Insecticides, herbicides and fungicides, collectively known as pesticides, are chemicals that are used in agricultural pest control. Learn about their impacts on the environment and public health.
Our industrial agricultural system relies heavily on pesticides, which control weeds, kill insects and stave off fungi. More than 1.1 billion pounds of pesticides are applied annually to crops in the US1, mostly in combination with seeds that are genetically engineered to withstand them. The escalating use of pesticides in recent decades has become a public health hazard, an environmental disaster and has even caused the evolution of “superweeds,” which require increasingly toxic pesticide formulas to kill. Consumers can help reduce the demand for products grown with pesticides by purchasing organic or low-spray produce and by joining organizations fighting against the powerful multi-billion-dollar pesticide industry.
Industrial agriculture relies on two types of chemicals: fertilizers and pesticides. The former boost soil fertility, making crops more productive, while the latter protect crops by controlling weeds (herbicides), insect and animal infestation (insecticides and rodenticides) and fungal/mold diseases (fungicides).2
Pesticides come in a variety of formulations, depending on their target and purpose. For example, fumigants are applied as gases to the soil, and “systemic” pesticides are absorbed by leaves before spreading through the rest of the plant. Not all pesticides and formulations are created equal — some chemicals can harm a wide variety of non-target species, and some application methods have high potential to drift off target. This means that pesticides can cause harm to the wider ecosystem, instead of just their intended targets. This presents a real risk for biodiversity and environmental health.
Pesticides are not a modern invention. Ancient Sumerians used elemental sulfur to protect crops from insects, and medieval farmers and scientists experimented with chemicals like arsenic. Nineteenth-century research focused on compounds made from plants, including chrysanthemum. In 1939, dichlorodiphenyltrichloroethane, better known as DDT, was discovered to be extremely effective against both agricultural and disease-carrying insects. It rapidly became the most widely used insecticide in the world. Twenty plus years later, shortly after Rachel Carson’s Silent Spring shed light on the devastating effects of DDT on the environment, serious concerns about its impact on human and animal health led the US and 80 more countries to ban its use. The book also galvanized the environmental movement and the creation of the EPA, which is still responsible for monitoring pesticide use.3
As agriculture has grown and industrialized, farmers have come to rely on pesticides for large-scale practices such as monocropping — growing one crop in great quantities, season after season, on the same land. Despite the widespread recognition that pesticides are harmful to human and environmental health, our industrial agricultural system depends on their continued use.
For farmers, pesticides save labor and generally provide a higher yield: they can mean the difference between saving a crop and losing it to disease. Some farmers, especially those who grow produce at a smaller scale, use pesticides sparingly. For example, fruit trees are susceptible to disease in northeastern regions, especially at the blossom stage. An apple or peach grower may spray their fruit trees with a fungicide once in the spring to ensure that the fruit sets, but use no further chemicals for the rest of the season.
For many large row crop farmers, on the other hand, regular pesticide use is as much a part of farming as planting seeds. Spraying Roundup on a field of corn genetically engineered to withstand the chemical kills the weeds without affecting the corn. In comparison to mechanically weeding hundreds or thousands of acres, using pesticides is a game-changer. Some farmers spray their wheat with a weed-killer at the end of the season to speed its drying process and prevent losses from wet weather later in the season. Farmers growing fruit or vegetables on a large scale, especially delicate varieties like strawberries, will blanket the field with pesticides to ward off any possible disease.
More than 90% of corn, soybeans and cotton in the US are genetically modified to be resistant to herbicides.
The carpet-bombing approach to pesticide use is a hard habit to break. Decades of using pesticides as the first and only line of defense mean that older, traditional knowledge and skills about pest and weed management have been lost, which leaves farmers out of options if and when the chemicals fail. Buying equipment and investing time and labor costs into alternative pest control methods can be restrictive for many farmers, especially those who have heavily invested in engineered seeds and pesticides.
The most recent report on pesticide sales and use from the US Environmental Protection Agency (EPA) puts US pesticide use at 1.1 billion pounds in both 2011 and 2012, which amounts to 23 percent of the nearly six billion pounds used worldwide. 4 Agriculture accounts for nearly 90 percent of pesticides in the US, with industry/commercial/government and home and garden use making up the rest.
Herbicides are the most common type of pesticide used, accounting for almost 90 percent of the pesticides used by the agriculture sector.5 Monsanto, an agrochemical company now owned by Bayer, is well known for its line of “Roundup Ready” seeds, which are resistant to glyphosate, the main ingredient in the herbicide “Roundup”. The combination of the two products allows farmers to spray entire fields with glyphosate without fear of losing their main crop. This makes pest control on crops like corn and soy easy for farmers, and the technology has been very popular — herbicide-resistant seeds account for more than 90% of corn, cotton, and soybeans planted today, 6, and the volume of glyphosate used in the US increased tenfold from 15 million pounds in 1996 to 159 million pounds in 2012. 7
The agricultural chemical companies and their trade associations (with names like CropLife), motivated by profit, are highly invested in keeping farmers reliant on pesticides. Pesticides are a $14 billion industry in the US; two-thirds are for agricultural use. Most of those sales are herbicides paired with genetically modified seeds, but these numbers do not include sales of the seed itself. In 2017, Monsanto’s net sales of genetically engineered (GE) corn, soybean and cotton seeds and associated GE technologies totaled $9.5 billion. 8
As the industry has exploded, the companies involved have grown and merged. What started out as six major agricultural chemical companies had, by 2018, merged into just three: DowDuPont, ChemChina and Syngenta and Bayer/Monsanto. 9 This much control concentrated in a few mega-corporations means fewer options for farmers, as well as higher prices — and increasing political power for the companies.
The agrochemical industry has been politically powerful for many years. 10 As a bloc, the agricultural inputs sector spent nearly $33 million in lobbying Congress in 2016. 11 The “revolving door,” by which former industry leaders serve in the government agencies overseeing their industries, is well-used by agribusiness, mainly to keep regulation of pesticides and other agricultural products and practices extremely limited. 121314
The ag chemical industry also influences the scientific research that guides policy-making: as public spending on agricultural research and development has been cut precipitously, industry now funds a much larger share. 1516 This means that they may decide not to investigate certain issues or may withhold results that are unfavorable to their products. 17 The best-known example is the debate around the herbicide atrazine; independent research frequently shows it is harmful to wildlife, while industry-funded research consistently finds no negative consequences. 18 In this case, this has led the EPA to reverse guidelines on atrazine use several times, with tolerances currently well above what researchers believe are harmful.
The outcry following the publication of the 1962 book Silent Spring — which documented the detrimental environmental effects of overuse of pesticides — resulted in DDT being banned in the US and created an awareness of how pesticides can impact the wider environment. Pesticides that are sprayed on crops leave a residue on the dead plant material that settles into the soil and can run off into waterways or leach into groundwater. A 2014 study performing tests across 38 states found glyphosate in the majority of rivers, streams, ditches and wastewater treatment plants, as well as in 70 percent of rainfall samples. 19 Even at levels deemed safe, pesticides have been shown to cause a loss of biodiversity, including reduced numbers of beneficial insects, as well as birds and amphibians. 20 The EPA maintains a list of the potential effects of pesticides on aquatic life and other animals as a reference for researchers investigating water quality. 21 Some pesticides, such as atrazine, may not usually be present in quantities to kill wildlife outright, but they can still disrupt breeding and cause serious damage to aquatic foodwebs.
In addition to endangering wild ecosystems, insecticides also cause problems on the farm — many of these species are important pollinators for fruit, nut, and vegetable crops. Neonicotinoids (or neonics), a popular class of pesticides that attack the nervous system of insects, have grown in popularity since the 1990s due to their comparatively low toxicity to mammals and humans. However, a widening body of research links neonics to decline of wild and domesticated pollinators; bumblebee colonies exposed to neonics in controlled trials grew more slowly and produced fewer queens than those without exposure 22 and experiments in honey bees have found neonics reduce impair learning and communication. 23 Even more concerningly, honey bees seem to prefer food sources that contain neonic residues.24 Neonics aren’t the sole reason honey bee colonies are collapsing, but when combined with the other stressors colonies face in our industrialized food system, like varroa mites, being moved hundreds of miles to pollinate different crops, and huge, monocultured biodiversity deserts, they pose a serious threat. While the EPA banned 12 neonic formulations in 2019, many more remain on the market. 25
Another on-farm problem stemming from over-reliance on pesticides is the evolution of pesticide resistance in insects, weeds, and diseases. Like all living things, weed and pest populations evolve over time. When farmers repeatedly apply the same pesticides, they eliminate most of the population that’s susceptible to the chemical. However, natural genetic variation means that occasional individual pests might be resistant to the pesticide and survive. When the same pesticides are applied year after year on a massive scale, these resistant individuals quickly multiply until the whole population is resistant to the pesticide.
Weeds that have evolved resistance to multiple herbicides, termed “superweeds,” pose a serious threat to farmers who find their fields overrun with weeds they lack the tools and the knowledge to kill. Herbicide resistance is increasingly common, and some areas may have multiple herbicide-resistant weed species in their fields, making weed control even more difficult.26 In just the US, scientists have already discovered 25 species of weeds that have grown resistant to herbicides. 27
With annual US losses estimated at $10 billion, pesticide resistance is an expensive problem for American farmers. 28Rather than addressing the root causes of resistance, however, agrichemical companies simply release new formulations of multiple herbicides. Sometimes, these new formulations contain older, more hazardous chemicals like dicamba, atrazine, and 2,4-D. These reformulations can lead to massive increases in the amount of chemicals sprayed on crops — the newly approved combination of glyphosate and 2,4-D, for example is expected to lead to a 300 to 700 percent increase in the chemical’s use by 2020. 29
In addition to keeping farmers on a kind of treadmill of buying new formulations of pesticides, pesticide resistance can have serious off-farm consequences. For example, overuse of insecticides can cause non-target species to develop resistance as well—just as antibiotic abuse on industrial farms puts the public at risk by encouraging antibiotic-resistant infections, there’s evidence that agricultural insecticides have contributed to the spread of insecticide-resistant mosquitoes. This poses a huge difficulty for public health professionals trying to prevent malaria and other diseases.30
Depending on how they’re applied, some pesticides can drift off target and damage other crops. For example, dicamba, which was previously approved only for ground spreading, was EPA-approved in 2017 for aerial spraying in conjunction with soybean seeds genetically engineered to be resistant to the chemical. While farmers were optimistic that dicamba would be a useful tool against glyphosate-resistant superweeds, the situation quickly soured; dicamba is extremely volatile: even when applied according to label instructions, it can turn back into gas and drift several miles, killing or damaging any plant material wherever it lands. In this case, dicamba drift damaged 3.6 million acres of non-resistant soybeans in neighboring fields, as well as vegetables, fruits, and trees in 25 states. 31
If a farmer chooses not to grow pesticide-resistant crops and a neighboring farm’s pesticide drifts over, it can damage or ruin that farmer’s crop, causing bitter conflict among farming communities. Rather than rejecting this damaging chemical altogether and sanctioning the seed and chemical manufacturer for bad practices, the soybean growers decided instead to plant dicamba-resistant seeds; this has further expanded the use of the herbicide, benefiting the bottom line of the seed and chemical manufacturer, and also increasing the possibilities of dicamba drift. Even organic agriculture is impacted by pesticide drift: in addition to causing crop losses, pesticide drift can cause organic crops to test positive for pesticide residues and ruin a neighboring farm’s organic certification, which limits farmers’ ability to be fairly compensated for the higher costs of cleaner production.
Pesticides also pose serious risks to human health and safety. Because of their widespread use, people in every part of our food system — producers, workers and consumers — can be exposed to potentially harmful levels of pesticides.
As part of the approval process for new pesticides, the EPA assesses possible health impacts, drafts usage guidelines and establishes tolerances, or amounts allowed on or in a food. 32 The US Food and Drug Administration (FDA) and USDA annually survey and publish information regarding pesticide residues in the food supply.33 34 However, many EPA-designated tolerance levels may not fully account for a range of health risks, such as hormone (or, endocrine) disruption. 35
The people most at risk from pesticides are the farmworkers who apply them and who work in the fields where they are used. While the federal government regulates how pesticides are used and sets guidelines to limit exposures, these guidelines aren’t always followed. For example, farmworkers may not be given required protective equipment, or could be forced to work on recently-sprayed fields with unabsorbed pesticides. Since many of the farmworkers in the US are undocumented immigrants with limited English skills, they may not be given appropriate training or be able to understand warning signage, and they may even be pressured into working in unsafe conditions. These barriers also mean that incidents of pesticide poisoning in farmworkers often go untreated—workers experiencing poisoning from chlorpyrifos, for example, might just think they have a bad case of the flu.36
Farmworkers who are victims of pesticide poisoning may also lack the financial and legal resources to report incidents, so they often go uncompensated. The fact that these incidents are often underreported also means the real impact of pesticides is underestimated in public health research that influences policy and legislation.37
In addition to acute poisoning from field exposures, pesticides can also cause longer-term health impacts for workers and consumers, and even people who live around farms where they are used. Chlorpyrifos and other organophosphates, for example, are harmful to brain function and are associated with preterm births and neurological disorders among people working on farms and living in agricultural areas. Studies have concluded that the pesticide is especially dangerous to children, even in utero. 3839 Given the magnitude of evidence showing the impact to human health, and the decision of the EPA to delay banning the pesticide, three US states — New York, California and Hawai’i — have moved to ban the use of chlorpyrifos. 40
Other pesticides, like endocrine disruptors, have been linked to low birthweight, abnormal brain development, increased incidence of cancers and reduced fertility among people who live in agricultural areas.41 Even legally approved pesticides can be carcinogens; a 2010 report by the President’s Cancer Panel concluded that pesticides were associated with numerous types of cancers, including brain, pancreatic, non-Hodgkin lymphoma, myeloma, colon, testicular and soft tissue sarcoma.42
There is ongoing debate about possible cancer risks of glyphosate. In 2015, the World Health Organization analyzed the existing research on glyphosate and classed it “probably carcinogenic,” having found some evidence of an increased prevalence for non-Hodgkin lymphoma after glyphosate exposure. 43 However, a similar EPA declared glyphosate as unlikely to be a carcinogen. 44 The EPA analysis incorporated research from additional sources, including unpublished data that was provided directly from Monsanto itself. This was excluded by WHO’s standard of only using publicly available data, and cast doubts on the EPA findings’ legitimacy. 45
Determining if substances are carcinogenic is complicated, and part of this difficulty comes from the types of studies used in the process. While experiments using cells or animals in a lab setting may show that glyphosate can cause cancer, other studies focus on whether or not cancer is a likely, real-life outcome. In this case, a supplement to the WHO declaration concluded that glyphosate is “unlikely to pose a carcinogenic risk to humans from exposure through the diet” but recommended further study given their finding that it could cause cancer in mice at high doses. 46 It’s important to note that observational and associational research, which observe correlations between factors without performing experiments, are categorized as “weaker evidence” in these types of assessments and don’t get much weight. However, they can still point to concerning connections that aren’t always picked up in lab studies. In Sri Lanka, for example, researchers found a high correlation between glyphosate use, water contamination, and kidney damage. 47 So while it looks unlikely that glyphosate residues in food directly cause cancer in consumers, there’s plenty of cause for further investigation of health impacts. In spite of the unsettled science, several recent court cases have found Monsanto liable for life-threatening illnesses among people who had extended exposure to the chemical, and there are thousands of similar lawsuits in progress. However, the EPA filed a brief in support of Monsanto in one of the largest cases, restating their own findings of no harm – given the size of the companies involved and the huge role glyphosate plays on American farms, it’s unlikely the legal battles will end soon. 48
While USDA testing consistently finds that nearly all food samples have pesticide residues, the levels are typically well below the tolerance levels established by the EPA. However, these tolerances are set for individual pesticides; in reality, residues from multiple pesticides are often found together in the same foods, and the way that these residues interact is unclear. 49 Recent analysis by the Environmental Working Group (EWG) showed that 70 percent of produce samples were contaminated with pesticide residues. The type and amount of residue found on food can depend on many factors, like how the pesticides were applied, and whether or not the foods had a thick peel. 50
Since consumers can’t always see how their food is produced, the EWG’s annual Dirty Dozen and Clean Fifteen lists provide details about what foods have the most and least pesticide residues. Eating lots of fresh produce is an important part of a healthy diet, but that doesn’t have to mean ingesting lots of pesticide residues. Tools like the Dirty Dozen can help consumers know what foods they should prioritize buying organically-grown to minimize their exposure to pesticides.
Reducing or eliminating pesticide use requires careful ecosystem management, using crop rotations and good soil health practices to build a population of beneficial microorganisms, insects and plants that will do the work of warding off diseases and weeds. Small changes can have a big impact; a 2012 Iowa study, for example, found that simply adding an additional crop such as oats into the common rotation of corn and soybeans allowed farmers to use far less herbicide for weed control and to dramatically cut water contamination, while maintaining similar yields. 51
Integrated Pest Management (IPM) embraces a continuum of practices among farms of all sizes, beginning with identifying pests before spraying. For instance, an IPM farm may grow pest-resistant crop varieties, use predatory insects to kill plant-eating pests, employ mechanical pest traps and eliminate pest nesting areas. 52 If further control is needed, IPM farmers would employ a targeted approach, using broadcast spraying only as a last resort.
Other techniques used by sustainable farms to reduce the need for pesticides include planting cover crops, strategically timing weeding and tilling, and starting crops early or late to outcompete weeds. All of these decisions take careful observation of the on-farm ecosystem, and many of them require more labor than just spraying a pesticide. This is part of the reason sustainably produced food is sometimes more expensive on the supermarket shelf.
Farming that does not rely on chemical pesticides requires more specialized knowledge, time and labor on the part of the farmer; thus, the products are often more expensive. As a consumer, if you can afford the extra cost, you are making an investment in a healthier agricultural system for everyone. Purchase organic and sustainably produced foods at your local farmers’ markets or farms, where you can ask the farmer directly about his or her pest control methods.
Previous page photo by Dusan Kostic/Adobe Stock.