achieve these you may need to purchase new nozzles. Low-pressure air-induced nozzles operated at about 50 – 60 psi will generally be very low-drift, but lower drift models are available. If you need a finer spray, produce it either by increasing the pressure or moving to a finer tip. Do this when the weather improves, for contact modes of action.
    The name, symbol and range of droplet sizes used to describe the median droplet diameter produced by nozzles according to ASABE S572.3
    • Keep your boom low. Lowering the boom ranks as the second-most effective way to reduce drift, after coarser sprays. But there’s a limit. For low-drift sprays, you need at least 100% overlap (more for PWM), which is for the edge of one nozzle pattern to spray into the centre of the adjacent pattern. In other words, the spray pattern should be twice as wide as your nozzle spacing at target height.  For most nozzles, a boom height of close to 20 inches is enough to achieve this overlap. That’s pretty low by current standards from suspended booms on self-propelled sprayers, so being too low for a good pattern will only happen due to boom sway.
    • Maintain reasonably slow travel speeds. These reduce the amount of fine droplets that hang behind the spray boom, reduce turbulence from sprayer wheels, and they also make low booms more practical. An added bonus is less dust generation.
    • Know what’s downwind and what harms it. Survey the fields on all sides of the parcel you’re treating. When you have a choice, avoid spraying fields that have sensitive areas downwind such as water, shelterbelts, pastures, people, etc. If you can’t avoid being upwind of these areas, make sure you check and obey the buffer zone restrictions on the label. These will also give you an idea if the product can cause harm in water or on land, or both.
    • Consider a dicamba tip for special situations, even if you don’t use dicamba. If you’re in a situation where quitting and waiting is a poor option, these tips allow you to finish the job with minimal drift risk and with only slight reductions in product performance due to poor coverage.
    • Use a low-drift adjuvant. Specific products such as Interlock or Valid have been shown to reduce driftable fines (<150 microns) by between 40 – 60%, without adding significant volume in coarser droplets. The response will depend on the nozzle and the tank mix, but can be very noticeable.
    • Study drift and how it forms and moves. It’s about more than wind speed and droplet size. Knowledge in this area can help you work out the best strategies.
    • Invest in productivity. You may not need it every day, but on occasions when you have a small window to avoid bad weather, it pays dividends.
    • If you feel that drift is unavoidable and someone might be impacted by it, talk to those people first. It’s one of the most important things you can do.

    Keeping pesticide sprays on target continues to be one of our top responsibilities.

  • Pesticide Safety for Student Workers

    Pesticide Safety for Student Workers

    This article is based on a presentation by Dr. Melanie Filotas, who delivered it as part of the 2019 agriculture summer student orientation day.

    Most crops are sprayed with organic or synthetic pesticides at some point during the growing season. Use caution before entering any area where crops are grown (e.g. corn field, nursery, greenhouse, orchard etc.). Always confirm that it is safe to enter.

    Most crops receive some form of chemical input during growth. Be aware of what has been applied.
    Even organic operations apply controlled products that may make it unsafe to enter for a period of time.

    You can be exposed to pesticides if you enter a treated area before pesticide residues break down and vapours dissipate. The minimal time that must elapse before being permitted to enter is called the Restricted Entry or Re-entry Interval (REI).

    REIs are data-driven and established by the federal government. They are defined as: “The period of time that agricultural workers, or anyone else, must not do hand labour in treated areas after a pesticide has been applied.” Hand labour can be any task involving substantial contact with treated plants, plant parts or soil, including planting, harvesting, pruning, and scouting.

    Things you should know about REIs:

    • REIs can range from one hour to several days
    • If a pesticide label does not indicate a REI, the default is 12 hours
    • REIs can vary with the product, crop and type of activity (e.g., scouting, harvesting, etc.)
    • REIs can change over time so always refer to the most recent label
    • If a tank mix (multiple products) was applied, observe the most restrictive REI

    Before visiting an operation to work in the field:

    • Tell your supervisor where you will be that day
    • Ask the grower or spray applicator what was sprayed. Records may be posted, but verbal confirmation is preferred
    • Look up the REI for the product on the crop you will be entering
    • Check with your supervisor on any products with special instructions beyond the REI

    Do not enter the field until the REI has ended. Pesticide REIs can be found in local production guides, or on pesticide labels.

    Local production guides summarize REIs.
    Local production guides list REIs by crop, by product applied, and by activity.

    If local production guides are not available, registered pesticide labels can be found using Health Canada’s Pesticide Label Search service online. In the United States, most labels can be found on the EPA’s Pesticide Product and Label System website.

    Health Canada’s online pesticide label search.

    Miscommunication can sometimes happen. Learn to recognize the signs of spraying. When in doubt, leave the planted area and call the grower to confirm or call your supervisor.

    • In some cases you can look for fresh tracks in the operation, but be aware they may not have been made by a sprayer
    • Some products have a distinctive odour
    • It can be difficult to see a sprayer operating, particularly in orchards, but they can be heard. Do not wear earbuds or headsets while in a production area
    • Look for foliar residue. This is an indicator, but does not always mean it is unsafe to enter
    Fresh wheel tracks may indicate recent spraying.
    Some products have a distinctive odour.
    It may be difficult to see a sprayer operating in the vicinity, such as in this orchard. However, they can often be heard. Do not wear a headset or earbuds in a production area.
    Residue on leaves may indicate a recent application, as in the left photo. However, it could also be unrelated. On the right is calcium magnesium precipitation from irrigation water. (Photo credit [right]: Jennifer Llewellyn)

    There are many potential symptoms of pesticide exposure: headache, fatigue, irritation of the skin, eyes, nose or throat, loss of appetite, dizziness, nausea or vomiting, diarrhea, decreased muscle coordination, and blurred vision. Each product has a Material Safety Data Sheet (MSDS) that will provide details on exposure symptoms and treatments.

    While sometimes confused with symptoms arising from sun stroke or dehydration, if you suspect pesticide exposure it is always best to be prudent and get medical help immediately. Contact your local poison centre or 911.

    Summer work in crop production can be rewarding and enjoyable, but always use caution and be safe.

  • Thermal Inversions for Sprayer Operators

    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 the landscape is not. Our focus in on the Surface Boundary Layer.
    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.
    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.

  • 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.

  • 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.