Maleic hydrazide

Maleic hydrazide	Last updated: 25/05/2025
(Also known as: maleic hydrazide acid ; MH; Hydrazide)

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 High alert: Drainflow: Mobile	Ecotoxicity Moderate alert: Fish chronic ecotoxicity: Moderate; Daphnia chronic ecotoxicity: Moderate	Human health High alert: Neurotoxicant

GENERAL INFORMATION

Description

A plant growth regulator used to suppress growth in a wide variety of crops

Example pests controlled

Growth - suppression of suckers, sprouts, and to induce dormancy

Example applications

Lawns; Amenity turf; Non-cropped areas; Fruit including citrus; Potatoes; Carrots; Onions, shallots & garlic; Tobacco; Ornamental shrubs

Efficacy & activity

Availability status

Current

Introduction & key dates

post-1950, introduced

GB regulatory status

GB COPR regulatory status

Approved

Date COPR inclusion expires

31/10/2032

GB LERAP status

None

EC Regulation 1107/2009 (repealing 91/414)

EC Regulation 1107/2009 status

Approved

Dossier rapporteur/co-rapporteur

Denmark/Belgium

Date EC 1107/2009 inclusion expires

31/10/2032

EU Candidate for substitution (CfS)

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; USA; Morocco

Chemical structure

Isomerism

None

Chemical formula

C₄H₄N₂O₂

Canonical SMILES

C1=CC(=O)NNC1=O

Isomeric SMILES

No data

International Chemical Identifier key (InChIKey)

BGRDGMRNKXEXQD-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C4H4N2O2/c7-3-1-2-4(8)6-5-3/h1-2H,(H,5,7)(H,6,8)

2D structure diagram/image available?

Yes

Cambridge Crystallographic Data Centre diagrams

Common Name	Relationship	Link
maleic hydrazide	-

General status

Pesticide type

Plant Growth Regulator; Herbicide

Substance groups

Pyridazine PGR

Minimum active substance purity

979 g kg⁻¹

Known relevant impurities

EU dossier - Hydrazine 0.028 mg kg⁻¹

Substance origin

Synthetic

Mode of action

Suppresses sprout and bud growth, absorbed by leaves and roots and translocated. Enhances chlorophyll production.

CAS RN

123-33-1

Alternative/old CAS RN

10071-13-3

EC number

204-619-9

CIPAC number

310

US EPA chemical code

051501

PubChem CID

21954

Molecular mass

112.1

PIN (Preferred Identification Name)

IUPAC name

6-hydroxy-2H-pyridazin-3-one

CAS name

1,2-dihydro-3,6-pyridazinedione

Other status information

Chemical subject to PIC regulations

Relevant Environmental Water Quality Standards

Herbicide Resistance Class (HRAC MoA class)

Not known

Herbicide Resistance Class (WSSA MoA class)

Not known

Insecticide Resistance Class (IRAC MoA class)

Not applicable

Fungicide Resistance Class (FRAC MOA class)

Not applicable

Examples of recorded resistance

Physical state

White crystalline solid

Related substances & organisms

maleic hydrazide choline

maleic hydrazide potassium

maleic hydrazide sodium

Formulations

Property

Value

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

Bayer CropScience
Dow AgroSciences
Nufarm UK
Vitax Ltd

Example products using this active

Fazor
Source II
Retard
Sprout Stop
Sucker Stuff
Itcan SL 270

Formulation and application details

Usually supplied in liquid formulations

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

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

156000

High

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

4200

Methanol

Toluene

Hexane

35.9

Ethyl acetate

Melting point (°C)

298

Boiling point (°C)

Decomposes before boiling

Degradation point (°C)

310

Flashpoint (°C)

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

1.48 X 10^-02

Calculated

Log P

-1.83

Low

Fat solubility of residues

Solubility

Insoluble

Data type

Regulatory data based metabolism and feeding studies. The magnitude of residues were higher in fat free muscle compared to fat.

Density (g ml⁻¹)

1.61

Dissociation constant pKa) at 25 °C

5.64

Weak acid

Vapour pressure at 20 °C (mPa)

3.1 X 10^-03

Low volatility

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

4.05 X 10^-08

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: 326nm = 2444, and 217nm = 16816
Acidic solution: 306nm = 2376 and 223nm = 8052
Basic solution: 328nm = 2462 and 217nm = 16241

Surface tension (mN m⁻¹)

56.5

at 21 °C 99.9%

Degradation

Property

Value

Source; quality score; and other information

Interpretation

General biodegradability

Soil degradation (days) (aerobic)

DT₅₀ (typical)

0.8

Non-persistent

DT₅₀ (lab at 20 °C)

0.8

Non-persistent

DT₅₀ (field)

Non-persistent

DT₉₀ (lab at 20 °C)

5.5

Non-persistent

DT₉₀ (field)

10.4

DT₅₀ modelling endpoint

Note

EU 2016 dossier field studies DT₅₀ range 0.3-2.3 days, DT₉₀ range 1.4-12.9, Soils=7 days; Other sources: DT₅₀ 30 days anaerobic (DW4)

Dissipation rate RL₅₀ (days) on plant matrix

Value

Note

Dissipation rate RL₅₀ (days) on and in plant matrix

Value

Note

Aqueous photolysis DT₅₀ (days) at pH 7

Value

Stable

Note

pH sensitive: stable pH 5 to pH 7, DT₅₀ ~34 days at pH 9

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

Value

Stable

Note

Stable pH 3 to pH 9

Water-sediment DT₅₀ (days)

186

Slow

Water phase only DT₅₀ (days)

106

Stable

Sediment phase only DT₅₀ (days)

Slow

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)

0.725

Mobile

K_oc (mL g⁻¹)

45.8

Notes and range

EU 2016 dossier K_d range 0.2-1.7 mL g⁻¹, K_oc range 14.5-124.3 mL g⁻¹; Other sources: 250 mL g⁻¹ (DW3)

Freundlich

K_f (mL g⁻¹)

0.48

Mobile

K_foc (mL g⁻¹)

28.16

¹/_n

0.912

Notes and range

EU 2016 dossier K_f range 0.16-1.51 mL g⁻¹, K_foc range 14.4-108.0, ¹/_n range 0.860-0.987, Soils=4

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

1.22

Calculated

Low leachability

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

Value

2.69 X 10^-03

Calculated

Note

Potential for particle bound transport index

Low

Calculated

Potential for loss via drain flow

Mobile

Calculated

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

Bio-concentration factor

BCF (l kg⁻¹)

Low risk

Based on LogP < 3

Low risk

CT₅₀ (days)

No data

Known soil metabolites

Metabolite

Major/Minor fraction

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

Estimated maximum occurrence fraction

Notes

maleic acid

Minor fraction

0.05

Known groundwater metabolites

None

Other known metabolites

None

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 2000

Rat

Low

Mammals - Short term dietary NOEL

(mg kg⁻¹)

> 25

Dog

High

(ppm diet)

> 750

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

> 1216

Rat Reproductive NOAEL

Low

Birds - Acute LD₅₀ (mg kg⁻¹)

4640

Anas platyrhynchos

Low

Birds - Short term dietary (LC₅₀/LD₅₀)

> 10000 mg kg feed⁻¹

Colinus virginianus

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

542.5

Colinus virginianus LD₅₀/10 NOEC

Low

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

> 1000

Low

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

151.5

Eisenia foetida

Low

Soil micro-organisms

Nitrogen mineralisation: No significant adverse effect
Carbon mineralisation: No significant adverse effect

Dose: 5 kg ha⁻¹

Collembola

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

112.7

Folsomia candida 14 day

Non-target plants

Honeybees (Apis spp.)

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

> 100

Apis mellifera

Low

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

> 100

Apis mellifera

Low

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

Chronic NOEC oral chronic µg bee⁻¹ day⁻¹

5.09

Apis mellifera

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)

0% Mortality at dose 3 kg ha⁻¹

Chrysoperla carnea

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

< 3000

Aphidius rhopalosiphi

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

< 3000

Typhlodromus pyri

Beneficial insects (Ground beetles)

Aquatic ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

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

> 1000

Oncorhynchus mykiss as potassium salt

Low

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

9.6

Pimephales promelas as potassium salt 32 day

Moderate

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

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

107.7

Daphnia magna

Low

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

0.95

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)

> 110

Lemna gibba

Low

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

7.45

Myriophyllum aquaticum

Moderate

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

> 100

Chlorella vulgaris

Low

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

Unknown species

Low

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)

> 2000

Rat

Low

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

2000

Rabbit

Mammals - Inhalation LC₅₀ (mg l⁻¹)

> 3.2

Rat (nose only)

Other Mammal toxicity endpoints

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

0.25

Rat SF=100

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

None allocated

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

None allocated

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

0.25

Dog 1 year SF=100

Dermal penetration studies (%)

0.6-1.0

concentration dependent

Dangerous Substances Directive 76/464

Exposure Routes

Public

No unacceptable risks to bystanders identified

Occupational

No unacceptable risks to operators or other workers identified with PPE/PPC

MRLs

European

EU MRL pesticide database

Great Britain

GB MRL Register

Notes

Drinking Water Standards

Drinking Water MAC (μg l⁻¹)

Mammalian dose elimination route and rate

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

; ; ; ;

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

Possiblr

Respiratory tract irritant

Skin irritant

Skin sensitiser

Eye irritant

Phototoxicant

General human health issues

Potential liver toxicant
Possible mutagen; Suspected of causing genetic defects
Ingestion might cause tremors and muscle spasms
IARC Group 3 carcinogen - not classifiable

Handling issues

Property

Value and interpretation

General

Not explosive or oxidising
Not expected to auto-ignite; Not highly flammable

CLP classification 2013

Health: H315, H319, H341, H335

WHO Classification

U (Unlikely to present an acute hazard)

UN Number

Not regulated

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

Chemically stable under standard ambient conditions

TRANSLATIONS

Language

Name

English

maleic hydrazide

French

hydrazide maleique

German

Maleinhydrazid

Danish

maleinhydrazid

Italian

idrazide maleica

Spanish

hidrazida maleica

Greek

Polish

hydrazyd maleinowy

Swedish

maleinhydrazid

Hungarian

maleic hydrazide

Dutch

maleine hydrazide

Norwegian

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