Prohibited Substance
A substance not allowed in organic production under the National Organic Program. Includes most synthetic pesticides, fertilizers, and growth regulators.
A prohibited substance in organic certification is any material that may not be used in producing or handling organic agricultural products. Under NOP §205.105, the default rule is:
- Synthetic substances are prohibited unless specifically allowed by the National List
- Natural substances are allowed unless specifically prohibited by the National List
The National List of Allowed and Prohibited Substances (NOP §205.601 through §205.606) is the authoritative source. See the dedicated National List entry.
Examples
The most common prohibited substances on a working farm:
- Synthetic fertilizers — urea, anhydrous ammonia, triple superphosphate, most blended NPK products
- Synthetic pesticides — glyphosate, atrazine, neonicotinoids, most conventional herbicides and insecticides
- Synthetic growth regulators — ethephon, mepiquat chloride
- Sewage sludge / biosolids — prohibited even though "natural"
- GMO seed and inoculants — prohibited under NOP §205.105(e) (excluded methods)
- Most ionizing radiation treatments — prohibited under NOP §205.105(f)
For livestock specifically: most synthetic parasiticides, hormones for growth promotion, and antibiotics are prohibited (with very limited exceptions). See NOP §205.604.
What "applied" means
A substance is "applied" if it's deliberately brought into contact with the certified land or product, OR if it migrates onto the parcel through drift, runoff, or contamination. Drift from a neighbor counts. Runoff from a public road does not necessarily, depending on circumstance.
The OSP must describe both deliberate avoidance (don't use prohibited inputs) and contamination prevention (buffer zones, equipment cleaning, signage).
Why operations care
Application of a prohibited substance — even accidentally, even by someone else — typically resets the 36-month transition clock for the affected parcel and can result in immediate suspension of certification for that land.
Quick Organics + prohibited substances
When health records are entered for livestock in Quick Organics, the system checks the substance against the National List and flags prohibited substances with a red marker visible to both the farmer and the certifier. The Master Herd List surfaces these flags in the certifier's read-only view so issues are caught early.
Cited regulations
Linked to the current eCFR text of 7 CFR Part 205. Reviewed before publication.
QO Editorial Team
Quick Organics
Quick Organics' editorial team writes about USDA organic certification, the Organic System Plan, and the daily realities of running a certified organic operation. Material is reviewed against the current eCFR text of 7 CFR Part 205 before publication.