Organic farmers use a range of pesticides derived from natural sources, along with a short list of approved synthetic substances. The common assumption that organic means pesticide-free is wrong. What it actually means is that organic operations must rely on prevention first and turn to approved pesticides only as a last resort, choosing from a federally regulated list of natural and synthetic options.
Prevention Comes Before Any Spray
The USDA’s National Organic Program requires farmers to treat chemical pest control as their final option, not their first. The mandated hierarchy starts with preventive measures: crop rotation, building healthy soil, choosing disease-resistant varieties, and managing nutrients to help plants defend themselves naturally. If pests still show up, farmers move to physical and mechanical controls like hand-weeding, row covers, and tillage.
Only after those steps fail can an organic farmer reach for a pesticide. And even then, they’re required to choose the most effective, least disruptive option available. This layered approach is a core distinction from conventional farming, where synthetic pesticides can be applied as a routine preventive measure from the start.
Botanical Pesticides
Some of the most widely used organic pesticides come directly from plants. These break down relatively quickly in the environment compared to many synthetic alternatives, which is a major reason they’re permitted.
Pyrethrins, extracted from chrysanthemum flowers, work against a broad range of insects and mites, including spider mites, flies, fleas, and beetles. They disrupt the insect’s nervous system by interfering with the electrical signals that control movement, causing paralysis and death. Pyrethrins degrade rapidly in sunlight, which limits their environmental persistence but also means timing the application matters.
Neem oil, derived from the neem tree, takes a different approach. Its active compound works primarily as a feeding deterrent and growth disruptor. Instead of killing insects on contact, it blocks hormones that insects need to develop from one life stage to the next. Caterpillars stop feeding, larvae fail to molt. It’s effective against aphids, caterpillars, thrips, and mealybugs, among others.
Sabadilla, made from the seeds of a lily-like plant, acts on the nervous system similarly to pyrethrins. It’s used primarily against stink bugs, squash bugs, thrips, leafhoppers, and caterpillars.
Microbial Pesticides
These are living organisms, or substances derived from them, that target specific pest groups. They tend to be highly selective, which means they leave beneficial insects largely unharmed.
Bt (Bacillus thuringiensis) is a soil bacterium that produces proteins toxic to insect larvae. Different strains target different pests. One variety kills caterpillars (moth and butterfly larvae), while another targets fly larvae, including mosquitoes. Bt only affects insects that eat it, so it poses minimal risk to pollinators and predatory insects that don’t feed on treated foliage.
Spinosad comes from another soil bacterium and is broader in its reach. It controls caterpillars, leaf miners, flies, thrips, beetles, and spider mites. Because of this wider spectrum, organic farmers use it when pest pressure involves multiple species at once.
Mineral-Based Fungicides and Insecticides
Copper and sulfur are the workhorses of organic disease control, and both have been used in agriculture for well over a century.
Several forms of copper are approved for organic use: copper sulfate, copper hydroxide, copper oxide, and copper oxychloride. When copper sulfate is mixed with calcium hydroxide, it becomes Bordeaux mixture, a classic fungicide still used on grapes, tomatoes, and stone fruits. Copper products control fungal and bacterial diseases like downy mildew, late blight, and fire blight.
The catch with copper is that it doesn’t break down. It’s an element, so repeated applications cause it to accumulate in soil over time. Research on organic farms in southern Italy found medium-level copper buildup in soils, prompting calls for stricter enforcement of existing limits and a shift toward copper alternatives where possible. The European Union caps copper use at 4 kilograms per hectare per year for organic operations, though the U.S. doesn’t impose a comparable hard limit.
Elemental sulfur pulls double duty as both a fungicide and an insecticide. It controls powdery mildew and other fungal diseases while also working against mites. Lime sulfur, a liquid form made by combining sulfur with calcium hydroxide, serves similar purposes and is particularly common in orchards during the dormant season.
Approved Synthetic Substances
The word “organic” doesn’t mean zero synthetics. The USDA maintains a National List of synthetic substances specifically permitted in organic crop production. The list is short and tightly controlled, with each substance reviewed every five years.
For insect control, the approved synthetics include insecticidal soaps, horticultural oils (narrow-range petroleum-based oils that smother soft-bodied insects), and sticky traps. Boric acid is allowed, but only for structural pest control, not on crops. Ammonium carbonate can be used as bait inside insect traps. Ferric phosphate is approved as a slug and snail bait, and vitamin D3 is the only permitted rodenticide.
For sanitation and disease prevention, organic farmers can use chlorine materials (sodium hypochlorite, chlorine dioxide, and related compounds), hydrogen peroxide, and peracetic acid. Potassium bicarbonate is approved for crop disease control. Soap-based herbicides are allowed only for farmstead maintenance and ornamental areas, not for weed control in production fields. Even petroleum-based plastic mulch is technically on the approved list, provided it isn’t made from PVC and is removed at season’s end.
How Organic Pesticide Residues Compare
The practical result of these restrictions shows up in measurable ways. Multiple clinical studies have tracked pesticide metabolites in urine after people switched between conventional and organic diets. In one study, children’s pesticide metabolite levels dropped to undetectable within days of switching to organic food. Another found that overall pesticide residues during an organic diet phase were 89% lower than during the conventional phase. A study comparing children’s diets found that those eating conventional food had six times higher median concentrations of organophosphorus pesticide metabolites than those eating organic.
This doesn’t mean organic produce is residue-free. Drift from neighboring conventional farms, shared equipment, and the organic pesticides themselves can all leave traces. But the volume and variety of residues are consistently and substantially lower.
Natural Doesn’t Automatically Mean Safer
One important nuance: “natural origin” and “low toxicity” aren’t the same thing. Rotenone, a botanical insecticide once widely used in organic farming (now restricted or banned in many places), was more acutely toxic to mammals than some synthetic alternatives it was meant to replace. Copper fungicides, while naturally occurring, are toxic to aquatic organisms and accumulate in soil permanently.
That said, many of the most hazardous synthetic pesticides historically used in conventional agriculture have acute toxicity levels far exceeding anything on the organic-approved list. Older synthetic organochlorines like endrin had rat oral toxicity values as low as 3 mg/kg, meaning an extremely small dose was lethal. By comparison, neem oil’s active compound has a toxicity value around 3,540 mg/kg, making it roughly a thousand times less acutely toxic by that measure.
The more meaningful safety advantage of most organic pesticides is their persistence. Pyrethrins break down in hours to days. Bt proteins degrade in sunlight. Neem compounds lose effectiveness within a week or two. Many synthetic pesticides, particularly older ones, can persist in soil and water for months or years. This shorter environmental lifespan reduces long-term accumulation in ecosystems, even if the organic product requires more frequent application.