What Are Pesticides and Why Do We Use Them?

Often times when people talk about using chemicals on the farm, they use the word "pesticides." To people outside of agriculture, pesticides tend to be the lump all category for any and all chemical compound we spray on our crops. And honestly, that is far from the truth. We don't have a jug labeled "pesticides" that goes on anything and everything. In agriculture, we call any sort of chemical we use on the farm crop protection products. 

The truth about the crop protection products we use on the farm is that we use specific chemicals labeled for very specific uses and at very specific amounts. I've written before that as farmers we have a choice in what seed to select. We also have a choice when it comes to what we put on our crops. It varies depending on crop, soil, crop rotation, current condition of the crop, pests, and moisture. The choices we make for what to spray is careful, calculated, and measured out. It is not something we do haphazardly or thoughtlessly like many other websites will suggest. 

In the agriculture world, we typically categorize crop protection products under many different types. I want to share with you those different types, why we use them, and how they affect the crops on our farm. In order to understand how and why we use certain chemicals, it is important to understand the science behind how and why they work. Think of it like this, if you were looking to clean your floor, you wouldn't use the soap formulated to clean your dishes. You would use whatever is specific to that particular task. 

I have done my best to break this down in the simplest terms I can. I understand this is a hot topic and I ask that if you choose to comment, please be respectful. 


Much like your home or garden, controlling weeds is important to ensure your crop grows. Since the 1940's, a new breed of herbicide was born that allowed for relatively low rate of chemical applied, using low volumes of water, and are selective meaning that we can kill the weed without harming the crop plant. 

Herbicides work in several different ways by affecting their target weeds: destroying cell and tissue, preventing cells from dividing so the plant cannot grow, promoting uncontrolled growth that kills the plant, or by disrupting vital enzyme systems within the plant. 

We call these different methods modes of action and it is through these modes of action herbicides are categorized. For example, glyphosate (Roundup) is a mode of action that inhibits an enzyme, which is vital for plants to make particular amino acids. Without these amino acids, the plant dies. Animals do not require this which means glyphosate has relatively low toxicity to mammals, insects, and fish. 

Herbicides are also categorized by what we call a mode of uptake. Not all herbicides reach the plant in the same method. Some herbicides act on the plant when they first touch it, some herbicides are absorbed from the soil by the roots, and some herbicides enter the plant by absorption through the leaves. 


Insecticides are chemicals used to control insects by killing them or preventing them from engaging in behaviors that are destructive to crops, like eating them. Many insecticides act upon the nervous system of the insect by inhibiting or blocking enzymes.

Much like herbicides there are varying modes of entry to insecticides to work. Residual insecticides remain active in amounts sufficient to kill pests for a specific amount of time. These residual insecticides act by keeping a toxic residue on a surface that the insect will come in contact with.

Contact insecticides control the pest on contact and are applied directly to the insect, which is killed after it comes in contact with the insecticide. Very little toxic residue remains on a surface after spraying a contact insecticide. Think about when you fog for mosquitos or flies.

Systemic insecticides enter the insect's host plant and translocate throughout the host plant. When an insect feeds on the host, it ingests enough insecticide to be lethal. And finally stomach poisons are insecticides eaten by an insect so that the poison enters the stomach and is then absorbed into the body.

Insecticides are also classified by their chemical basis. These are big, scientific words but here are several of the classifications: organophosphates, carbamates, miticides, pyrethoids, and neonicotinoids. If you are interested in reading more about these classifications, here is a great write-up.


Disease is a major source of crop and plant damage that can be caused my fungus. Fungicides are used to control fungal disease by specifically inhibiting or killing the fungus causing the disease. In contract with human medicines, most fungicides need to be applied before the disease occurs or at the first appearance of symptoms to be effective. And also unlike humans, the damage caused by diseases on plants often does not go away, even after the pathogen is killed. Fungicide can only protect new uninfected growth from disease, so you can see why fungicides play an important role in crop protection.

Like insecticides and herbicides, there are different classifications of fungicides. Contact fungicides remain on the surface of plants while Systemic fungicides are absorbed into the plant. There are also different modes of action. Fungicides kill fungi by damaging their cell membranes, inactivating critical enzymes, or by interfering with key processes such as energy production or respiration.

Pesticide Summary

Knowledge of exactly how an herbicide, insecticide, and fungicide is affects its' target is helpful and critical for selecting products. Products are not just selected at random, but as I said before, are carefully chosen with many factors taken into consideration. Often times, farmers will consult a professional called an agronomist to make pesticide recommendations. Knowing the mode of action determines how the pesticide will affect the target. Sometimes different modes of action are needed in successful and effective crop protection. One of the reasons we rotate our crops is so that our soil isn't getting the same modes of action year after year.

Please remember that we are all people, no matter what side of the fence we are on. Whether we are organic farmers or a conventional farmer or anyone in between, we are all people. We have families, friends, and people we are about. We are all passionate about the food we eat and how it ends up on our tables. We all care about the health and safety of those we love…farmers are no exception.

Look at this list, look at the choices we are offered as farmers. Let's celebrate that choice. Let's celebrate that farmers are given choices so we can produce the very best crops we possibly can so that you, the consumer, can have choices when it comes to the food you find in the grocery store and beyond. And finally, let's all work together, have conversations, and further research so that more people across the globe can be given those choices too!

Jenny Rohrich


Jenny Dewey Rohrich is a self-proclaimed country girl. Born and raised in Northern California and growing up in her parent's butcher shop and deli (chicolockersausage.com), agriculture has always been close to her heart. She recently followed her heart all the way to the rural prairies of North Dakota where she is now married to a Sunflower farmer and works at his Ag supply business. Jenny and her farmer still cannot believe they found found love via Twitter and their life became a true modern day love story. Besides spending time with her farmer, Jenny can be found with a camera in hand capturing the world around her, loves the challenges of bringing culture to the North Dakota prairie through a variety of culinary creations, and using her interior design degree to flip their bachelor pad into a home in their small town of Ashley (population 800). All of this and more can be found on her blog: prairiecalifornian.com. You can also find her on Facebook!

related topics: farming, agriculture, pesticides

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