Paclobutrazol (Ref: PP 333)

Paclobutrazol (Ref: PP 333)	Last updated: 25/05/2025
(Also known as: paclobutrazole)

SUMMARY

Data alerts

The following alerts are based on the data in the tables below. An absence of an alert does not imply the substance has no implications for human health, biodiversity or the environment but just that we do not have the data to form a judgement.

Environmental fate	Ecotoxicity	Human health
Environmental fate Moderate alert: GUS: Transition state; Drainflow: Moderately mobile	Ecotoxicity Moderate alert: Birds chronic ecotoxicity: Moderate; Fish acute ecotoxicity: Moderate; Fish chronic ecotoxicity: Moderate; Daphnia acute ecotoxicity: Moderate; Daphnia chronic ecotoxicity: Moderate; Bees acute contact ecotoxicity: Moderate; Bees acute oral ecotoxicity: Moderate; Earthworms acute ecotoxicity: Moderate; Earthworms chronic ecotoxicity: Moderate	Human health Moderate alert: Mammals acute toxicity: Moderate; Mammals chronic toxicity: Moderate; Reproduction/development effects

GENERAL INFORMATION

Description

A conazole plant growth regulator with some mild fungicidal activity for ornamentals, fruit and other crops to inhibit vegetative growth

Example pests controlled

Growth - reduces internodal elongation to improve plant shape

Example applications

Mango; Cotton; Corn; Chilli; Bonzi production; Grape vines

Efficacy & activity

Availability status

Current

Introduction & key dates

1986, introduced

GB regulatory status

GB COPR regulatory status

Approved

Date COPR inclusion expires

30/09/2027

GB LERAP status

Check label - may vary with formulation

EC Regulation 1107/2009 (repealing 91/414)

EC Regulation 1107/2009 status

Approved

Dossier rapporteur/co-rapporteur

Austria/Romania

Date EC 1107/2009 inclusion expires

31/08/2026

EU Candidate for substitution (CfS)

Yes - two 'Persistent-Bioaccumulative-Toxic' criteria

Listed in EU database

Yes

Approved for use (✓) under EC 1107/2009 in the following EU Member States

ATAustria	BEBelgium	BGBulgaria	CYCyprus	CZCzech Republic	DEGermany	DKDenmark	EEEstonia	ELGreece
✓	✓	✓	✓	✓	✓	✓	✓	✓
ESSpain	FIFinland	FRFrance	HRCroatia	HUHungary	IEIreland	ITItaly	LTLithuania	LULuxembourg
✓	✓	✓		✓	✓	✓	✓
LVLatvia	MTMalta	NLNetherlands	PLPoland	PTPortugal	RORomania	SESweden	SISlovenia	SKSlovakia
✓		✓	✓	✓	✓	✓		✓

Approved for use (✓) under EC 1107/2009 by Mutual Recognition of Authorisation and/or national regulations in the following EEA countries

ISIceland	NONorway
	✓

Additional information

Also used in

Australia

Chemical structure

Isomerism

A molecule with two chiral centres. The technical material is a racemate comprising equimolar amounts of (2R,3R)- and (2S,3S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)pentan-3-ol.

Chemical formula

C₁₅H₂₀ClN₃O

Canonical SMILES

CC(C)(C)C(C(CC1=CC=C(C=C1)Cl)N2C=NC=N2)O

Isomeric SMILES

CC(C)(C)[C@H]([C@@H](CC1=CC=C(C=C1)Cl)N2C=NC=N2)O

International Chemical Identifier key (InChIKey)

RMOGWMIKYWRTKW-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/2C15H20ClN3O/c2*1-15(2,3)14(20)13(19-10-17-9-18-19)8-11-4-6-12(16)7-5-11/h2*4-7,9-10,13-14,20H,8H2,1-3H3/t2*13-,14-/m10/s1

2D structure diagram/image available?

Yes

General status

Pesticide type

Plant Growth Regulator; Herbicide

Substance groups

Triazole herbicide; Triazole PGR

Minimum active substance purity

930 g kg⁻¹

Known relevant impurities

EU dossier - None declared

Substance origin

Synthetic

Mode of action

Absorbed through leaves, stem and roots and translocated. Gibberellin biosynthesis inhibitor

CAS RN

76738-62-0

EC number

616-379-6

CIPAC number

445

US EPA chemical code

125601

PubChem CID

73671

CLP index number

603-239-00-4

Molecular mass

293.8

PIN (Preferred Identification Name)

IUPAC name

(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)pentan-3-ol

CAS name

(αR,βR)-rel-β-((4-chlorophenyl)methyl)-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol

Other status information

Possible groundwater pollutant

Relevant Environmental Water Quality Standards

Herbicide Resistance Class (HRAC MoA class)

Not applicable

Herbicide Resistance Class (WSSA MoA class)

Not applicable

Insecticide Resistance Class (IRAC MoA class)

Not applicable

Fungicide Resistance Class (FRAC MOA class)

Not applicable

Examples of recorded resistance

Physical state

White to beige coloured crystalline solid

Formulations

Property

Value

Example manufacturers & suppliers of products using this active now or historically

Agrovista
Fine
Syngenta
BOC Sciences

Example products using this active

Bonzi
Cultar
Parlay
Piroutte

Formulation and application details

Often supplied as a suspension concentrate that is mixed with water and used as a spray

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

Solubility - In water at 20 °C (mg l⁻¹)

22.9

Moderate

Solubility - In organic solvents at 20 °C (mg l⁻¹)

72400

Acetone

5670

Xylene

150000

Methanol

199

n-Heptane

Melting point (°C)

164

Boiling point (°C)

384

Degradation point (°C)

Flashpoint (°C)

Octanol-water partition coefficient at pH 7, 20 °C

1.29 X 10⁰³

Calculated

Log P

3.11

High

Fat solubility of residues

Solubility

Likely to be soluble

Data type

Based on chemical group

Density (g ml⁻¹)

1.23

Dissociation constant pKa) at 25 °C

Vapour pressure at 20 °C (mPa)

0.0019

Low volatility

Henry's law constant at 25 °C (Pa m³ mol⁻¹)

2.39 X 10^-05

Non-volatile

Volatilisation as max % of applied dose lost

From plant surface

From soil surface

Maximum UV-vis absorption L mol⁻¹ cm⁻¹

Neutral solution: 222nm = 10900, 260nm = 233, 267nm = 294, 276nm = 236
Acidic solution: 221nm = 17500, 260nm = 228, 267nm = 284, 276nm = 229
Basic solution: 221nm = 12800, 260nm = 222, 267nm = 280, 276nm = 225
No absorbance > ca 280nm

Surface tension (mN m⁻¹)

66.0

at 20.5 °C]

Degradation

Property

Value

Source; quality score; and other information

Interpretation

General biodegradability

Soil degradation (days) (aerobic)

DT₅₀ (typical)

112

Persistent

DT₅₀ (lab at 20 °C)

120

Persistent

DT₅₀ (field)

29.5

Non-persistent

DT₉₀ (lab at 20 °C)

577.5

Very persistent

DT₉₀ (field)

98.1

DT₅₀ modelling endpoint

Note

EU dossier lab studies DT₅₀ range 27.1-618 days (normalised), DT₉₀ range 143-2053 days, field studies DT₅₀ range 27.2-60.8 days (normalised), DT₉₀ range 46.7-202 days; Other studies: DT₅₀ (1) lab 84-140 days, field 6-13 months (B4), (2) US sources: 200 days (DW4)

Dissipation rate RL₅₀ (days) on plant matrix

Value

4.4

Note

Wheat, whole plant, n=1

Dissipation rate RL₅₀ (days) on and in plant matrix

Value

6.0

Note

OSR, whole plant, n=1

Aqueous photolysis DT₅₀ (days) at pH 7

Value

Stable

Note

Aqueous hydrolysis DT₅₀ (days) at 20 °C and pH 7

Value

Stable

Note

Stable pH 4 to pH 9 over 30 days at 25 °C

Water-sediment DT₅₀ (days)

787

Stable

Water phase only DT₅₀ (days)

164

Stable

Sediment phase only DT₅₀ (days)

Air degradation

As this parameter is not normally measured directly, a surrogate measure is used: ‘Photochemical oxidative DT₅₀’. Where data is available, this can be found in the Fate Indices section below.

Decay in stored produce DT₅₀

Soil adsorption and mobility

Property

Value

Source; quality score; and other information

Interpretation

Linear

K_d (mL g⁻¹)

Moderately mobile

K_oc (mL g⁻¹)

400

Notes and range

Freundlich

K_f (mL g⁻¹)

4.3

Moderately mobile

K_foc (mL g⁻¹)

210

¹/_n

0.93

Notes and range

EU dossier kf range 0.68-15.1 mL g⁻¹, K_foc range 34.7-665.3 mL g⁻¹, ¹/_n range 0.87-0.97, Soils=13

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

2.47

Calculated

Transition state

SCI-GROW groundwater index (μg l⁻¹) for a 1 kg ha⁻¹ or 1 l ha⁻¹ application rate

Value

1.33 X 10^-01

Calculated

Note

Potential for particle bound transport index

Low

Calculated

Potential for loss via drain flow

Moderately mobile

Calculated

Photochemical oxidative DT₅₀ (hrs) as indicator of long-range air transport risk

7.65

Calculated using the Atkinson method. Assumed 1.5E+06 OH/cm³, 12 hr

Below the level of concern for long-range air transport

Bio-concentration factor

BCF (l kg⁻¹)

Low potential

CT₅₀ (days)

Not available

Known soil metabolites

Metabolite

Major/Minor fraction

$Click here for further information on Major/Minor fraction$

Estimated maximum occurrence fraction

Notes

1H-1,2,4-triazol-1-ylacetic acid (Ref: CGA 142856)

Minor fraction

1,4-dihydro-1,2,4-triazol-5-one (Ref: NOA 457654)

Major fraction

0.251

CAS 930-33-6; Syngenta verified

(2RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)pentan-3-one (Ref: CGA 149907)

Major fraction

0.263

CAS 63190-87-4; Syngenta verifird

1,2,4-triazole (Ref: CGA 71019)

Minor fraction

0.03

Known groundwater metabolites

None

Other known metabolites

Metabolite name and reference

Aliases

Formation medium / Rate

Estimated maximum occurrence fraction

2-amino-3-1,2,4-triazole-1-yl-propionic acid (Ref: CGA 131013)

triazole alanine

Plant

3-hydroxy-1H-1,2,4-triazole, hydroxy triazole (Ref: NOA 457654)

Surface water; Sediment

(2S,3S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)-pentan-3-ol (Ref: R112526)

hydroxy ketone

Surface water; Sediment; Animal commodities

5-(4-chlorophenyl)-2,2-dimethyl-4-(1,2,4-triazol-1-yl)pentane-1,3-diol (Ref: SYN 536408)

diol

Surface water; Sediment

2-hydroxy-3-[1,2,4]-triazole-1-yl-propionic acid (Ref: CGA 205369)

triazole lactic acid

Plant

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

1336

Rat

Moderate

Mammals - Short term dietary NOEL

(mg kg⁻¹)

2.5

Rat

High

(ppm diet)

Mammals - Chronic 21d NOAEL (mg kg⁻¹ bw d⁻¹)

> 117

Rat Reproductive NOAEL

Moderate

Birds - Acute LD₅₀ (mg kg⁻¹)

> 2100

Colinus virginianus

Low

Birds - Short term dietary (LC₅₀/LD₅₀)

> 2000 mg kg feed⁻¹

Colinus virginianus

Birds - Chronic 21d NOEL (mg kg⁻¹ bw d⁻¹)

118.6

Anas platyrhynchos

Moderate

Earthworms - Acute 14 day LC₅₀ (mg kg⁻¹)

> 500

Eisenia foetida corr

Moderate

Earthworms - Chronic NOEC, reproduction (mg kg⁻¹)

0.845

Eisenia foetida corr

Moderate

Soil micro-organisms

Nitrogen mineralisation: No significant adverse effect at 77 days
Carbon mineralisation: No significant adverse effect at 21 days

Dose: 20 kg ha⁻¹

Collembola

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

Non-target plants

58.3

Tomato
Seedling emergence, ER₅₀
as g ha⁻¹

Honeybees (Apis spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

> 40

Apis mellifera

Moderate

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

> 2

Apis mellifera

Moderate

Unknown mode acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Chronic

Notes

Bumblebees (Bombus spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Mason bees (Osmia spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Other bee species (1)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Other bee species (2)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Beneficial insects (Ladybirds)

Beneficial insects (Lacewings)

3.9% Mortality at dose 250 g l⁻¹

Chrysoperla carnea

Beneficial insects (Parasitic wasps) as Mortality LR₅₀ g ha⁻¹ 48 hr

16.7

Aphidius rhopalosiphi

Beneficial insects (Predatory mites) as Mortality LR₅₀ g ha⁻¹ 7 day

> 1000

Typhlodromus pyri

Beneficial insects (Ground beetles)

0% Mortality at dose >1 kg ha⁻¹

Poecilus cupreus

Aquatic ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Temperate Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

23.6

Lepomis macrochirus

Moderate

Temperate Freshwater Fish - Chronic 21 day NOEC (mg l⁻¹)

3.3

Salmo gairdneri

Moderate

Tropical Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

> 18.76

Danio rerio

Moderate

Temperate Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

33.2

Daphnia magna

Moderate

Temperate Freshwater Aquatic invertebrates - Chronic 21 day NOEC (mg l⁻¹)

0.32

Daphnia magna

Moderate

Tropical Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

Aquatic crustaceans - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, static, water (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, sediment (mg kg⁻¹)

Aquatic plants (free-floating, growth) - Acute 7 day EC₅₀, biomass (mg l⁻¹)

0.0082

Lemna gibba

High

Aquatic plants (rooted, growth) - Acute 14 day EC₅₀, biomass (mg l⁻¹)

0.075

Myriophyllum spicatum 28d NOEC

Moderate

Algae - Acute 72 hour EC₅₀, growth (mg l⁻¹)

7.2

Pseudokirchneriella subcapitata

Moderate

Algae - Chronic 96 hour NOEC, growth (mg l⁻¹)

Mesocosm study data

NOEAEC mg l⁻¹

Marine bivalves

HUMAN HEALTH AND PROTECTION

General

Property

Value

Source; quality score; and other information

Interpretation

Threshold of Toxicological Concern (Cramer Class)

High (class III)

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

1336

Rat

Moderate

Mammals - Dermal LD₅₀ (mg kg⁻¹ body weight)

2000

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

3.13

Rat 4 hr (nose only)

Other Mammal toxicity endpoints

ADI - Acceptable Daily Intake (mg kg⁻¹ bw day⁻¹)

0.022

ARfD - Acute Reference Dose (mg kg⁻¹ bw day⁻¹)

0.1

SF=100

AAOEL - Acute Acceptable Operator Exposure Level (mg kg⁻¹ bw day⁻¹)

AOEL - Acceptable Operator Exposure Level - Systemic (mg kg⁻¹ bw day⁻¹)

0.1

SF=100

Dermal penetration studies (%)

Dangerous Substances Directive 76/464

Exposure Routes

Public

No unacceptable risks to bystanders identified

Occupational

No unacceptable risks to operators or other workers identified

MRLs

European

EU MRL pesticide database

Great Britain

GB MRL Register

Notes

Drinking Water Standards

Drinking Water MAC (μg l⁻¹)

0.1

EU Dir 89/778/EC limit; Calc MAC=300 µg l⁻¹

Mammalian dose elimination route and rate

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

; ; ; ;

No data found

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

Respiratory tract irritant

Skin irritant

Skin sensitiser

No data found

Eye irritant

Phototoxicant

No data found

General human health issues

Harmful if inhaled or swallowed

Handling issues

Property

Value and interpretation

General

Not explosive or oxidising
IMDG Transport Hazard Class 4.1
Flammable
Not expected to auto-ignite

CLP classification 2013

Health: H302, H312, H319, H332, H361
Environment: H400, H410
Handling: H228

WHO Classification

II (Moderately hazardous)

UN Number

UN1325

Waste disposal & packaging

Packaging Group II (moderate danger)

Shelf-life, storage, stability and reactivity

Limited shelf-life. Store at 2-8 DegC

TRANSLATIONS

Language

Name

English

paclobutrazol

French

paclobutrazol

German

Paclobutrazol

Danish

paclobutrazol

Italian

paclobutrazolo

Spanish

paclobutrazol

Greek

Polish

paklobutrazol

Swedish

Hungarian

paklobutrazol

Dutch

paclobutrazool

Norwegian

paklobutrazol

Record last updated:	25/05/2025
Contact:	aeru@herts.ac.uk
Please cite as:	Lewis, K.A., Tzilivakis, J., Warner, D. and Green, A. (2016) An international database for pesticide risk assessments and management. Human and Ecological Risk Assessment: An International Journal, 22(4), 1050-1064. DOI: 10.1080/10807039.2015.1133242