Fertilizer vs. Pesticides: What's the Difference?

by Matt Gibson

Whether you’re trying to tend to a healthy lawn, grow a few flowers or vegetables, or manage an entire farm, whether or not to use pesticides and fertilizers is an issue that you will need to confront at some point. Though there are many negative effects that are reportedly tied to the use of pesticides and fertilizers, both are available in all-natural forms, and both are important factors in human health and safety. Learning how to use fertilizers and pesticides safely can help to limit risks and maximize the benefits of these important tools.

What Are Fertilizers?

Fertilizers are chemical or natural substances that are added to the land to increase its fertility. By fertilizing the soil, we supply our plants with the nutrients that they need to survive and thrive. By mixing fertilizers into your soil, your plants are more likely to grow more vigorously. Fertilizers function in two important ways. They supply the three big macronutrients (nitrogen, phosphorus, and potassium), three other macronutrients (calcium, magnesium, and sulfur), micronutrients (such as copper, iron, and zinc), and other agents (often fillers, which function in different ways) to the soil to add to and balance out the nutrients already present in the soil, that are often depleted after previous growing seasons of use. Some fertilizers also work to increase the effectiveness of the soil by improving its water retention capabilities and increasing aeration.

Advantages of Fertilizer

Fertilizer comes in many forms both all-natural and synthetic. Some fertilizers are chemically based, while others are derived from all-natural ingredients, such as dead leaves and old grass clippings. By offering vital nutrients like nitrogen to the soil, fertilizers help plants thrive despite the threat of disease or sharing their resources with invasive weeds. Organic fertilizers like compost and manure improve the quality of the soil by feeding the microorganisms that dwell within it. Feeding the soil’s microorganisms helps to reduce erosion and keep the soil aerated and hydrated. Cut grass clippings, scattered on the lawn, is another form of fertilizer that provides valuable phosphorus, potassium, and nitrogen and all you have to do to get it is mow your lawn.

Disadvantages of Fertilizer

Though fertilizers have plenty of benefits, they also have their drawbacks, as you might expect, especially with regard to synthetic fertilizers. Phosphorus, which is present in most fertilizers, can cause algae to build up in lakes and ponds, which eventually begins to kill the fish that live within the water by robbing them of oxygen. The overabundance of phosphates and nitrates within fertilizer can cause the contamination of our water sources as well. Runoff can lead to fertilizers contaminating the water source, which can make water unfit for human consumption. Synthetic fertilizers can also lead to more smog pollution, which can be linked to many respiratory illnesses, including asthma. This is due to a byproduct of many synthetic fertilizers called oxidized nitrogen.

What Are Pesticides?

Pesticides are any substance that is meant to control pests or weeds, including insecticides, herbicides, fungicides, animal repellents, and more. Pesticides are generally chemicals or biological agents, such as viruses, bacteria, or fungus, that discourages, incapacitates, or kills pests, such as insects, nematodes, microbes, or small animals that are known to destroy crops, cause nuisance, or spread diseases. Pesticides are classified by the target organism. For example, the most popular type of pesticide, by far, accounting for just over 80% of all pesticide usage worldwide, is herbicides, which target plants. Weed killers are a very popular herbicide, used in lawns, gardens, and farms regularly. Other popular types of pesticides include insecticide, which targets insects, fungicide, which targets all kinds of fungi, including blights, mildews, molds, and rusts, and repellants, which repel pests, including insects like the mosquito.

Advantages of Pesticides

The most beneficial advantage of using pesticides is their effectiveness against pests that could easily destroy crops in their entirety, devastating whole fields at a time. By controlling insect and rodent populations, pesticides help prevent the spreading of diseases. Insecticides protect buildings from termite infestations. By eliminating predators that would destroy crops and raise the cost of corn and cotton, pesticides keep the price of clothing and food down. Pesticides are even put to use in operating rooms to clean and disinfect surgical instruments and other equipment to keep the rooms and materials sterile and free of bacteria and microbial life forms.

Disadvantages of Pesticides

Despite the many positives of pesticide, they too have their disadvantages. Pesticides have reportedly been linked with deleterious effects on human health and a negative impact on the environment. In nature, pesticides wreak havoc on our ecosystem, polluting the water, air, and the ground itself. Exposure to pesticides could cause exposed plant and animal life to become sick and malformed. Children exposed to pesticides have increased rates of brain cancer and leukemia. Pregnant women exposed to pesticides have higher miscarriage rates.

Agricultural Benefits of Fertilizers and Pesticides

One of the main attractions to the use of fertilizers and pesticides are their numerous agricultural benefits. Plants feed off of nutrients that lie within the soil. These nutrients are needed for the healthy growth and development of plants. Over the course of time, if nutrient supplies are not regularly replenished, the soil will be incapable of sustaining plant life. Fertilizers are used to help reconstitute depleted soils and put these essential nutrients back into the ground. Organic fertilizers like livestock manure and compost do improve soil quality, but they release nutrients rather slowly, while manufactured fertilizers give the soil the quick nutritional boost that is sometimes needed during the growing season. Pesticides serve the agricultural world by helping to control pests that would otherwise damage or kill valuable plants, saving at least eight percent of worldwide crops each year.

Economic Advantages of Fertilizers and Pesticides

The use of synthetic fertilizers and pesticides in modern day agricultural practices have numerous economic advantages as well. Due to the use of fertilizers and pesticides, harvest yields are significantly increased each growing season, which in turn, lowers production costs and makes food more affordable. Plus, sufficient food can be grown to help support a consistently growing population, which keeps people healthy and productive. Synthetic fertilizers supply nutrients more efficiently and uniformly, are less expensive and can be transported more easily than organic soil amendment alternatives. Pesticide production is a multibillion-dollar business that significantly affects the US economic picture. Over 40 percent of agricultural goods that are manufactured in the United States are exported and sold elsewhere.

Environmental Impact of Fertilizers and Pesticides

Unfortunately, the many advantages of pesticide and fertilizer use are counterbalanced by problems that are directly related to their toxicity. One example is that beneficial insects that help balance the ecosystem are often harmed or killed by pesticides that are used to protect crops from harmful pests. The chemicals that are used in pesticides and fertilizers become runoff, which can drain into our streams and lakes, eventually contaminating our water supplies. Excess nitrogen from fertilizer runoff can cause algae growth in rivers and lakes. Too much algae can lead to the death of fish and other aquatic life, as excessive algae can deplete oxygen levels in our lakes, rivers, and streams, making it impossible for fish to survive.

Pesticides can even adversely affect the health of the farmers that use them on their crops because of working so closely with highly toxic chemicals. Pesticides can also affect those who live in large agricultural areas, as well as those who consume synthetic pesticide-treated foods. The World Health Organization estimates 1 to 5 million people worldwide are affected by pesticide poisoning each year and as many as 20,000 people suffer from pesticide poisoning annually.

The Problem of Resistance

Another problem that is associated with the use of pesticides is genetic resistance. The amount of insect pests and weeds that have become resistant to the use of pesticides has increased fivefold since the 1950’s. This means that more crops are destroyed by pests today, despite our many agricultural advances, than were harmed by pests in the 1940’s.

For the past 10,000 years, people have developed ways to domesticate plants and created cultivation techniques that have evolved our understanding of agriculture today. Early farmers provided their crops with food and fiber and changed very little in their cultivation practices for millennia. During the Industrial Age, however, fundamental changes took place in the world of agriculture, specifically the introduction of manufactured pesticides and fertilizers, and these changes have brought about agricultural and economic benefits and growth, but with it, came a significant growth of environmental problems.

The Use of Fertilizer and Pesticide In the United States

Agriculture and crop production in the United States has been aided by the use of fertilizers and pesticides for many years. As demands for crops like soybeans and corn soared, so did the amount of land that was dedicated to their production. Pesticide and fertilizer use has steadily increased alongside it. Nutrients essential to optimal plant growth are supplied by fertilizers, and pesticides that kill the weeds, insects, and animals that harm these crops, also help to boost production.

Fertilizer Use In the United States

The three broad categories of fertilizers are nitrogen, phosphorus, and potassium (NPK)-based. Rates of their combined applications grew after 1960, but have started to level off because of better practices. In 1960, total application rate was 46 pounds per acre per year (lb/acre/yr). By 2004, this rate had reached 146 lb/acre/yr, and now sits between 130-140 lb/acre/yr.

Nitrogen has had the highest application rate of the three nutrients and the biggest jump in use—in 1960, nitrogen application averaged 17 lb/acre/yr, reaching a peak rate of 82.5 lb/acre/yr in 2007. The nutrient accounts for approximately 59 percent of total fertilizer weight. Use of phosphorus and potassium (potash) has been pretty stable since 1960, with both nutrients maintaining rates between 25 and 36 lb/acre/yr since then. They account for around 20 and 21 percent of total fertilizer treatments, respectively.

The four aforementioned crops combined receive approximately 60 percent of all NPK fertilizers. Around 40 percent of total commercially applied NPK is put on corn, whose production is largely concentrated in the Midwestern states. Most soybeans are produced in this region as well, but the crop accounts for less than 10 percent of total NPK use.

This is mainly because soybeans are legumes and can fix their own nitrogen to use throughout the growing season. Corn needs more fertilization because it can’t sequester it’s own nitrogen, and harvesting the crop usually requires taking most of the plant, which results in more nutrients being removed from the field at the end of the season that must be replenished.

Pesticides In The United States

The use of pesticides grew rapidly in the United States after 1960 and acreage expanded to meet the increase in food demand. Application of pesticides increased as farmers recognized the low price of pesticides in comparison to other pest control methods such as tillage. Due to crop prices, weather issues, pesticide regulations, and inventions of new pest-resistant GE seed varieties, usage has been anything but uniform. Today, nearly $15 billion is spent on pesticides each year. This represents a five-fold increase since 1960 when adjusting for inflation.

Sixty years ago, herbicides accounted for only 18 percent of pesticide applications by volume on US crops and insecticides accounted for nearly 60 percent. These figures have changed drastically in recent years. Herbicides now account for approximately 76 percent of total applications and insecticides only six percent.

Adoption of herbicides grew so drastically due to low prices and the wide availability of different chemicals. Insecticide use decreased as new formulas were so much more effective, needing less product to achieve the intended goals. Today, corn, soybeans, wheat, and cotton receive about 80 percent of total pesticide usage.

Fertilizers and pesticides are very much commonplace in US agriculture, and production would not be where it is today without these vital inputs. Usage of and farm expenditures on fertilizers and pesticides have increased greatly after the 1960s as production areas grew, but has somewhat leveled off since because of diminishing returns and better growing practices. Growing demand for corn and soybeans will likely maintain strong total input requirements, even if usage per acre drops due to rising prices and adoption of smarter practices. Crops will always need nutrients though, and there will continue to be pests which need to be controlled.

Common Questions and Answers About Fertilizer Versus Pesticides

Can you fertilize and use pesticide at the same time?

Yes, you can apply fertilizers and pesticides at the same time. It’s especially easy to apply fertilizer and pesticide together using a spreader. To make the process easier, first measure out into separate containers the amount of fertilizer and pesticide you will need for your yard, garden bed, or whatever the area is you plan to treat. The packaging will have instructions including dosage amounts. Then mix the two containers together. Load the mixture into your spreader, setting the rate as directed by your package instructions. If the fertilizer and pesticide require different rates, use the fertilizer rate. You don’t want to apply the fertilizer at a rate any higher than the packaging recommends because doing so can damage your soil and plants. Apply the mixture with the spreader in a criss crossing pattern until the fertilizer and pesticide has all been used.

Can you mix pesticides?

Some pesticides can be mixed with good results, but some mixtures can lower the effectiveness of the product against pests, cause damage to plants, or lead to other problems when the products aren’t compatible. Follow the recommendations listed below if you wish to mix pesticides.

If you have not mixed certain products before, use a jar test (as directed below) as well as applying the mixture to a small area of your garden, then waiting for two or three days to ensure there are no ill effects before you apply the mixture to your entire garden. To perform a jar test, add a teaspoon of each product you plan to mix to a small glass jar, then fill it with water. Make sure to follow the order ingredients will be added as listed in the next bullet point when setting up this test. Close the jar, and shake it well. Watch the mixture for about half an hour for warning signs of incompatibility, which include settling to the bottom, creating a layered appearance, forming a gel, changing the temperature of the mixture, and flaking or creating other precipitates.

The order in which herbicide products are added to the tank is important. Follow this ordering system when adding ingredients to the tank: wettable powders, dry flowables, flowables, emulsifiable concentrates, and solubles. When compatibility agents (also called adjuvants) are used, they should be added to the tank first.

Do not mix an emulsifiable-concentrate insecticide with a wettable powder product. Emulsifiable-concentrate insecticides should also not be mixed with a fungicide or herbicide.

If a mixture causes crystallization, flaking, or another physical result that prevents your spreader or sprayer from functioning optimally, do not use this mixture.

Check the labels of all products you plan to mix, as they normally list incompatibilities, and some may instruct you on special care required during mixing, such as additional ingredients required when the product is used in a mixture.

Test the pH level of your mixture as well as the separate products (if individual pH is not listed on the packaging). When products don’t go well together, they often result in a very alkaline or very acidic pH level that must be counteracted to avoid damage to plants. Also, avoid mixing very acidic products with very alkaline products.

Limit your mixtures to one ounce of solid material per gallon of liquid to avoid buildup of too much salt or other ingredients that can harm plants in excess.

Do not mix phenoxy herbicides and iron sulfate. The mixture can result in a precipitate that clogs spreaders and spray equipment.

When using insoluble products, such as flowables or wettable powders, use no more than one soluble or emulsifiable chemical in your mixture.

Use the mixture as soon as possible after combining the products, because allowing the mixture to sit can result in deterioration of the materials.

Agitate the tank the entire time you’re creating the mixture, allowing it to run for a bit after each ingredient is introduced.

Certain types of product must be pre-mixed before being added to the tank. Refer to package instructions where available, or if they are not present, follow these guidelines. For wettable powders, mix with small amounts of water in a separate container until the slurry has a gravy-like consistency. Then add it to the tank. Dry flowables and water-dispersible granules should be premixed in a separate container with one part product added to one part water. Once mixed separately, slowly pour into the tank. Liquid flowables should be premixed in a separate container with one part product to two parts water or liquid fertilizer.

Do chemical fertilizers kill earthworms?

Salt-based artificial fertilizers do kill earthworms. Synthetic chemical fungicides and pesticides also kill earthworms. However, most organic fertilizers have a positive effect on earthworm populations.

Does organic mean no pesticides?

Some pesticides are allowed for organic farming, but they are generally not manmade pesticides. You can find out which pesticides are allowed in organic farming on the National List of Allowed and Prohibited Substances.

How long after spraying for weeds can I fertilize?

After spraying for weeds, you should wait at least a week before applying fertilizer to your garden.

Is it better to fertilize after mowing?

Yes, it is better to fertilize after mowing instead of mowing after fertilizing. Fertilizing after mowing allows the fertilizer to take effect before mowing, which can redistribute the fertilizer. If you are going to fertilize after mowing, leave a small amount of grass clippings on your lawn, as these contain beneficial nitrogen.

Is it OK to mix fungicide and insecticide?

Most fungicides and insecticides can be mixed, but some should not be, so make sure to read product labels for incompatibilities before mixing fungicide and insecticide. Also, make sure to abide by the following guidelines.

Do not mix fungicides that contain sulfur with insecticides that contain deltamethrin.
Do not mix fungicides that contain copper or lime sulfur with insecticides that contain lufenuron.
Check the application schedule to ensure compatibility. Some products should be applied while plants are actively growing, while others should be applied while plants are dormant.
Do not combine wettable powders with emulsifiable concentrates.

Should grass be cut before fertilizing?

If you need to both mow the grass and apply fertilizer, it is better to mow first and then fertilize than to fertilize before mowing. If you will be applying fertilizer after mowing, leave some grass clippings on your lawn to take advantage of the beneficial nitrogen they contain.

Should I fertilize or kill weeds first?

Apply weed killer before fertilizer, because weed killer stresses plants somewhat, and the fertilizer will help them recover. You can apply fertilizer within days of using a weed killer, or you can even apply the two products on the same day. Just wait at least 30 minutes after treating with weed killer before applying fertilizer. If the weeds have been particularly difficult to kill, you may wish to wait until they are dead from the weed killer before applying fertilizer.

What is pesticide toxicity?

Pesticide toxicity refers to a product’s capacity for causing injury or illness. Pesticide toxicity is determined by testing the active ingredients in pesticides on animals at various dosages. There are two levels of pesticide toxicity: acute and chronic. Acute toxicity describes a product’s capacity to cause injury or illness after one instance of coming into contact with the product. Chronic toxicity describes the effects of long-term contact with the product.

What is the best fertilizer for root growth?

Fertilizers that are high in phosphorus and potassium are the best for encouraging root growth. These fertilizers are most useful during a plant’s active growing period. Phosphorus and potassium will also encourage fruit or flower production in your plants. Fertilizers are labeled with a string of three numbers separated by hyphens, such as 3-20-20. The numbers note the percentage of nitrogen, phosphorus, and potassium a fertilizer contains, in that order. To find fertilizers high in phosphorus and potassium, look for fertilizers with high second and third numbers.