Farmers apply a wide range of chemicals to their crops, and the list goes well beyond the pesticides that get most of the public attention. The main categories include fertilizers that feed the soil, herbicides that kill weeds, insecticides that target pest species, fungicides that prevent disease, plant growth regulators that shape how a crop develops, and various additives that help all of those products work better. Many of these chemicals are applied before a seed even goes into the ground, and others are used after harvest to keep produce fresh on its way to your grocery store.
Fertilizers That Feed the Crop
The most widely used agricultural chemicals by sheer volume are fertilizers. Nitrogen, phosphorus, and potassium form the “big three” macronutrients that drive plant growth and development, and a deficiency or excess of any one of them directly reduces both yield and quality.1PubMed Central. Optimum Nitrogen, Phosphorous, and Potassium Fertilizer Application Increased Chrysanthemum Growth and Quality by Reinforcing the Soil Microbial Community and Nutrient Cycling Function Most conventional farms rely on synthetic fertilizers manufactured through industrial processes. Nitrogen fertilizers alone, typically in the form of anhydrous ammonia, urea, or ammonium nitrate, account for a massive share of global agrochemical tonnage. Phosphorus and potassium are usually applied as mined and processed mineral salts.
Beyond those three, crops also need micronutrients in smaller amounts: zinc, iron, copper, manganese, boron, and molybdenum among them. These are often delivered through chelated fertilizer formulations, compounds that wrap the metal ion in an organic molecule so the plant can absorb it more easily. A common chelator used in commercial micronutrient fertilizers is EDTA, though it barely breaks down in soil and can leach into groundwater. Newer biodegradable chelators have shown they can outperform EDTA-based products, boosting lettuce biomass by roughly 40 to 60 percent in greenhouse trials while degrading far more readily in the environment.2PubMed. Novel Biodegradable Chelating Agents for Micronutrient Fertilization
Herbicides for Weed Control
Herbicides are the most heavily applied class of pesticides in many countries, particularly in large-scale row-crop farming. They work by targeting specific biological processes in plants. Some block the enzymes that build amino acids. Others bind to proteins involved in photosynthesis, shutting down the plant’s ability to convert sunlight into energy. Still others cause a buildup of toxic light-sensitive molecules inside the weed, or interfere with cell division so the plant cannot grow.3PubMed Central. Overview of herbicide mechanisms of action A separate group of herbicides targets lipid synthesis, making them especially useful against grassy weeds.
Glyphosate remains the world’s most recognized herbicide, largely because of its pairing with genetically modified crops engineered to tolerate it. But it is far from the only one. Farmers choose among dozens of active ingredients depending on the weed species present, the crop being grown, and the stage of the growing season. Pre-emergence herbicides are sprayed on the soil before weeds appear, while post-emergence products are applied after weeds have started growing. Many farmers tank-mix two or more herbicides with different modes of action to reduce the chance of weeds developing resistance.
Insecticides and the Rise of Neonicotinoids
Insecticides protect crops from beetles, aphids, caterpillars, mites, and a long list of other pests. The chemistry has shifted dramatically over the decades, from the now-banned organochlorines of the mid-twentieth century to organophosphates, carbamates, pyrethroids, and more recently neonicotinoids. Neonicotinoids became the fastest-growing class of insecticides in modern crop protection, used widely against both sucking pests like aphids and certain chewing insects. They work by mimicking a natural brain chemical in insects, binding to receptors in the nervous system and causing overstimulation and death, while being far less toxic to mammals at field-relevant doses.4PubMed. Neonicotinoids-from zero to hero in insecticide chemistry
The selectivity that made neonicotinoids popular in farming also made them controversial. Their persistence in soil and their ability to move through a plant’s tissues mean that residues can show up in pollen and nectar, which has raised serious concerns about harm to bees and other pollinators. Several neonicotinoid products have been restricted or banned for outdoor use in the European Union, while remaining widely used in much of the rest of the world.
Fungicides and Disease Prevention
Fungal diseases can devastate crops quickly, and fungicides are a core tool for managing them. Two of the most important chemical families are triazoles and strobilurins. In wheat trials, fungicide treatment protected all plants from root rot during early growth and kept protection above 96 percent through the end of the season, compared to untreated fields where infection climbed from about 8 percent early on to roughly 15 percent by harvest.5PubMed Central. Triazoles and Strobilurin Mixture Affects Soil Microbial Community and Incidences of Wheat Diseases Fungicides are not just about visible disease; they also reduce the levels of mycotoxins, toxic compounds produced by fungi that can contaminate grain and make it unsafe for human or animal consumption.
One trade-off with fungicide use is what happens to the soil microbial community. The same wheat study found that treated soil showed lower microbial diversity overall, even as certain beneficial fungi became more abundant. The disease-causing genus Fusarium dropped to half its previous levels in treated fields, which is the whole point, but the broader shift in soil life is something researchers continue to monitor.
Plant Growth Regulators
Not every chemical a farmer sprays is meant to kill something. Plant growth regulators are compounds that modify how a crop grows, often by shortening stems to prevent lodging (the collapse of tall grain crops in wind or rain). In cotton, growth regulators are used to control excessive leafy growth, promote higher yields, improve fiber quality, and make the plants easier to harvest mechanically.6Agriculture. Management of Plant Growth Regulators in Cotton Using Active Crop Canopy Sensors
In cereal crops like barley and wheat, chemicals such as chlormequat (CCC) and ethephon are applied to stiffen stems. These treatments also tend to increase the number of grain-bearing shoots a plant produces. Barley treated with an early application of chlormequat or ethephon produced more spike-bearing shoots than untreated controls, primarily because more tillers survived to bear grain rather than dying off.7Crop Science. Modification of Tiller Productivity in Spring Barley by Application of Chlormequat or Ethephon Other growth regulators include desiccants that dry down a crop just before harvest, defoliants used in cotton picking, and ethylene-releasing compounds that promote uniform fruit ripening.
Seed Treatments
Many chemicals are applied before the crop is even planted, directly onto the seed. Pre-sowing seed treatment with systemic fungicides is standard practice for most agricultural crops worldwide, intended to protect young seedlings against diseases carried on the seed coat or lurking in the soil.8PubMed Central. Seed Treatment With Systemic Fungicides: Time for Review These coatings are “systemic,” meaning the active ingredient is taken up by the growing plant and distributed through its tissues, providing protection from the inside out during the vulnerable seedling stage.
Seed treatments are not limited to fungicides. Insecticide seed dressings using neonicotinoids like imidacloprid and thiamethoxam are common on crops like groundnuts, corn, and soybeans. Field experiments on groundnut showed that seed treatment with imidacloprid or thiamethoxam at appropriate doses significantly reduced populations of sap-feeding pests like jassids and thrips during the critical early growth window.9Journal of Oilseeds Research. Evaluation of seed dressing chemicals for the management of sucking pests in summer groundnut (Arachis hypogaea L.) The appeal is obvious: treating the seed targets the chemical precisely where the young plant needs it, rather than broadcasting it over the entire field.
Spray Adjuvants and Tank-Mix Additives
Farmers rarely spray a pure pesticide solution. Most tank mixes include adjuvants, additives that improve how the spray behaves. Surfactants lower the surface tension of droplets so they spread across waxy leaf surfaces instead of beading up and rolling off. Drift retardants make droplets heavier so they fall where intended instead of floating away on a breeze. Other additives improve how well the chemical penetrates into plant tissue or slow evaporation in hot conditions.10PubMed Central. Tank-Mix Adjuvants Enhance Pesticide Efficacy by Improving Physicochemical Properties and Spraying Characteristics for Application to Cotton with Unmanned Aerial Vehicles
These adjuvants matter more than they might sound. Better droplet coverage and sticking means the active ingredient actually reaches the pest or weed, and that in turn means farmers can sometimes use lower doses and still get effective control. Research on wheat found that a specific tank-mix adjuvant significantly improved wetting and spreading on leaves and increased the amount of fungicide deposited on the target.11PubMed. Using tank-mix adjuvant improves the physicochemical properties and dosage delivery to reduce the use of pesticides in unmanned aerial vehicles for plant protection in wheat With the growth of drone-based spraying in some regions, getting these formulations right has become even more important because drones use lower spray volumes than traditional equipment.
Soil Fumigants
For high-value crops like strawberries, tomatoes, and peppers, farmers sometimes fumigate the soil before planting. Fumigants are volatile chemicals, often injected or applied under plastic sheeting, that kill nematodes (tiny parasitic worms), fungal pathogens, weed seeds, and insects living in the soil. Methyl bromide was the gold-standard fumigant for decades until it was phased out under international treaty for depleting the ozone layer. Its replacements include chloropicrin, 1,3-dichloropropene, and metam sodium, though none are as broadly effective as methyl bromide was.
Because fumigants tend to kill indiscriminately, wiping out beneficial soil organisms along with the harmful ones, there is growing interest in non-fumigant alternatives. These include targeted nematicides, both chemical and biological, that are considered more environmentally friendly than full-soil fumigation.12PubMed. Effect of fumigants and non-fumigants on nematode and weed control, crop yield, and soil microbial diversity and predicted functionality in a strawberry production system
Biological Alternatives
Not all crop-protection products are synthetic. Biopesticides based on naturally occurring organisms have carved out a significant niche, and the biggest player is Bacillus thuringiensis (Bt), a soil bacterium that produces proteins toxic to certain insect larvae. Bt-based products are the most widely used biopesticides in the world.13PubMed Central. An overview of the production and use of Bacillus thuringiensis toxin They are valued for their specificity: the toxins affect particular groups of insects (caterpillars, beetle larvae, or mosquito larvae, depending on the strain) while being considered safe for mammals, birds, and most beneficial insects.14Egyptian Journal of Biological Pest Control. Bacillus thuringiensis as microbial biopesticide: uses and application for sustainable agriculture
Beyond Bt, the biological toolbox includes fungal biocontrol agents like Trichoderma species, bacterial inoculants that promote root growth, and biochemical pesticides like neem oil. Organic farming systems rely heavily on these products, but conventional farmers use them too, often integrating them with synthetic chemicals in what is called integrated pest management. The push toward biopesticides has been driven partly by the drawbacks of synthetic chemicals, including resistance development and non-target effects on pollinators.15PubMed. Bacillus thuringiensis (Bt)-based biopesticide: Navigating success, challenges, and future horizons in sustainable pest control
Post-Harvest Chemical Treatments
The chemistry does not stop at the farm gate. After harvest, produce is often treated with additional chemicals to extend shelf life and prevent spoilage during transport and storage. These treatments include antimicrobials to suppress bacterial and fungal growth, antioxidants to prevent browning, and wax or edible coatings that slow moisture loss and reduce shriveling. Some fruits are exposed to ethylene gas in controlled ripening rooms, while others are treated with compounds like 1-methylcyclopropene that block the ripening signal and keep fruit firm for weeks longer.16PubMed Central. Postharvest treatments of fresh produce Grains, meanwhile, may be treated with insecticides or fumigants in storage facilities to prevent weevil and moth infestations.
How Residues End Up on Your Plate
If farmers apply all these chemicals, a natural question is how much ends up in the food you eat. Regulatory agencies set maximum residue limits (MRLs) for each pesticide on each crop. These are the legal limits for how much residue can be present at the point of sale. A common misconception is that an MRL represents a safety threshold, meaning anything above it is dangerous. In reality, MRLs are set far below levels of actual health concern. One analysis of the fungicide captan on strawberries, for example, found that the chronic safety level was about 2,000 parts per million, while the legal MRL ranged from just 3 to 20 parts per million, a gap of roughly a hundredfold or more.17Journal of Integrative Agriculture. Pesticide food safety standards as companions to tolerances and maximum residue limits Residues detected above the MRL are considered legal violations, but they are not automatically dangerous.
The European Food Safety Authority uses a similar framework when evaluating new uses for pesticide active ingredients, calculating whether residues in food and animal feed from proposed applications would exceed toxicological reference values. When they do not, the use is considered unlikely to pose a consumer health risk.18PubMed Central. Modification of the existing maximum residue levels and setting of import tolerances for flupyradifurone and DFA in various crops and animal commodities The regulatory process is slow, resource-constrained, and not always up to date with the latest testing methods, something the U.S. EPA itself has acknowledged as a challenge.19PubMed. Enhancing pesticide risk assessment processes at the US Environmental Protection Agency But the basic framework of setting legal limits well below levels of demonstrated harm has been in place for decades.
What Happens When Chemicals Mix in the Soil
Farmers often apply several products in the same season, and these chemicals interact in the soil in ways that are still being studied. One finding that caught researchers’ attention is that when multiple pesticides are present together, their breakdown rates can change. In loamy sand soil, the herbicide iodosulfuron-methyl-sodium had a half-life of about 40 days when applied alone. When applied alongside fungicides, that half-life roughly doubled to about 89 days, meaning the chemical persisted in the soil almost twice as long.20PubMed Central. Changed degradation behavior of pesticides when present in mixtures The implication is that risk assessments based on testing one chemical at a time may underestimate how long residues stick around in real-world field conditions where multiple products are in play.
Pesticide legislation varies greatly around the world, with developed nations generally maintaining more stringent regulations than developing countries, which often lack the resources and expertise to fully implement and enforce their rules. These global differences in pesticide law also create trade barriers, because a crop sprayed legally in one country may exceed the MRL set by an importing country.21PubMed. A review of the global pesticide legislation and the scale of challenge in reaching the global harmonization of food safety standards
Precision Spraying and Reducing Chemical Use
One of the most promising developments in agricultural chemistry is not a new chemical at all but a new way of applying old ones. Precision spraying systems use cameras, sensors, or artificial intelligence to identify exactly where weeds or pests are, then spray only those spots instead of blanketing the whole field. Field trials on sugarcane found that robotic spot spraying was 97 percent as effective as conventional broadcast spraying while reducing herbicide use by about 35 percent on average, and by as much as 65 percent in areas with lighter weed pressure. Runoff measurements showed the mean concentration of herbicides in irrigation water dropped by roughly 39 percent compared to broadcast fields.22arXiv. Precision Robotic Spot-Spraying: Reducing Herbicide Use and Enhancing Environmental Outcomes in Sugarcane
Similar results have been documented in soybean and maize, where real-time sensor-based spraying cut pesticide costs to less than half of what conventional application cost, with no difference in average crop yield.23Scientific Reports. Reduction of pesticide application via real-time precision spraying The reductions were greatest in the early stages of crop growth, when plants are small and there is a lot of bare ground between rows that does not need spraying. As the technology matures and the cost of the equipment comes down, precision application could substantially reshape how many chemicals end up in the environment.
Farmworker Exposure and Protective Equipment
For consumers, pesticide residues on food are the main concern. For the people who actually handle these chemicals, the stakes are more immediate. Farmworkers exposed to pesticides without adequate protection show measurable biological effects, including suppressed activity of an enzyme critical to nerve signaling and elevated markers of inflammation.24PubMed Central. The impact of the use of personal-protective-equipment on the minimization of effects of exposure to pesticides among farm-workers in India When the same workers were provided with basic protective equipment for 90 days, those biomarker levels improved significantly.
Despite this, protective gear use among pesticide handlers worldwide remains uneven. A systematic review found that while about two-thirds of handlers wore long-sleeved shirts and roughly 70 percent wore long trousers, far fewer used the more effective forms of protection: only about 40 percent wore gloves, about a quarter wore goggles, and fewer than 10 percent used aprons.25PubMed. Factors affecting use of personal protective equipment and pesticide safety practices: A systematic review The gap was wider for hired farmworkers compared to farm owners, and education level, income, and access to training programs were among the strongest predictors of whether someone used proper protection. In Indonesian farming communities, roughly 89 percent of workers who used protective equipment were categorized as healthy, while those who did not had significantly higher rates of symptoms like dizziness, blurred vision, and difficulty breathing.26PubMed Central. Pesticide Poisoning and the Use of Personal Protective Equipment (PPE) in Indonesian Farmers The chemistry matters, but so does how it is handled on the ground.