How Do Pesticides Work?

The U.S. uses around 1 billion pounds of conventional pesticides each year to control weeds, insects and other crop-damaging invaders. Pesticides are crucial for protecting crops but can also be mismanaged at great risk to the environment.

How Do Pesticides Work?

Explainer Science Technology

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The U.S. uses around 1 billion pounds of pesticides each year to control weeds, insects and other invaders from damaging crops and lawns. These chemicals play a crucial role in protecting crops but their overuse and mismanagement has also harmed farm workers and wreaked havoc on the environment.  

What Are Pesticides?

According to the Environmental Protection Agency (EPA), anything that is used to mitigate pests, control plants or manage nitrogen in the soil is considered a pesticide. All pesticides contain two different kinds of ingredients: active and inert. Active ingredients are those that are actually responsible for controlling pests. There are a variety of different substances, including simple chemicals, compounds and even food items that the active ingredients are combined with to make pesticides — these are called inert ingredients. Just because these substances are not considered active does not mean that they are not toxic. 

Brief History of Pesticides

The practice of applying pesticides dates back as far as agriculture itself, with the first recorded use a mixture of salt, sulfur and heavy metals. However, it wasn’t until the 19th century that the first purpose-made chemical pesticides started being produced. One pesticide, originally marketed as a coloring agent called “Paris Green,” was marketed as a pesticide for a century starting from the 1860s. 

In the mid-20th century DDT took the agricultural world by storm. However, it didn’t take long for the chemical’s side effects to be discovered, famously reported in Rachel Carson’s book Silent Spring. In part thanks to publicity from the book, DDT lost favor by the 1970s, with most countries discontinuing its use by the 1980s. Today, DDT is classified as a probable human carcinogen, and a persistent chemical that is still found in soils around the world decades later. 

However, as agricultural technology continues to advance, pesticide use has the potential to decrease in favor of genetically modified organisms (GMO). Already, 92 percent of the corn being grown in the United States is GMO. Much of it has been specifically modified to be more resistant to pests, reducing the need for additional pesticides. Most corn and soy grown in the U.S. is also bred to be resistant to the herbicide glyphosate — which means farmers can apply the pesticide without harming crops. 

How Do Pesticides Work?

As one might expect, different pesticides work in different ways due to their varying end goals. Some pesticides focus on eliminating certain bugs or animals, while others protect against undesirable weeds. 

Most insecticides work by inhibiting the transmission of messages between neurons in the insect. Eventually, the impacted bugs die from the neurons randomly firing, causing spasms. Herbicides, on the other hand, work by blocking different functions of the target plants such as cell division or photosynthesis.

Six Types of Pesticides

The most widely known types of pesticides are insecticides, fungicides, rodenticides and herbicides. Another way of differentiating between different pesticides is by their ingredients. When broken up this way, there are two classes of pesticides: conventional pesticides and biopesticides.


Insecticides are pesticides that are specifically engineered to target insects likely to harm crops. There are numerous different types of insecticides and they are classified by their type and mode of action. Among them are organochlorines that act on neurons, carbamates that cause twitching and eventually paralysis and pyrethroids that impact both the peripheral and central nervous system.


Herbicides target undesirable plants that could destroy or otherwise harm the crops being grown. In addition to the role they play in agriculture, they are sometimes also used for managing forests and in suburban and urban areas on golf courses, lawns and gardens. Herbicides can be separated into four categories based on how they work. They are amino acid inhibitors, photosynthesis inhibitors, growth regulators and cell division inhibitors. 


The goal of fungicides is to prevent the development and spread of fungi that could harm plants. However, fungicides are not effective against all types of fungal-caused diseases so it is recommended that growers identify the pathogen before applying such a pesticide. 


Many rodents are considered pests due to their tendency to consume food grown both commercially and residentially. Rodenticides do not only impact rats and mice but also squirrels, chipmunks and beavers. These pesticides can also be lethal to other mammals and even birds if consumed. Rodenticides are not just used to prevent the destruction of food but also to eliminate rodents from homes.

Conventional Pesticides

Conventional pesticides are used in vast quantities in the United States. These chemicals are widely applied to fields of crops even though some have been linked to detrimental effects on both public health and the environment. Each chemical poses different types of risks — some of which can be mitigated with careful use and application through an approach called Integrated Pest Management.  


A biopesticide is one with ingredients derived from natural sources such as animals, plants and minerals. Within the umbrella of biopesticides there are biochemical pesticides, microbial pesticides and plant-incorporated protectants that are derived from plants that have had genetic material added. Biopesticides represent a less toxic alternative to conventional pesticides. 

What Are Five Examples of Pesticides?

Following a series of mergers that took place from 2015 to 2018, the pesticide market is controlled by just a few companies. Bayer acquired Monsanto, ChemChina acquired Syngenta, and Dow Chemicals and Dupont merged and then split into three parts, with agribusiness going to the newly formed company Corteva. These companies are responsible for most of the pesticides that are used as part of plant production systems, both commercially and residentially. 

Some of the pesticides produced by Bayer-Monsanto include Roundup, a widely available herbicide, and Sivanto, an insecticide available for use on a variety of different crops. Meanwhile, Corteva Agriscience owns the herbicide Arlex Active, the fungicide Adavelt Active and the insecticide Isoclast Active, among other pesticides. 

Are Pesticides Harmful to Humans?

Pesticides have a long history of negatively impacting human health. Perhaps the most well-known example is DDT (Dichloro-diphenyl-trichloroethane). The chemical has not been used in the United States since it was banned by the EPA in 1972. However, the effects of the chemical still haunt people to this day. Research shows the daughters of women exposed to DDT are more likely to develop breast cancer, hypertension and obesity than other women.  

Another controversial pesticide — in this case an herbicide — is glyphosate. In 2015, the World Health Organization’s International Agency on Cancer Research classified glyphosate as a probable carcinogen. Subsequent reporting in Reuters revealed, however, that evidence suggesting no cancer link was excluded from deliberations. Adding another layer of complexity is IARC’s particular way of communicating risk. Dubbed “confusogenic” by Atlantic science writer Ed Yong, the agency evaluates the strength of existing evidence for cancer rather than the actual risk. The EPA’s most recent analysis finds glyphosate not likely to be a human health risk. 

Farmers and farm workers who work directly with pesticides experience a much higher level of chemical exposure than consumers eating conventional fruits and vegetables. Some farmers report a variety of adverse health impacts including the formation of lumps on their skin. Paying close attention to farmers and their experiences is necessary, especially given that every year there are an estimated 385 million cases of acute pesticide poisoning among farm workers worldwide. Potential side effects of acute exposure include headaches, nausea impairment of the senses and damage to the nervous system. 

What Are Pesticides’ Environmental Effects?

One recent study from an environmental advocacy organization projects that the use of pesticides will continue to rise as climate change worsens. The group called for an end to their widespread use due to the destruction they wreak on the environment, including their role in causing climate change. Some pesticides, such as sulfuryl fluoride, are greenhouse gases in their own right, while most are derived from fossil fuels. Overusing herbicides can also lead to soil erosion, as misuse and overuse can destroy soil-dwelling organisms that otherwise help to ensure that the land maintains its nutrients. 

What Rules Govern Pesticides?

There are a number of different laws that regulate which pesticides can be used and how. Perhaps most significant is the Federal Insecticide, Fungicide and Rodenticide Act which requires that all pesticides distributed in the United States are registered with the EPA. The Federal Food, Drug and Cosmetic Act requires that a maximum level of pesticide residue on food is set. The Food Quality Protection Act of 1996 created a more stringent rule that in order to be registered a pesticide must be reasonably believed to do no harm. In addition, fruits and vegetables produced under the organic standard in the U.S. can only be grown with certain permitted pesticides, virtually all of which are natural in origin, not synthetic. 

What Are the Alternatives to Pesticides?

Despite being the default for controlling unwanted animals, plants and other organisms, there are alternatives to pesticide use. Some farmers use a variety of approaches to minimize their pesticide use, including integrated pest management and some of the practices described below.

Cultivation Practices

Some farmers have found success shifting the way that they farm. This protects not only the environment but also the farmers themselves from the impacts of pesticides. 

Use of Other Organisms

Instead of defaulting to pesticides, experts have suggested cultivating healthy populations of the natural predators of unwanted insects and plants. 

Biological Control Engineering

Pest species, whether plants, animals or fungi, have natural predators that can be introduced to avoid having to use pesticides. In fact, applying pesticides is likely to wipe out the natural enemies of common pests, opening the door for the unwanted organisms to reinfest the area.

Laser Weeding

An emerging method of controlling weeds is through the use of lasers. Laser weeding is more environmentally friendly than using herbicides. Plus, instead of running directly on fossil fuels like most mechanical weeding, employing lasers uses electricity, potentially reducing its environmental impact. 

What You Can Do

The role of pesticides in our food system comes with trade-offs — powerful chemicals protect against crop loss but on the other hand, their widespread use (particularly of the more toxic pest-control methods) can harm workers and the environment. Supporting legal protections for farm workers is one way to help. While growing your own food is not a scalable food system solution, community and backyard gardens provide access to fresh fruits and vegetables — and we have heaps of evidence that shows consuming more fruits and vegetables is good for your health.

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