Key Terms to Know When Using Pesticides

Josh McGillCEU, Pesticides

By Ajia Paolillo

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.


As a certified restricted-use pesticide applicator, it is your responsibility to use pesticides safely, not only for yourself but for others around you and the environment. This article will explain key terms that all pesticide applicators should know and understand when using pesticides.

When most people hear the word pesticide, they usually associate it only with killing bugs. That, of course, is not entirely true. Think of “pesticide” as the umbrella term, describing a group of products used to kill “pests.”

Well, what is a pest? Pests are insects and other arthropods, weeds, diseases or animals that compete with plants, humans or other animals for food and water. These pests can also cause damage or be considered a nuisance.

Under that pesticide umbrella, there are insecticides that control most insects and other arthropods. Herbicides are used to manage weeds in various environments. Fungicides and bactericides target two groups of disease-causing organisms. Rodenticides target animals, including rats and mice.  

Pesticides can be either systemic or contact.

Systemic pesticides work within the plant to manage pests. The pesticide is taken up by the plant, typically through the root system, and is translocated throughout the plant by the vascular system. Systemic insecticides are most effective for insects with piercing-sucking mouthparts that feed on phloem or xylem sap. Some systemic insecticides may provide control of insects that feed on other plant tissues, though. Systemic herbicides kill the weed from the inside out through various mechanisms. Systemic pesticides take longer to be absorbed into the plant, but they usually provide longer-lasting residual control.

On the other hand, contact pesticides work by application to the plant surface or insect’s body. The pesticide must contact the target pest to achieve effective control. Contact herbicides kill plant cells in the immediate covered area. The herbicide does not move within the plant, resulting in a burn-down effect that does not completely eradicate the weed. Although pests are controlled quickly with contact pesticides, they do not typically provide long-lasting residual control.   

Each pesticide contains one or more active ingredients that attack and kill pests. The active ingredient is listed on the product label using the common and chemical name. The active ingredient is the main chemical in the product that kills the pest using a unique mechanism. This mechanism could be a nerve disruptor for insects or a chlorophyll inhibitor for weeds. This mechanism is known as the mode of action. Pesticides are classified into chemical groups based on their active ingredient(s) and mode(s) of action. The product is assigned a group number displayed on the label.

It is crucial for applicators to rotate products with different active ingredients used on the same pests in order to rotate the mode of action. Rotating the mode of action decreases the chance of pesticide resistance. Resistance occurs when the pesticide is no longer effective in controlling the pest.

For instance, if the same mode of action is used back-to-back and not rotated with products that utilize different modes of action, eventually some insects will survive and produce resistant offspring. As the resistant population grows and multiplies, the pesticide no longer effectively controls that population of insects. By rotating products with different modes of action, these products can continue to provide effective control of the pest population.

Pesticide products contain active ingredients and inert ingredients such as fillers, carriers and solvents. Formulation refers to the combination of all ingredients in the pesticide and the form in which that pesticide is available. The formulation is listed on the label and indicates the pesticide’s form: liquid, dust, granular or other. An applicator can choose which formulation is most appropriate for controlling the pest considering the available application equipment. Most formulations are concentrated and must be diluted with water or another carrier.

Adjuvants are products used to enhance the performance of pesticides. Some examples of adjuvants are surfactants that decrease the pesticide droplet’s surface tension, enabling the chemical to cover a larger surface once applied.

The pesticide label provides the applicator with all the information they need regarding the product. The label is attached to the chemical container and should always be legible and available to the applicator. Understanding the pesticide label is essential for every pesticide applicator.

As mentioned above, the product label lists the type of pesticide, chemical group number, formulation, active and inert ingredients. The label also lists application rates, covered commodities and site information.

Before purchasing or applying a pesticide, the applicator should read the label to be familiar with the product and its requirements. The label is the law and must be followed accordingly.

The brand (trade) name is listed in large letters and is the name the manufacturer gives their product. Be advised that products containing the same active ingredient can be manufactured and sold under different brand names.

The product’s signal word is also listed on the label. This indicates the acute toxicity of the product. Signal words include caution, warning, danger and danger-poison.

The label contains directions for use, including required personal protective equipment (PPE) forapplicators, loaders, mixers and early-entry workers. PPE is the safety equipment one must wear, such as a respirator, gloves, chemical-resistant clothing, etc., when using the product.

An applicator must know the restricted entry interval (REI) listed for the product. The REI is a set amount of time after the application ends before a person can return to the treated area without wearing PPE.

Another term found on the label is the pre-harvest interval, which indicates the amount of time after the application ends until the crop can be harvested.

When a pesticide is applied to a specific site, it can move within that area or be moved off target and even off site. One common method of pesticide movement is drift. Drift is the movement of pesticides from the targeted site during or after application in the form of liquid droplets, dust particles and/or vapors. Drift can harm nearby people or animals and should be minimized as much as possible.

Drift can also cause adverse effects on non-target plants by causing damage called phytotoxicity. In some situations, this can be in the form of leaf burn, fruit peel burn or plant death. Drift can be minimized by making pesticide droplets larger by using adjuvants or changing spray nozzles, decreasing spray pressure and tractor speed, and not applying pesticides during windy conditions.

Pesticide characteristics significantly affect how and when a pesticide can move off site. These characteristics are adsorption, solubility, volatility and persistence.

Adsorption is the ability of pesticide molecules to bind with soil particles. Pesticide molecules bind more readily with finer-textured soils containing clay or organic matter versus larger, coarse soil particles low in clay or organic matter. The higher the adsorption rate, the less the pesticide moves off site.

Solubility refers to how well a pesticide dissolves in a solvent, typically water. The more soluble a pesticide is, the more potential off-site movement through ground or surface waters. Ground and surface waters can become contaminated in two ways: point source contamination and non-point source contamination.

Point source contamination happens if a known pesticide spill contaminated a nearby stream. The source of this contamination can be traced back to the spill. However, in non-point source contamination, the origin is unknown and can come from many sources. For example, pesticide levels found after testing the groundwater indicate contamination but cannot identify a single source of the contamination.

Volatility is the ability of a pesticide to change into a gas or vapor after application. This can be an issue in an enclosed space such as a greenhouse. Volatility can also be a safety issue for the applicator, nearby people and animals.

Persistence is the ability of a pesticide to stay active for an extended period after application. Persistence can increase the residual effects of a pesticide, which may be desired. However, contamination can lead to adverse environmental impacts if a pesticide remains in the environment longer than anticipated. Two examples of this type of persistent residual activity are bioaccumulation and biomagnification.

Bioaccumulation occurs when pesticide residues accumulate in the fatty tissues of animals and are not readily excreted. Over time, these levels increase in the animal. Biomagnification results in high levels of pesticide residue in animals due to the pesticide residue levels in the food they consume, typically other animals. An animal’s place in the food chain can potentially increase its likelihood of containing higher residue levels.

This article discussed some of the key terms every pesticide applicator should know. Many other aspects of pesticide use and safety are essential when using these products. Talk with your local University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Extension agent for more information on using pesticides correctly. Remember that the label is the law and must be followed accordingly. 

Source: Applying Pesticides Correctly, 7th Edition by F.M. Fishel, UF/IFAS

Ajia Paolillo is a UF/IFAS multi-county citrus agent based in Arcadia.

To request a hard copy of the article and test, or if you have questions regarding this article, test or CEUs, contact Lourdes Perez Cordero at or call (863) 402-6540 or (863) 402-7147. Please allow two weeks to process your CEU request.

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