Before You Spray

Tacy Callies CEU

Take proper precautions when preparing to spray.

By Matt Smith

Editor’s note: This article grants one continuing education unit (CEU) in the Core category toward the renewal of a Florida Department of Agriculture and Consumer Services restricted-use pesticide license when the accompanying test is submitted and approved.

We often think about pesticide safety and best management practices when we are in the field spraying. You’re outside, you’re potentially exposed to the pesticide, and a gust of wind in the wrong direction could send it flying back into your face. However, your first interaction with pesticides on spray day takes place well before you step foot in the field.

There are several things you can do before spraying to help ensure a safe and efficient application. This article will cover a few of them, including identifying the target pest, ensuring your pesticide label is up to date, calibrating equipment, wearing the proper personal protective equipment (PPE) during mixing and loading, and testing product compatibility.

The first step in a proper integrated pest management strategy is to identify the target pest.

Did you ever see Point Break? In this movie, Keanu Reeves plays Johnny Utah, a Federal Bureau of Investigation (FBI) agent tasked with identifying, infiltrating and dismantling a gang of surfing bank robbers. Special Agent Utah makes the critical mistake of not correctly identifying the target pest. Instead, on an uninformed instinct, he authorizes a raid of an unrelated group of surfers led by the lead singer of the Red Hot Chili Peppers that, while certainly pests, had not met the threshold to control and were under observation. The botched raid cost the FBI time and manpower while destroying a multi-year Food and Drug Administration investigation. Meanwhile, the actual target pests — led by Patrick Swayze as the iconic Bodhi — continued to do considerable damage until they were finally properly identified and controlled.

There is no magic bullet pesticide that kills every pest and spares every crop. To properly control pests in the field, proper identification of pests is needed to select the correct product to treat them with.

While the label is the law, the label is not always consistent. This is especially true with pesticides that have been approved under a Section 18 emergency-use authorization. When a new pest strikes an area where no pesticides are registered, a state regulatory body can lobby the Environmental Protection Agency (EPA) to authorize applicators to use pesticides that may control the new target pest but are not labeled for that use.

If granted, the state pesticide regulatory agency, the Florida Department of Agriculture and Consumer Services (FDACS) in Florida’s case, prescribes application rates, safety precautions and other information for applicator and environmental safety. While Section 18 authorizations resemble normal pesticide labels, they are not technically labels or labeling because the product has not been registered with the EPA.

Section 18 emergency exemptions authorize pesticides for a limited time and special use. However, a pesticide authorized under a Section 18 exemption may be granted a Section 3 (normal) registration and become authorized for normal use. When this happens, the rules and regulations for applying the pesticide may change. A recent example of this is FireWall 50 WP.

FireWall 50 WP, developed by AgroSource, is a streptomycin-based bactericide/fungicide which was granted an EPA Section 18 emergency exemption several years ago to suppress HLB in Florida citrus and to aid in controlling citrus canker in Florida grapefruit. FireWall 50 WP received a Section 3 label on April 23, 2021. The application rules are nearly the same in the Section 3 label as the old Section 18 exemption, except that the preharvest interval has increased from 40 to 60 days. This change is especially important for growers planning to apply FireWall 50 WP close to harvest. It is also a good reminder to ensure you are up to date on changes to your pesticide’s label.

Calibrating equipment is something very few people like to do and is often the most challenging part of the pesticide exam. However, it is a critical step in proper pesticide application. Calibration is the process of learning and adjusting your equipment’s output rate to ensure you are applying an even and accurate dosage.

A properly calibrated sprayer saves time and money. If, for example, a sprayer is producing more output than it should, plants will receive excessive chemicals that may cause phytotoxicity. The applicator will have to make more return trips to the mixing-loading station, costing both time and money in the form of excess chemical concentrate. An excessive application may also change the pesticide exposure levels for applicators and workers.

You can spray with confidence once you’ve calibrated your equipment. However, do not assume that a calibrated sprayer will remain calibrated forever. Several factors, including nozzle wear, the buildup of deposits in liquid lines or even accidental changes to the flow-rate controls, can cause the system to no longer operate at peak efficiency. You don’t necessarily need to recalibrate your equipment before every spray, or even every week, but setting up a calibration schedule will help ensure an efficient and safe growing operation.

The mixing and loading stage of pesticide application can be just as hazardous as the application stage, if not more so. During mixing and loading, the pesticide is being handled at its full concentrated strength. As such, any contact with the pesticide may be more hazardous than during spraying when the pesticide is diluted. This contact includes potentially breathing in fumes.

When it is deemed necessary, the label will direct you to wear more PPE during mixing and loading than application. In other circumstances, the label may require less or the same amount of PPE. There is no hard and fast rule, which is why it is important to consult the pesticide label.

Figure 1. A sample pesticide label shows different personal protective equipment requirements for applicators and mixers/loaders.

In the example shown in Figure 1, both applicators and mixers/loaders are required to wear long-sleeved shirts and long pants, waterproof gloves, and shoes and socks. But if you are mixing or loading, you must also wear protective eyewear. A common requirement for mixers/loaders but not applicators is a chemically resistant apron. It is critically important that you treat pesticides with the same amount of respect in the mixing and loading area as when spraying in the field.

How you mix and load is also very important when it comes to pesticide safety. Chemicals should always be mixed below face level to reduce splashing and potential injury.

Like when dealing with acids, always fill your spray tank with water halfway before adding chemicals. You have the greatest risk of splashing when you first apply high-pressure water to an empty tank. If you have pesticide concentrate in an otherwise empty tank and add water from a hose, the first drops that splash out will be highly concentrated with chemicals. To ensure the chemicals in a splashing solution are diluted and less hazardous, add water first, then chemicals, and finish by filling the rest of the tank with water. Always leave an air gap between the hose and the water in the spray tank to prevent the pesticide solution from backflowing into the water supply.

You may want to mix multiple chemicals like pesticides and fertilizers in your sprayer for time-efficient applications. There is no federal prohibition against this unless specified by the label. However, you need to make sure the pesticides and fertilizers you are mixing are physically and chemically compatible. Many pesticide labels have information about tank mixing, but others do not. While chemical compatibility can ultimately only be determined by spraying a test section, you can make sure the mixture is physically compatible with a jar test.

Add each product to the jar in the ratio and order that you will add them to the spray tank. Use the W-A-L-E-S sequence when tank-mixing herbicides:

  1. Wettable powders or water-dispersible granules
  2. Agitate then add adjuvants such as anti-foaming compounds and buffers
  3. Liquids (flowable liquids)
  4. Emulsifiable concentrates
  5. Surfactants

Jar tests are an inexpensive way to test physical compatibility. If the products are not physically compatible, they may form a sludge that can block and damage your spray system. There are two stable liquids shown in Figure 2. The white liquid forms solids that sink to the bottom without constant agitation while mixing. Unlike certain pesticide formulations that are designed to not go into the solution but still pass through a pesticide application system, these solids can wreak havoc on your system and prevent the pesticide from being applied correctly.

Figure 2. This jar test demonstrates physical incompatibility.

There are two kinds of people in this world: 1) People who always use a jar test when tank mixing chemicals for the first time and 2) people who will in the future after they spend three days cleaning 200 gallons of toxic sludge out of their spray system. Should a sludge develop, those cleaning the system must wear full PPE at all times and dispose of the mixture as hazardous waste.

Jar tests can also be used to measure chemical compatibility, though the results are not as easy to spot. The most obvious sign would be something unexpected happening, such as a color change that doesn’t seem intuitive. In Figure 3, a yellow liquid is mixed with a milky white liquid. One may guess that the resulting liquid would be a pale yellow, but instead, it has turned to deep purple. This is a sign of chemical incompatibility. Ultimately, the best way to test chemical incompatibility is to spray a test section of your crop to ensure that plant damage does not occur.

Some products may not form a perfect solution but can still work if there is constant agitation. A tank agitator does this by distributing non-soluble chemicals evenly throughout the tank. If operating a backpack sprayer, the tank agitator is you.

Figure 3. Chemical incompatibility is shown in this jar test.

When we think about pesticide safety and best management practices, we often think of actions we can take in the field while spraying. However, there are steps that take place before spraying that affect the overall safety and efficiency of the operation. Wear the right PPE at all stages, be sure your pesticide labels are up to date, keep equipment calibrated, test compatibility when mixing products for the first time, and try not to be like Johnny Utah.

Acknowledgment: Thanks to Megan Dewdney, associate professor of plant pathology and Extension specialist at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center, for spotting and informing me of the change in the preharvest interval for FireWall 50 WP.

Sources: Applying Pesticides Correctly, 7th Edition by F. Fishel ( and Personal Protective Equipment for Handling Pesticides by F. Fishel (  

IMPORTANT NOTE: If you have questions regarding this form, test or CEUs, email Matt Smith at or call 352-569-6862. Please allow two weeks to process your CEU request.

Matt Smith is a UF/IFAS Extension sustainable agriculture and food systems agent in Bushnell.

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