Geraniol
A plant-derived monoterpene alcohol used against plant-parasitic nematodes, mites and mildew. What the research shows, why contact matters far more than vapour, and why it must be kept away from cats.
What is geraniol?
Geraniol is a monoterpene alcohol found in rose, palmarosa, citronella, geranium and lemongrass, occurring in over 250 essential oils. In agriculture it acts as a contact nematicide, acaricide and fungicide. In cosmetics and household products it appears as a fragrance component — and is one of the twenty-six fragrance substances the EU requires to be declared, because it is a recognised contact allergen. Same molecule, three very different readerships.
Also known as trans-geraniol, lemonol, (E)-3,7-dimethylocta-2,6-dien-1-ol. CAS 106-24-1.
What it is used against
- root-knot nematode (Meloidogyne)
- lesion nematode
- spider mite
- two-spotted mite
- powdery mildew
- jumping worm (Amynthas spp.)
- slugs
- snails
How does geraniol work?
Geraniol acts on contact. It is lipophilic enough to partition into the cuticle and membranes of soft-bodied organisms, disrupting membrane integrity and the ion gradients that depend on it. In nematodes the result is rapid paralysis and loss of motility; in mites, membrane disruption and desiccation. Comparative screens found monoterpenoids carrying hydroxyl or carbonyl groups consistently more active than those without, which helps explain why geraniol outperforms structurally similar terpenes lacking them.
It is not systemic. It does not translocate within the plant and it does not persist — which means it must physically reach the target, and leaves very little residue.
What does the research show?
In a comparative screen of 22 monoterpenoids against Meloidogyne incognita, geraniol ranked among the most active compounds. At 250 mg/L, 20 of 22 reduced egg hatching and 11 reduced second-stage juvenile mobility.
Work on Meloidogyne javanica found a dose-dependent effect on both egg hatch and juvenile viability, with geraniol paralysing effectively all second-stage juveniles on contact and inhibiting egg hatch by roughly 70%.
The most operationally useful finding is the difference between exposure routes: direct contact produced near-total juvenile mortality while vapour-phase exposure produced only around 10%. Geraniol is not a fumigant. Whatever brings it into physical contact with the nematode in the root zone — water volume, soil moisture, distribution, formulation — is doing most of the work.
What does geraniol not do?
It will not fumigate a soil profile. It is not systemic and offers no protection to root growth produced after the active has degraded. It does not eradicate an established population — expectations should be framed as population reduction and reduced galling. It is not target-site selective, so soft-bodied non-target organisms in the treated zone can be affected, which argues for targeted placement over broadcast use. And against powdery mildew it performs as a protectant, not an eradicant on established infection.
- soil fumigation — vapour-phase activity is weak (~10% vs near-total mortality on contact)
- protection of root growth produced after the active degrades — not systemic
- eradication of an established nematode population — expect reduction, not elimination
- established powdery mildew infection — acts as protectant, not eradicant
What conditions change the outcome?
Volatile and degraded by warmth and light, which keeps residues low and limits persistence. Soil moisture governs distribution: too dry and it will not reach the root zone, waterlogged and it is diluted. Organic matter binds monoterpenes, so high-organic soils need attention to distribution rather than simply more product. For foliar use coverage is everything, since activity is by contact.
Safety — read this if you have a cat
Geraniol is toxic to cats, and this is not a precaution that can be softened. Cats lack adequate activity of UDP-glucuronosyltransferase, the pathway mammals principally use to conjugate and excrete phenolic and terpenoid compounds, so terpenes accumulate rather than clear. Essential oils are absorbed readily across the gastrointestinal tract, skin, lungs and mucous membranes, so exposure does not require ingestion, and grooming makes cats especially vulnerable.
Reported signs of essential-oil toxicosis range from vomiting, diarrhoea, lethargy and skin irritation through to tremors, low blood pressure, bradycardia, hypothermia, seizures, hind-limb weakness and hepatic or renal failure.
Geraniol products must never be applied to a cat, and treated areas should be dry and ventilated before a cat has access. Some third-party products do market geraniol for veterinary use on cats; the metabolic evidence argues against it, and Vegalab's position is that no product on this platform is for on-animal use. If you suspect exposure, contact a veterinarian or poison-control service now. This page is not veterinary advice. Peppermint oil carries the same caution for the same reason.
The ratings below use the same vocabulary as the Safety & Stewardship section, so a reader sees one set of terms across the site.
| Who or what | Rating | Why |
|---|---|---|
| Cats | avoid | Cats lack adequate UDP-glucuronosyltransferase activity, the pathway mammals principally use to conjugate and excrete phenolic and terpenoid compounds, so terpenes accumulate rather than clear. Absorption occurs across the gastrointestinal tract, skin, lungs and mucous membranes, so exposure does not require ingestion, and grooming makes cats especially vulnerable. Never apply to a cat. Treated areas must be dry and ventilated before access. |
| Dogs | caution | Metabolise terpenes more effectively than cats but are not immune. Same avoid-during-application and dry-before-access approach. |
| Bees and pollinators | caution | Contact material with short persistence, so timing is the main lever. Avoid application to open bloom and to foraging periods; prefer late-day treatment where bees are active. |
| Fish and aquatic life | avoid | Monoterpenes are generally harmful to fish at low concentrations. Keep applications and rinsate out of ponds, ditches and drains. |
| Children | caution | Standard label precautions; store out of reach. |
| Edible crops | ok | Low residue and rapid degradation. Follow the label pre-harvest interval. |
| Applicator | caution | Undiluted geraniol is a skin and eye irritant. Natural origin does not remove the need for gloves, eye protection and ventilation when handling concentrate. |
Do not expose — cats. Cats lack adequate UDP-glucuronosyltransferase activity, the pathway mammals principally use to conjugate and excrete phenolic and terpenoid compounds, so terpenes accumulate rather than clear. Absorption occurs across the gastrointestinal tract, skin, lungs and mucous membranes, so exposure does not require ingestion, and grooming makes cats especially vulnerable. Never apply to a cat. Treated areas must be dry and ventilated before access.
If you think a cat has been exposed, contact a veterinarian or a poison-control service now rather than waiting for signs to develop. This page is not veterinary or medical advice.
Do not expose — fish. Monoterpenes are generally harmful to fish at low concentrations. Keep applications and rinsate out of ponds, ditches and drains.
Contact your environmental regulator immediately if product reaches a watercourse. This page is not veterinary or medical advice.
What other safety considerations apply?
Dogs metabolise terpenes better than cats but are not immune. For pollinators, short persistence makes timing the main lever — avoid open bloom and foraging periods. Monoterpenes are generally harmful to fish at low concentrations, so keep applications and rinsate out of watercourses. Undiluted geraniol is a skin and eye irritant: natural origin does not remove the need for gloves, eye protection and ventilation.
What is its regulatory status?
Geraniol appears on the US EPA list of active ingredients eligible for the minimum-risk (FIFRA 25(b)) exemption, but exemption applies to a complete formulated product meeting every condition of the rule — including that all inerts appear on the permitted list — not to the active in isolation. Exempt status must be confirmed product by product, as must OMRI listing. Status differs by jurisdiction; always follow the applicable label.
| Framework | Status | What that means |
|---|---|---|
| US FIFRA 25(b) | active-eligible | Appears on the EPA list of actives eligible for the minimum-risk exemption, but exemption applies to a complete formulated product meeting every condition of the rule, including that all inerts appear on the permitted list. |
| OMRI | per-product | Attaches to specific products, not to the compound. State only where confirmed for that product. |
| EU cosmetics | declarable-allergen | One of the 26 fragrance substances the EU requires to be declared on cosmetic labels. This is a sensitisation statement, not acute toxicity. |
| Other jurisdictions | unverified | Registration, permitted uses and claims vary by jurisdiction. |
Which products are built on geraniol?
Listed for reference, not as a recommendation. Nematode Control (soil-applied, plant-parasitic nematodes including root-knot) · Mildew Control (geraniol 17%, foliar, powdery mildew) · Spider Mite Control (geraniol 30% with peppermint, cottonseed and rosemary oils) · Jumping Worm Control (with plant-derived saponins and bio-surfactants) · Vetpure Miticide in Biosecurity, for animal premises and not for on-animal use.
- Nematode Control — soil-applied
- Mildew Control (17%) — foliar
- Spider Mite Control (30%) — with peppermint, cottonseed and rosemary oils
- Jumping Worm Control — with plant-derived saponins and bio-surfactants
- Vetpure Miticide — Biosecurity — animal premises only, NOT for on-animal use
Related problems in the Pest & Disease Library
References
- Nematicidal activity of monoterpenoids against the root-knot nematode Meloidogyne incognita — Independent · in vitro screen of 22 monoterpenoids at 250 mg/L
- Effect of geraniol, a plant-based alcohol monoterpene oil, against Meloidogyne javanica — European Journal of Plant Pathology, 2018 · contact vs vapour comparison
- A Comprehensive in vitro and in silico Analysis of Nematicidal Action of Essential Oils — Frontiers in Plant Science, 2020 · open access
- A combination of plant-based compounds and extracts acts nematicidal and induces resistance against Meloidogyne incognita in tomato — Frontiers in Plant Science, 2024 · open access
- Toxicoses From Essential Oils in Animals — Merck Veterinary Manual · clinical reference
- Geranium is toxic to cats — Pet Poison Helpline