Chapter 4 Fungicides - PowerPoint PPT Presentation

Loading...

PPT – Chapter 4 Fungicides PowerPoint presentation | free to download - id: 7f7b59-MGRhZ



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Chapter 4 Fungicides

Description:

... Protection 1 Definition and Class of Pesticide 2 Toxic Power of Pesticide 3 Effects of Pesticide on Crop 4 Toxicity ... 3 The mercury fungicides ... tomato plants ... – PowerPoint PPT presentation

Number of Views:586
Avg rating:3.0/5.0
Slides: 222
Provided by: anda158
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Chapter 4 Fungicides


1
Plant Chemical Protection
Department of Plant Protection School of
Agriculture,Yangtze University
2
Preface
  • Plant provide either directly or indirectly
    the main source of nutrition for mankind, animals
    and uncountable masses of lower organisms. An
    ample supply of food, fibers and other vegetable
    matter is a prerequisite to health as well as to
    social and economic development of any human
    society. Thus, the increase competition from all
    kinds of organisms, which cause injury, disease ,
    is unwanted. Man is waging a continuous struggle
    against these injurious and troublesome
    organisms, called pest, pathogen and weed etal.
    in order to protect his food, shelter and living.

3
  • Owing to the spectacular development of
    agriculture in general during the 20th century,
    word food production has grown considerable to
    the extent that per capital food production has
    increased in spit of the explosive growth of the
    world population. However, growth figures differ
    greatly for continents and individual countries.
    Developing country provide only about 30 of the
    world requirement of food although they are home
    to more than half of the global population, and
    agriculture accounts for more than 70 of their
    national income in 1985, the ratios for
    malnourished and healthy people were 13 in
    Africa, 15 in east Asia and 17 in Latin
    American.

4
  • In this book, the role of pesticide in
    agricultural productivity has been strongly
    emphasized to sustain the crop yield and quality
    over the world. However, the crop protection is
    very complicated because of the numerous
    interactions between the cultivated crops, the
    many damaging or beneficial organisms and the
    variable factors of the environment. The use of
    chemicals, having an enormously disruptive power
    on the fragile balance of nature, requires
    general insight into their properties and effects.

5
Chapter 1 Basic Concept of Plant Chemical
Protection
  • 1 Definition and Class of Pesticide
  • 2 Toxic Power of Pesticide
  • 3 Effects of Pesticide on Crop
  • 4 Toxicity of Pesticide
  • 5 Principles for Safety Application of
  • Pesticide

6

Section 1 Definition and Classification of
Pesticide
  • Ddefinition of pesticides
  • Classification of Pesticide
  • Classified According to source of Material and
    Component
  • Classified According to Use
  • Classified According to Functional Manner
  • Insecticides
  • Fungicides
  • Herbicides

7
? Definition of Pesticide
  • Any substances or mixture of substances
    and their preparations which were synthesized
    chemically or derived from organisms or other
    natural matters (1) intended for preventing,
    destroying, repelling, or mitigating any pest (2)
    intended for use as a plant regulator, defoliant
    or desiccant.
  • U.S.A.Agricultural Chemicals
  • EuropeAgrochemicals

8
? Classification
  • ? According to Source of Material and Component
  • Inorganic PesticideSulphur,Aluminium
    phosphide, Bordeaux mixture.
  • Organic Pesticide
  • Botanical Pesticide
  • Oil Insecticide
  • Microbial Pesticide
  • Synthetic-organic Pesticide .

9
? Classified According to Use
  • Insecticide
  • Fungicide
  • Herbicide
  • Acaricide
  • Raticide
  • Nematocide
  • Plant Growth Regulator
  • (Hormone mimics).

10
? Classification of Insecticides
  • 1. Stomach poisons
  • 2. Direct contact poison
  • 3. Fumigant
  • 4. Inner absorbent
  • 5. Antifeedant
  • 6. Repellentant
  • 7. Attractant.

11
? Classification of Fungicides
  • 1. Protective fungicides
  • 2. Therapeutic fungicides
  • 3. Eradicant fungicides.

12
? Classification of Herbicides
  • 1. Conducting herbicides
  • 2. Contacting herbicides
  • 3. Selecting herbicides
  • 4. Extinguishing herbicides.

13
Section 2 Toxic Power of Pesticide
  • Concept of toxic power of pesticide
  • Measurement of toxic power
  • Calculation of pesticide effects
  • Insecticide
  • Fungicide
  • Herbicide

14
Concept of Toxicity and Control Effects of
Pesticide
  • Toxic powerA measurement used as evaluated and
    compared index, which was generally determined
    under strict condition with insect, bacteria or
    weed by precision method.
  • Control effectsResulted from pesticides and
    multi factors ,which was determined under field
    condition.
  • ToxicityGenerally refer to mammal and human
    being.

15
Measurement of toxic power of pesticides
  • 1.Unit shows toxic power
  • (1)Lethal Dose LD50
  • (2)Lethal Concentration LC50
  • (3)Effective DoseED50
  • (4)Effective Concentration EC50
  • (5)Knock-down Time KT50
  • (6)Inhibition Concentration, IC50
  • 2.Relative Toxicity Index

16
Calculation of Effects of Insecticides
  • Calculation of adjusted mortality
  • WhereX express percent survival in the untreated
    controlsY express percent survival in the
    treated insect.
  • The approximation is permissible when the control
    mortality is less than 20 or is based on a large
    number or observation.

17
Calculation of Control Effects of Insecticides
Where Ta express the survival individual
before treated in the treated controls Tb
express the survival individual after treated in
the treated controls Ca express the survival
individual after treated in the untreated
controls Cb express the survival individual
before treated in the untreated controls.
18
Calculation of Control Effects of Herbicides
Where Qa express the weed quantity in the
treated controls Qb express the weed quantity in
the untreated controls.
19
Section 3 Effects of Pesticide on Crop
  • ? Damage of pesticide on the crops
  • 1 Property of pesticides
  • 2 Crop species,growth stage and physiological
    status
  • 3 Environmental conditions
  • 4 Symptom of damaged crop
  • A. Acute symptom B. Chronic symptom
  • ? Stimulate effects of pesticide on the growth
    of plant

20
Effects of Properties of Pesticides on Damage on
the Crops
  • Pesticide properties The difference of
    properties of pesticides play important affect on
    the damage effects of pesticide on crop. In
    general, inorganic pesticides have more hazard
    than organic pesticides to bring pesticide
    damage.
  • Where K means safety index Ca express
    the minimum concentration needed to prevent pest
    damage Cb express the maximum concentration that
    plant can endure.

21
Crop species, growth stage and physiological
status
  • The differences of tissue morphology and
    physiology of crop,such as the thickness of wax
    surface, quantity of covering hair , density and
    situation of closure of stomate,etc.,make varied
    crops have different sensibility to the pesticide
    damages.

22
Environmental conditions
  • The occurrence of pesticide damages not
    only has something to do with pesticide class and
    crop,but also has close connection with
    environmental conditions when pesticides were
    applied,mainly connected with the factor of
    temperature, humidity, dew,etc..

23
Acute Pesticide Damage
  • Acute symptom of pesticide damage
    emerged in a short period,even in hours after
    application of pesticides.

24
Chronic Pesticide Damage
  • Symptom of Chronic pesticide damages
    emerged slowly,it need a long time period or
    multiple application of pesticides.

25
Stimulating Effects of Pesticide on Growth of
Crops
  • Tobacco formulation can improve the growth
    of paddyderris formulation can promote the
    development of vegetable roots
  • In general, pesticides when sprayed in low
    dose would stimulate the growth of plant.But this
    positive effects should be affirmed with rigorous
    comparatively research.

26
Section 4 Toxicity of Pesticides
  • Definition of toxicity of pesticides
  • Classification of toxicity of pesticides
  • Acute toxicity
  • Subacute toxicity
  • Chronic toxicity

27
Definition of Pesticide Toxicity
  • ToxicityThe injurious effects of
    pesticide to man and all useful forms of
    life,which were measured by test on rat.Higher
    animals can take in pesticides via
    respiration,oral intake or through dermal contact
    to induce the occurrence of toxicity.

28
Acute Toxicity
  • If man or animal wrongly intake some
    pesticides with high grade toxicity,varied toxic
    symptoms would emerge in a short period,such as
    head faint, nausea, vomit, convulsion or
    decompensation,etc..That would take life risk if
    not cured in time.

29
Subacute Toxicity
  • Subacute toxicity need long time and
    continuate contact with pesticides,the toxic
    symptom emerged over a definite time,but finally
    would have alike symptom of acute
    toxicosis,sometimes would cause local pathology
    symptom.

30
Chronic Toxicity
  • In despite of low toxicity,some pesticides
    with steady property will maintain for a long
    time to pollute environment and food.They will
    accumulate in the body of men and animals after
    long period contact, damaging the function of the
    body and blocking normal physiologic metabolism.

31
Section 5 Primary Principle of Scientific
Pesticide Application
  • Selecting pesticide according to pest
    characteristic
  • Make full use of pesticide properties
  • Take advantage of selectivity of
    pesticide
  • Environmental factors that influence
    control effects
  • Safe application of pesticide.

32
Effects of Properties of Pesticides on Damage on
the Crops
  • Pesticide properties The difference of
    properties of pesticides play important affect on
    the damage effects of pesticide on crop. In
    general, inorganic pesticides have more hazard
    than organic pesticides to bring pesticide
    damage.
  • Where K means safety index Ca express the
    minimum concentration needed to prevent pest
    damage Cb express the maximum concentration that
    plant can endure.

33
Chapter 2 Pesticide Formulation and
Application Method
  • 1 Relationship Between Pesticide
  • 2 Dispersing and Its Application Efficiency
    Adjuvants
  • 3 Main Pesticide Formulation
  • 4 Application Methods of Pesticide

34
Section 1 Relationship Between Pesticide
Dispersing and Its Application Efficiency
  • Difference between technical product
    ,formulation and preparation of pesticide

material
(chemical synthesis)
technical product of pesticide
(pesticide processing)
pesticide preparation
35
  • Concept of dispersing system and dispersing of
    pesticide.
  • ? Dispersing system of pesticidesolid/solid ,
  • liquid/liquid,solid/gas, liquid/gas and
  • gas/gas dispersing system.
  • ? Concept of dispersing of pesticide the
  • dispersed grade of pesticide .

36
  • Effect of enhancing pesticide dispersing on
    efficiency.
  • Increase covering area.
  • Enhance the quality of adherence of pesticide
    granule on processed surface.
  • Change move quality of granule.
  • Enhance surface tension.
  • Enhance suspension and stabilization capability.

37
Section 2 Adjuvants
  • Class of adjuvants
  • Fillers,carrierskaolin, bentonite
  • Wetting agentsBX, detergent powder
  • Emulsifiers
  • Solventsbenzene, toluene
  • Dispersing agents surface-active agents
  • Stickers glutin
  • Stabilizers
  • Synergists SV1.

38
Structure and Effect of Surface-active agents
Structure of surface-active agents (amphiphilic
compound)
Anionic surface-active agents
Hydrophilic part
Hydrophobic part
Cationic surface-active agents
Hydrophilic part
Hydrophobic part

39
  • Hydrophile-Lipophile Balance(HLB)A
    index to express the Hydrophile-Lipophile quality
    of surface-active agents,the higher of the HLB
    values,the more hydrophile of the SAA on the
    contrary, the lower of the HLB values ,the more
    lipophile of the SAA.

40
Surface-active phenomena
41
Effect Reduce surface tension
Air
Interface

Liquid
42
Make spray drop more fine
43
Application in the processing of pesticide
  • As emulsifiers used in emulsifiable concentrates.

Oil
water
water
Oil
Oil
44
  • As wetting agents used in wet table powders .
  • Enhance the adherence ability of pesticide on
    sprayed surface.

45
Class of surface-active agents
Anionic SAA Cationic SAAOrganic
amine Amphiphilic SAAester and aether Nonionic
SAA Natural SAA
46
Anionic SAAWidely used, such as sodium
dodecyl-benzene sulphonate, such as calcium
dodecyl-benzene sulphonate.
Sodium dodecyl-benzene sulphonate
47
Section 3 Main Pesticide Formulation
  • Dusts
  • Granules
  • Wet table powders
  • Soluble powders
  • Suspension concentrates and colloidal
    formulations
  • Emulsifiable concentrates
  • Seed coatings
  • Oil solutions
  • Controlled release formulations
  • Smokes

48
? Dusts
  • ConstituteTechnical products and carriers.
  • Standard95 of pesticide can sieve through 0.074
    µm mesh screen.
  • Characteristiceasy to useneed no waterhigh
    efficiency.
  • Shortcoming pollute environmentbad control
    effects.

49
? Granules
ConstituteTechnical products,adjuvants and
carriers. Classificationmacrogranulesgranulesmi
crogranules. Standard90 can match the standard
of particle size moisture contentlt3. Characteris
ticlower toxicity of high grade toxic pesticides
in usecontrolled releaseeasy to use reduce
pollution.
50
? Wettable powders
ConstituteTechnical products,wetting
agents,dispersing agents and carriers. Classificat
ionmacrogranulesgranulesmicro
granules. Standard moisture contentlt3 pH59
wetting time1-2minparticle diameter37 µm
suspension rategt70. Characteristichigh
develop quality.
51
? Soluble powders
ConstituteTechnical products,wetting agentsand
carriers. Standard moisture contentlt3 wetting
time2-3min. Should pay attention to distinguish
the difference with wetting powders.
52
? Suspension concentrates and colloidal
formulations
Suspension concentrates ConstituteTechnical
products and multiadjuvants. Standard particle
diameter0.55 µm suspension rategt90. Colloidal
formulations ConstituteTechnical products and
multiadjuvants. Standard particle
diameter0.010.1 µm should be in colloidal
condition in liquid.
53
? Emulsifiable concentrates
ConstituteTechnical products,solvent, emulfiers
and cosolvent. Classificationstock emulsions,
aqueous solutions, emulsifiable
concentrates. Characteristichigh control
effects. Shortcoming consume a great deal of
organic solvent,pollute environment, have trouble
in transportation.
54
Emulsifiable concentrates processing
vacuum
vacuum
sampling
Chart of emulsifiable concentrates
processing 1.technical produsts 2.mearsure of
quantity of technical produsts 3.solvents 4.
mearsure of quantity of solvents 5.modulating
kettle 6.condensation device7. filtration
device 8.container of emulsifiable
concentrates9.products packaging
55
? Seed Coatings
  • Formulations of seed covered with pesticides.
    Covering pesticides were derived from SC,WP or EC
    mixed with stickers to form firm pesticide layer.
  • Attentionseed coatings is different with seed
    treat concentrates.

56
? Oil Solutions
Oil solution of technical products,should be
added in solvents and stabilizers in the
processing.It was also named ultra low volume
agents. Characteristicgenerally contain 2050
of effective component,can be used with no more
dilution. Should pay attention to distinguish the
difference of EC,SE,AS and OS.
57
? Controlled Release Formulations
  • Pesticide formulation in which the effective
    component of pesticides can be controlled to
    release slowly.
  • Physical controlled release formulations
    microcapsule formulations, plastic formulations,
    poly-stripe formulations,fibrous sheet
    formulations and porous material formulations.
  • Chemical controlled release formulationsintegrate
    with chemical reaction.

58
? Function of Controlled Release Formulations
  • Lower toxicity of high grade toxic pesticides in
    use.
  • Prolong effective period of pesticides.
  • Decrease applied quantity of pesticides.

59
? Smokes
Pesticide formulation when ignited,the effective
component of pesticides suspending in dispersing
state like smoke in air. ConstituteTechnical
products, fuel(varied carbohydrate),oxidant and
extinguish agents.
60
Section 4 Pesticide Application Methods
  • Spraying
  • Dusting
  • Other application methods
  • Application on mixed pesticides and Synergist
  • Calculation of co-toxicity coefficient
  • Synergist

61
? Spraying ?
  • Effects of equipment on dispersing of pesticides
  • Pressurized spraying
  • Atomizing spraying
  • Ultra low volume atomizing spraying.
  • Effects of physical and chemical property of
    pesticides on deposit quantity.
  • Relationship of deposit quantity and surface
    structure of creature.
  • Effects of quality of water on capability of
    pesticides.

62
? Dusting ?
  • A method utilizing airflow produced by fan to
    bring pesticides dust deposited on surface of
    crop.
  • Effects of equipment and operation on uniform
    distribution of pesticides.
  • Effects of environmental conditions on dusting
    quality.
  • Effects of physical property of dusts on dusting
    quality.

63
? Other Application Methods ?
  • Spread and slosh irrigating
  • Soil spraying
  • Seed milling
  • Seed immersing
  • Poison lure
  • Fumigating.

64
Application on mixed pesticides and Synergist
Calculation of co-toxicity coefficient
65
Class of synergist and synergistic effects
Pb
Sesamin

66
Application via plane
  • Advantages and disadvantages of application by
    plane
  • Equipment of dusting and spraying
  • Manner of spraying
  • Placement spraying
  • Incremental drift spraying.

67
Chapter 3 Insecticides
  • 1 Botanical insecticides
  • 2 Synthetic insecticides
  • miscellaneous and organ chlorine compounds
  • organ phosphorus and carbamate compounds

68
Section 1 botanical insecticides
  • Plants have evolved over some 400 million
    years and to combat insect attack they have
    developed a number of mechanisms, such as
    repellency, and insecticidal action. Some of
    these have been used by man as insecticides since
    very early times although many of them cannot
    profitably be extracted. However, several of
    these extracts have provided valuable contact
    insecticides which possess the adventage that
    their use does not appear to result in the
    emergence of resistant insect strains to the same
    degree as the application of synthetic
    insecticides.

69
  • Some botanical insecticides survive today
    the most important example, in ascending order of
    importance, are nicotine derris (rotenone), and
    pyrethrum.
  • Nicotine
  • The tobacco plant was introduced into Europe
    about 1560, Sir Walter Raleigh began the practice
    of smoking tobacco in England in 1585, and as
    early as 1690 water extracts of tobacco leaves
    were begin used to kill sucking insect on garden
    plants. The active principle in tobacco extracts
    was later shown to be the alkaloid nicotine(1),
    first isolated in 1828 and the structure
    elucidated.

70
Nicotine functions as a non-persistent
contact insecticides against aphids, capsids,
leaf miner, codling moth, and thrips on a wide
variety of crop. However, its use is rapidly
declining and it is been replaced by synthetic
insecticides, because of its lack of
effectiveness in cold weather. The compound is
readily absorbed by the skin and any splashes
must be washed off immediately.
(1)
71
  • Rotenoids
  • These are a group of insecticidal compounds
    occurring in the roots of Derris elliptical from
    a species of Lonchocarpus. Derris has been used
    as an insecticide for a long time, thus Oxley
    recommended it for control of caterpillars.
    Derris dust is manufactured by grinding up the
    roots and mixing the powered from the powdered
    roots with organic solvents. Its molecule
    structure is

72
  • ROTENOIDS

73
  • Pyrethroids
  • Pyrethrum is a contact insecticide obtained
    from the flower heads of Chrysanthemum
    cinerariaefolium and has been used as an
    insecticide since ancient times. The varieties
    grown in the highlands of Kenya yield the highest
    proportions of active ingredients it is also
    grown commercially in the Caucasus, Iran, Japan,
    Ecuador and New Guinea.

74
Gem-dimethyl group acid
alcohol
Compounds R R
Pyrethrin -CH2CH2 -CH3
Pyrethrin 2 -CH2CH2 -CO2CH3
Cinerin 1 -CH3 -CH3
Cinerin 2 -CH3 -CO2CH3
75
Section 2 Synthetic insecticides
  • ? Miscellaneous and organochlorine compounds
  • In recent years synthetic insecticides have
    been gaining at the expense of naturally
    occurring insecticidal products, apart from
    pyrethroids whose production has continued to
    rise in spite of the growth of synthetic
    compound.

76
  • Miscellaneous
  • The earliest synthetic contact insecticides
    were inorganic materials the pigment Paris
    Green, a copper aceto-arsenite of approximate
    composition
  • Cu4(CH3COO)2(AsO2)2 was successfully employed in
    the united state of America for the control of
    colorado beetle on potatoes. Lead arsenate ,
    PbHAsO4 , was used in 1892 against the gipsy moth
    in forests in the eastern united state.

77
  • Organic thiocyanates
  • In a series of alkyl thiocyanates obtained
    by reaction of alkyl halides with sodium
  • thiocyanate, the insectical activity increased
    with the length of the alkyl chain up to the
    dodecyl derivative and then declined. The dodecyl
    compound was the most active because it possessed
    the optimum oil/water solubility balance for
    penetration of the insect cuticle. A more useful
    compound was, however, 2-(2-butoxyethoxy) ethyl
    thiocyanate or lethane
  • (4 R-CH2CH2OCH2OC4H9) discovered in 1936.

78
Organochlorine insecticides
  • The most important member of this group of
    insecticides is 1,1,1-trichloro-2-2-di-(p-chloroph
    enyl)ethane also termed dichlorodiphenyltrichloroe
    thane or DDT. This compounds was first prepared
    by Zeidle(1874) but its powerful insecticidal
    properties were not discovered until 1939 by
    Muller of the Swiss Geigy company.

79
  • DDT is manufactured by condensation of chloral
    chlorobenzene in the presence of an excess of
    concentrated sulphuric acid

80
The cyclodiene group
  • The insecticidal properties of chlordance
    were reported in 1945-this was the first member
    of a remarkable new group of organochlorine
    insecticides. These compounds are prepared from
    hexachlorocyclopentadiene by the Diels-Alder
    reaction for instance with cyclopentadiene the
    product is chlorine. This is only slightly toxic
    to insect but subsequent addition of chlorine
    gave the highly active compounds chlordance and
    heptachlor

81
(No Transcript)
82
  • ? Organophosphorus and organocarbamate compounds
  • The organic chemistry of phosphorus goes back to
    1820 when Lassaigne first studied of alcohol with
    phosphoric acid. In 1854 Clermont prepared
    tetraethyl phosphorate by heating the silver salt
    of phosphoric acid with ethyl choride although
    the powerful insecticidal properties of this
    compound were not discovered until some years
    later.
  • Organophosphorus

83
  • Serious investigation into the synthesis of
    toxic organophosphorus compounds as potential
    nerve gases began during the second World War. At
    Cambridge Saunders and his colleagues studied
    alkyl fluorophosphate such as tetramethylphosphoro
    diamidic fluoride or dimmefox, while in Germany
    Schrader made the hignly active nerve gases tabun
    and sarin.

84
  • All these compounds are powerful
    insecticides, but on account of their extremely
    high mammalian toxicities, they have never been
    extensively used as insecticides. However dimefox
    is still permitted as a systemic insecticide for
    the control of aphids and red spider mites on
    hops by soil application.

85
  • Schradan can be manufactured by a one-stage
    process from phosphorus oxychloride and
    dimethylamine without isolating the intermediate
    chloridate. Historically Schradan was the first
    organophosphorus compound recognized to be a
    potent systemic insecticide, though dimefox is
    also systemically active. However schradan has a
    high mammalian toxicity LD50(oral) to rats is
    about 8 mg/kg, and it has been replaced by the
    less systox series.

86
  • Others is also high mammalian toxicity
    insecticide such as

87
Mode of action of organophorus insecticides
  • The insecticidal organophosphorus compounds
    apparently inhibit the action of several enzymes,
    but the major action in vivo is against the
    enzyme acetylcholinesterase. This control the
    hydrolysis of the acetylcholine, generated at
    nerve junctions, into choline. In the absence of
    effective acetylcholinesterase, the liberated
    acetylcholine accumulates and prevents the smooth
    transmission of muscular coordination,
    convulsions, and ultimately death.

88
  • Acetylcholinesterase is an essential component
    of the nervous systems of both insects and
    mammals so the basic mechanism of toxic action of
    the organophosphorus compounds is considered to
    be essentially the same in insects and mammals.
    The active centre of the enzyme
    acetylcholinesterase contains two main reactive
    sites an anionic site which is negatively
    charged and binds onto the cationic part of the
    substrate, and the esteratic site containing
    the primary alcoholic group of the amiino acid
    serine which attacks the electrophilic carbonyl
    carbon atom of the substrate. The normal enzymic
    hydrolysis of acetylcholine to choline may
    therefore be illustrated as shown Fig. A

89
Fig A
90
  • Fig A depicts the formation of the initial
    enzyme-substrate complex by the orientation of
    the active centers of acetylcholinesterse to the
    substrate. Fig A shows formation of the
    acetylated enzyme, which is subsequently rapidly
    hydrolysed to choline and acetic acid leaving the
    enzyme with both its actives sits intact, so
    permitting it to repeat the enzymic hydrolytic
    process on further substrate molecules releasing
    several thousand choline molecules per second.

91
Organophosphorus
  • The successful development of organophorus
    insecticides stimulated examination of other
    compounds known to possess anticholinesterase
    activity. One such compound is the alkaloid
    physostigmine, the active ingredient in calaban
    beans which has been used for trial by ordeal in
    West Africa. The physiological properties of this
    alkaloid were supposed to be based on the
    phenylmethyl-carbamate part of the structure and
    led to the discovery of a number of
    parasympathomimetic drugs like neostigmine.

92
  • The compounds being quit strong bases are
    ionized in aqueous solution and therefore have
    very low lipid solubility. Consequently they are
    unable to penetrate the ion-impermeable sheath
    surrounding the insect nervous system. Therefore,
    efforts were made to synthesize compounds in
    which the N-substituted carbamate part of the
    molecule was attached to a less basic, more
    lipophilic moiety, since such compounds should
    show greater insecticidal activity. In 1951 the
    Geigy company introduce Isolan(1-isopropyl-3-methy
    lpyrazolyl-5-dimethylcarbamate).

93
(No Transcript)
94
Resistance of insects towards insecticides
  • Resistance may be defined as the ability of a
    given strain of insects to tolerate doses of an
    insecticide which would kill the majority of a
    normal population of the same insect species.
    Some of the best documented cases of insect
    resistance have been observed with DDT and other
    persistent organochlorine insecticides, though
    serious resistance to organophosphorus and other
    insecticides has also been noted and has caused
    serious control problem.

95
  • By 1946 some strained of DDT-resitant
    houseflies had been discovered and in 1950,5 to
    11 species had acquired tolerance to one or more
    insecticides. In 1969 there were 102 resistant
    insect species 55 to DDT, 84 to dieldrin, and 17
    to organophosphorus compounds. Further some
    insects were resistant to all three type of
    insecticide. In addition 20 species of mites and
    ticks had developed tolerance to acaricides. By
    1974, it has been estimated that over 250 species
    had become resistant to one or more insects. One
    of the early example of an insect acquiring
    tolerance to an insecticide was recorded in
    California in the 1920s when scale insects
    infesting citrus orchards become resistant to
    hydrogen cyanide.

96
  • It was however not expected that the
    introduction of the new synthetic insecticides in
    the later 1940s would induce such rapid insect
    resistance. The reason was probably that these
    chemicals had extremely high initial toxicity and
    so they quickly killed all the susceptible
    individuals in the pest population leaving the
    small number of naturally resistance pests
    available to reproduce explosively with little
    competition because these non-selective
    insecticides often eliminated many of the natural
    predators.

97
  • Pesticides do not produce resistance, they
    merely select resistant individuals already
    present in the natural pest population. The
    tolerant individuals confer resistance to their
    progeny in the genes so succeeding generations of
    insects will also be resistant to the pesticides.
    In the majority of cases, the pesticide probably
    does not induce mutations which confer
    resistance, though this may be true for
    warfarin-resistant rats which have appeared in
    Central Wales.

98
  • In screening a new potential insecticides, it
    is therefore important to see whether it is
    effective against strains of the target pest
    which are already tolerant to established
    insecticides, and also how quickly a strain
    resistant to the new chemical develops.

99
  • The addition of synergists is also often
    helpful in overcoming resistance for instance,
    DDT-dehydrochlorinase inhibitors such as WARF
    antiresistant

100
  • Have restored the toxicity of DDT to
    populations of resistant houseflies. Piperonyl
    butoxide inhibits microsomal enzymes and has been
    useful against insects that have developed
    tolerance to some organophosphorus and carbamate
    insecticides while with malathion-resistant
    insects, the most effective synergists were
    triphenyl phosphate, tributyl phosphorotrithioate(
    DEF) and several dimethoate-resistant insects can
    be inhibited by methylene dioxyphenyl synergists
    themselves which can substantially reduce the
    effectiveness of synergist-insecticide mixture.

101
Chapter 4 Fungicides
  • 1 The story of fungicides
  • 2 The nature of fungicides
  • 3 The Inorganic fungicides
  • 4 The Organic fungicides

102
Section 1 the story of fungicides
  • The story of the use of chemicals for disease
    protection of crop plants upon which man has
    always depended for food, for clothing and for
    shelter, is as old as the sands of time. While
    the citizens of the jet age, it is but prudent
    to reflect that such progress as we now enjoy was
    nurtured in the womb of countless eons of time,
    and was neither born today nor in any century.

103
  • Plant protection by the use of chemical
    sprays, dusts, of seed treatment, did not
    originate in the 20th century but has been
    practised in some form for as long as man has
    record the story of his trials, troubles and
    tribulations.
  • ? Ancient fungicides
  • Early agriculturalists were aware of the
    seriousness of losses caused by plant diseases.
    While their knowledge of these maladies was
    clouded by superstitious beliefs and erroneous
    concepts they nevertheless did attempt to prevent
    losses to their crops caused by blight and
    mildew. Most of the early attempt were made to
    utilize chemicals as fungicides.

104
  • ? Fungicides in the 18th century
  • Students of phytopathology who have browsed
    in the archives that contain the early knowledge
    of plant diseases are aware that science and
    learning slumbered from the fall of the Roman
    empire in 476 A.D., until the start of the
    Rennaisance in the 13th century. Throughout these
    centuries nothing was added to our knowledge of
    plant diseases and no attempts were made to
    prevent the crop losses which they caused. During
    all these centuries man seemed to be more
    concerned with saving his soul than in saving his
    crops.

105
  • ? Fungicides in the 19th century
  • By the beginning of the 19th century the
    activities of the Linnaean taxonomist had
    stimulated interest in abnormalities of plants
    and certain workers began attempts to classify
    fungi even through their role as inciters of
    plant diseases was not yet established. Even
    before science drew aside the veil of mystery
    shrouding the true cause of plant diseases,
    chemicals were used as fungicides even through
    their mode of action in preventing plant diseases
    was understood not at all. Thus, Remnant in 1637
    mentioned the value of seed treatment of wheat
    with sodium chloride for the prevention of bunt
    or stinking smut. The English farmers of the
    1600s regularly practiced dipping seed wheat
    from Australia in ocean water for bunt control.
    This is the first example of seed protection with
    chemicals.

106
  • ? Fungicides in the 20th century(1900-1930)
  • At the start of the 20th century. Bordeaux
    mixture and lime-sulfur reigned as undisputed
    kings of the fungicides word. Both of these
    fungicides were universally used for the control
    of all plant diseases. It as soon discovered that
    while these mixture had their virtues, they also
    had their faults. Both Bordeaux mixture and
    lime-sulfur were excellent fungicides but neither
    was pleasant to used were injurious to foliage
    and fruit under some conditions. Agriculturalists
    in the USA began to demand safe fungicides for
    plant disease control. The introduction of
    self-boiled lime-sulfur by Scott in 1908 offered
    temporarily a safer fungicide for fruit disease
    control. Scotts self-boiled lime-sulfur was made
    by slaking together 15 pounds of quicklime and 10
    pounds of finely divided sulfur

107
  • in a small amount of water with constant stirring
    and then quenching the batch with more water as
    soon as yellow streaks of polysulfide began to
    show. The entire batch was further diluted with
    water to make 50 gallons of spray. Needless to
    say, several years by peach growers in the USA as
    a less caustic fungicides than liquid
    lime-sulfur.
  • ? modern Fungicides (1930-)
  • In 1931, the U.S.D.A.,established a project
    to search for non-corrosive substitutes for
    standard fungicides under the direction of
    J.W.Roberts with M.C.Goldsworthy and E.L.Green.
    As a result of this project a better under
    understanding was arrived at concerning the
    fundamental characteristics of the low-soluble
    copper compounds.

108
  • Methods for copper analysis were developed
    which made possible the determination of very
    small quantities of copper. Biological assay
    methods were also developed for distinguishing
    between soluble copper and available copper thus
    enabling the research works to determine more
    precisely the fungicidal capabilities of the
    fixed copper fungicides. The pioneering work of
    this federal project led to the adaptation by US.
    Agriculture of the low-soluble coppers as
    bordeaux substitutes. While J.W.Roberts and
    M.C.Goldsworthy were engaged in search designed
    to develop bordeaux substitutes as fruit
    fungicides other works were trying to find
    similar substitutes for vegetables.

109
  • There is no reason why superior materials
    cannot be developed be cause knowledge is rapidly
    becoming available to guide the research effort
    away from blind probing and wild conjectures
    which had to prevail in the early days. The
    foundations have been laid for the young science
    of fungous toxicology which should grow and
    flourish in the next century more than it has in
    the past.

110
  • Section 2 the nature of fungicides
  • The word fungicide is derived from the Latin
    words caedo to kill, fungus a fungus. Hence
    in its literal sense a fungicides is any agency
    that has the ability to kill a fungus. Heat,
    acids, ultraviolet light and other physical
    agents are thus fungicides. However, by common
    usage the term fungicides is usually confined
    to chemicals capable of preventing infection of
    living plants by phytopathogenic fungi. The term
    is also used describe chemicals.

111
  • Such cases the chemical is said to be a
    fungistat, or to possess fungistatic
    properties. Other chemicals such as bordeaux
    mixture and certain phenanthrene derivatives, may
    inhibit or prevent spore production without
    affecting vegetative growth of fungus hyphae.
    Fungicides of this type have been referred to as
    a genestatic substance or an anti-sporulant.
    Although the term fungicide is more correctly
    used when referring to chemicals which kill
    fungi, public interest in their use has
    corrupted the term to apply to chemical compounds
    capable of preventing damage to growing crops
    caused by fungi.

112
  • Section 3 The Inorganic fungicides
  • 1 The sulfur fungicides
  • Sulfur has been known science remote
    antiquity the Greek called it theion, the first
    called it sulfur.
  • Elemental sulfur in the finely divided
    condition is not wettable and must be treated
    with suitable conditioning agents before it can
    be used as a fungicidal spray. For example,
    flotation sulfurs, grinrod process sulfurs,
    micron zed sulfurs, conventionally milled
    sulfurs, bentonite sulfurs, etc.

113
2 the copper fungicides
  • Copper sulfate at one time reigned as
    undisputed king of the blight busters . The
    use of copper sulfate in agriculture appears to
    be yielding more and more to the synthetic
    organic fungicides such as captan, ferbam, zineb,
    maneb, etc. nevertheless,copper fungicides are
    still used in significant quantities for plant
    disease control.

114
  • ?The Bordeaux mixture is the most important
    fungicides in the copper fungicides.
  • Bordeaux mixture as a combination of matter
    apparently was first prepared by the French
    chemist Proust in 1800. In 1882 Bordeaux mixture,
    prepared by combining hydrated lime and copper
    sulfate in various proportions was accidentally
    discovered by the French workers, Millardet and
    Gayon, to be an effective protectant against
    downy mildew disease of grape.

115
  • Bordeaux formula of various concentrations may
    be prepared by using varying amounts of the stock
    solutions in a given amount of water. Thus a
    formula such as

2-4-50 means 2 lbs, CUSO4 5H2O
2-4-50 means 4 lbs, lime
2-4-50 means 50 gals water
4-4-50 means 4 lbs, CUSO4 5H2O
4-4-50 means 4 lbs, lime
4-4-50 means 50 gals water
1/2-3-100 means 1/2 lbs, CUSO4 5H2O
1/2-3-100 means 3 lbs, lime
1/2-3-100 means 50 gals water
10-10-100 means 10 lbs, CUSO4 5H2O
10-10-100 means 10 lbs, lime
10-10-100 means 50 gals water
116
3 The mercury fungicides
  • The fungicide of mercurial compounds
    have been recognized for many years. they may be
    conveniently grouped into two major divisions,
    viz
  • A. Inorganic mercurials
  • B. Organic mercurials

117
  • The first use of inorganic mercury in any
    form as a fungicides appears to be its
    utilization by Homberg in 1705 as a wood
    preservative. Corrosive sublimate was later used
    by Aucante as a seed treatment for the control of
    stinking smut of wheat in 1775. Mercuric chloride
    had been recognized as a powerful germicide for
    many years and this this undoubtedly led to its
    adoption as a seed disinfectant.

118
  • The phytotoxicity and mammalian toxicity of
    inorganic mercurials was largely responsible for
    efforts to develop other mercury derivative as
    fungicides. The first organic mercury actually
    used as a fungicide was introduced in 1914 by
    Riehm in Germany who suggested that chlorophenol
    mercury was an effective seed disinfectant for
    the control of bunt or stinking smut of wheat.

119
Section 4 The organic fungicides
  • 1 The carbamate fungicides
  • All of the carbamate fungicides at present
    available commercially are derivatives of
    dithiocarbamic acid (NH2.CS2.H). This organic
    acid does not occur in the free state and was
    synthesized in the 1920s to accelerate the
    action of sulful in vulcanizing rubber.

120
This acid represented by the structural formula
121
The fungicidal derivatives of this compound
may be classified into three group
  • (1) thiuram disulfides
  • Foe exampletetramethylthiuram
    disulphide(common nameThiram)
  • (2) metallic dithiocarbamates

122
(3) ethylene bisdithiocarbamates
The metallic dithiocarbamate fungicides are
characterized by the folloeing structure formula
123
  • Thiuram disulfides is formed by joining two
    molecules of dithiocarbamic acid through the S
    atom. Tetramethylthiuram disulfide is at present
    the only member of this chemical family that has
    found usage in the control of plant disease. This
    compound was originally developed as a rubber
    accelerator and was introduced for this purpose
    under the trade name of Tuads.

124
  • The various formulations of Thiram are as follows

Arasan 75 75 tetramethylthiuram disulfide.
Arasan SF-M 75 tetramethylthiuram disulfide Plus 2 methoxychlor.
Arasan 42-S 42 tetramethylthiuram disulfide.
Delsan A-D 60 tetramethylthiuram disulfide Plus 15 Dieldrin.
Tersan 75 75 tetramethylthiuram disulfide.
Tersan DM 45 tetramethylthiuram disulfide Plus 10 hydroxymercurichlorophenol
Thylate 65 tetramethylthiuram disulfide
125
Several kinds of fungicides data
  • Common name nabam
  • Chemical name disodium ethylenebisdithiocarbamate
  • Empirical formula C4H6N2Na2S4
  • Chemical and physical properties
  • molecular weight256.3 melting
    pointdecomposes before melting physical state
    solid color white flammability
    non-comlustible, but may form combustible
    decomposition products
  • solubility relatively unstable to heat, light
    and moisture but solution are stable.
  • toxicityoral to mammals acute LD50
    395mg/kg, chronic 1000-2500ppm in diet of rats
    produced
    goitrogenic effect in 9-10 days
  • FDA tolerance7ppm on fruits and vegetables

126
  • Common name zineb
  • Chemical name zinc ethylenebisdithiocarbamate
  • Empirical formula C4H6N2S4Zn
  • Chemical and physical properties
  • molecular weight275.7 melting
    pointdecomposes physical state powder color
    white to off-white flammability flash point
    280-290?, solubility soluble in pyridine
    solubility in water over 10ppm. toxicityoral to
    mammals acute LD50 50mg/kg, chronic 1000ppm in
    diet of rats for 74 weeks cause growth
    depression.
  • FDA residue tolerance 7ppm on fruits and
    vegetables 60ppm on hops 1ppm on wheat.

127
  • Common name maneb
  • Chemical name manganese ethylenebisdithiocarbamat
    e
  • Empirical formula C4H6MnN2S
  • Chemical and physical propertiesmolecular
    weight265.3. melting pointdecomposes before
    melting. physical state crystalline. color
    yellow. flammability flash point (open cup)
    above 300?, solubility only slightly soluble in
    water possible very slightly in some organic
    solvent. toxicity oral to mammals acute LD50
    7500mg/kg(rats), chronic feeding tests with rats
    indicated low chronic toxicity FDA residue
    tolerance 0-10ppm on fruits and vegetables
    0.1ppm on almonds and potatoes.

128
2 The glyoxalidine fungicides
  • From the beginning of mordern methord of
    chemical controls for plant disease the
    fungicides used as spry for the protection of the
    major fruit crops have been attended by varying
    degrees of injury to the fruit and foliage to
    witch they are applied. The choice of fungicides
    as well as the methods of applying them has
    always involved an attempt to balance
    satisfactory control against minimum injury. In
    1946 Wellman and Mccallan discovered the
    fungicidal properties of the derivatives of
    glyoxalidine which lead to the introduce of
    glyodin, in the common name for fungicides
    derived from glyoxalidine.

129
  • The glyoxalidine Nucleus is a hetero-cyclic ring
    compound more correctly referred to as an
    imidazoline nucleus. Its nucleus is
    represented as

130
Fungicide data sheet-glyodin
  • Common name glyodin
  • Chemical name 2-heptadecyl glyoxalidine acetate
  • Empirical formula C22H44O2N2
  • Chemical and physical properties molecular
    weight 368.6. melting point62-68 ?. physical
    state powder. color light orange. flammability
    solution is flammable. solubility almost
    insoluble in water. toxicity oral to mammals
    acute LD50 5.77mg/kg, chronic 0.15 in diet of
    rats for years reduced growth and produced heavy
    lives.
  • FDA residue tolerance 5ppm on fruits and
    vegetables

131
3 The quinone fungicides
  • Quinones have been known for more than a
    century yet their use as fungicides for plant
    disease control was discovered only as recently
    as 1940. The quinones have a cyclic, its wide
    chemical reactivity of this group is undoubtedly
    important in their fungicidal activity. e.g.
    benzoquinone, naphthoquinone etc.. The molecular
    structure viz.

132
The Application technique of fungicides
  • a. Kittlesons Killer-captan
  • b. Guanidine fungicides-cyprex
  • c. Miscellaneous fungicides
  • d. Antibiotics for plant disease control
  • e. Seed treatment for plant disease control
  • f. Soil treatment for plant disease control

133
Chapter 5 Herbicides
  • 1 Introduction
  • 2 Classification
  • 3 Use of herbicides
  • 4 mechanism of action
  • 5 herbicide and environment

134
Section 1 introduction
  • Weed have been part of the agricultural scene
    since Man first started cultivating crop more
    than 10000 years ago and they are still a major
    problem today. They have been defined as plants
    growth in the wrong place which means that
    every plant species is a potential weed. In other
    words the question of whether a plant is a weed
    or not is a subjective judgement. In addition,
    successful weeds are aggressive, competitive and
    adaptable.

135
  • Weed are harmful to crops in many ways
  • 1. They compete for water
  • 2. They compete for light
  • 3. They compete for nutrients
  • 4. They compete for space above and below
    ground
  • 5. Some weeds , e.g. dodder may be parasitic on
    crop plants
  • 6. They may reduce the value of produce,
    increase
  • the difficulty of harvesting and entail seed
    cleaning
  • 7. Some, e.g. ragwort and water dropwort are
  • poisonous to stock
  • 8. They may harbour pests and disease. etc.

136
Section 2 Classification of herbicides
  • No classification is perfect and the
    classification of herbicides is a particularly
    task. Many options are available on which
    applied, modern of action, chemical structure.
  • ?Inorganic compounds
  • for example
  • Copper sulphate(CuSO4)
  • Sulphuric acid(H2SO4)
  • Sodium chlorate(NaClO3)
  • Sodium tetraborate pentahydrate
    (Na2B4O7.5H2O)
  • Ammonium sulphamate(NH4SO3NH2)

137
  • ?Haloalkanoic acids
  • for example sodium trichloroacetate(CCl3COONa)
  • dalapon(CH3CCl2COOH)
  • Sodium chlorate(NaClO3)
  • Chlorfenprop-methyl
  • ?Phenoxyalkanoic acids
  • ?Phenoxyacetics
  • ?Phenoxybutyrics
  • ?Phenoxypropionics
  • ?Aromatic acids
  • ?Amides
  • ?Nitriles
  • ?Anilides

138
Section 3 Use of herbicides
  • The idea of controlling weeds with chemicals
    is not new, for more than a century chemicals
    have been employed for total weed control, but
    sometimes we need all plants were killed. e.g.
    railway station, timber yard and unmetalled roads
    etc. but more case is kill the weed selectively.
    The first important discovery in the field of
    selective weed control was the introduce of
    2,4-dinitro-o-cresol(1RCH3)(DNOC or Sinox) in
    France in 1933.

139
The absorption and translocation of
foliage-applied herbicide
  • The activity of a foliage-applied translocated
    herbicide depends largely on factors which govern
    of active ingredient reaching the sites of
    action.
  • For example
  • leaf age, surface of application, herbicide
    concentration, Ph, molecular structure,
    additives, environmental factors.

140
Short and long distance transport
  • Subsequent to penetrating the cuticle,
    lipophilic herbicide must partition into the
    apoplast(or cell wall continuum including the
    xylem). Ester formulations which are strongly
    lipophilic are apparently hydrolysed and
    thereafter partition into the aqueous phase. Some
    compounds, such as the substituted ureas and
    triazines when foliage applied are apparently
    unable to penetrate the symplast and move only in
    the apoplast within and not out of the treated
    leaf such compounds are normally root absorbed
    and xylem transported.

141
(No Transcript)
142
Uptake and translocation of soil-applied
herbicides
  • Amides
  • Compounds belonging this group are generally
    taken up readily by the roots and transported to
    the foliage. For instance root absorption of
    diphenamid appears to occur rapidly, most of the
    herbicide accumulating in the leaves. The rate of
    uptake and translocation of 14C-diphenamid has
    been found to vary according to the species
    tested. For example, apoplastic translocation of
    diphenamid was rapid in tomato seedling,
    intermediate in Bermuda grass and slow in winged .

143
  • Euonymus. Light and humidity regimes also
    have an effect on absorption of 14C-diphenamid.
    For example, tomato plants grown under low light,
    low humidity conditions accumulated higher levels
    of diphenamid in the shoots than did those grown
    under high light, high humidity conditions.

144
  • Nitriles
  • In contrast to the hydroxybenzonitriles,
    dichlobenil and chlorthiamid are essentially
    pre-emergence herbicides which are absorbed by
    the roots and transported to a limited degree in
    the xylem in the transpiration stream. However,
    shoot absorption of dichlobenil by beans exposed
    to a saturated atmosphere of the chemical has
    been reported(Massini, 1961).

145
  • Anilides
  • Compounds of the anilide group are generally
    readily absorbed by the roots and transported in
    the xylem to the shoots. For example, propachlor
    is absorbed by the roots of maize and soybean,
    through it may be more readily taken up from the
    soil by the shoot than by the shoots. Foliage
    absorption of certain anilides such as dicryl,
    propanil and solan has also been reported but
    translocation appears to be very limited.

146
  • Nitrophenyl ethers
  • In this group of compounds nitrofen,
    fluorodifen, chlornitrofen and acifluorofen may
    be applied pre- or post-emergence, though on
    balance they are probably more often used a
    soil-applied on emergence herbicides. Which root
    absorption general appears to be rapid, xylem
    transport to the shoot may be restricted and
    differentials in the efficiency of root
    absorption and translocation may occur relatively
    readily in some species, symplastic transport
    appears to be restricted, movement being
    acropetal in nature.

147
  • Nitro anilines
  • The major route of absorption and translocation
    of the nitro aniline herbicides is a matter of
    some controversy but the predominant evidence
    suggests that they are readily absorbed by roots
    and shoots though generally translocation is
    minimal.
  • Absorption of trifluralin has been reported by
    both root and emerging shoots of sorghum
    seedlings or green foxtail. Shoot uptake of
    trifluralin by foxtail millet and proso milet was
    more efficient than was root uptake.

148
  • Carbamates
  • Some carbamates herbicides are characterised
    by low water solubilities. They are normally
    soil-applied, root-absorbed compounds having
    little phytotoxicity when applied to foliage.
    Other such as barban, phenmediphan and asulam are
    relatively water soluble and readily foliar
    absorbed.

149
Section 4 Biochemical mechanisms of action
  • The respiration process.
  • The mechanisms of respiratory metabolism is
    well known. Sugars are broken down to the
    three-carbon pyruvic acid which is subsequently
    degrade by a series of oxidative steps with the
    release of CO2 and electrons and H which unite
    with oxygen to form water. The electrons are
    transferred along an electron transport system
    from compounds of low reduction potential to
    those of higher reduction potential, O2 being the
    ultimate electron acceptor.

150
  • ATP Synthesis from ADPPi is coupled to this
    electron transfer, the process being termed
    oxidative phosphorylation. Apart from the
    glycolytic steps, these reactions occur under
    aerobic conditions in the mitochondria and many
    studies of the action of herbicide on respiratory
    metabolism have been carried out using isolated
    mitochondria. It is important that such
    mitochondria exhibit tight-coupling of
    oxidation and phosphorylation and should possess
    high RC(respirator control) and P/O
    (phosphorylation/oxidation) ratios.

151
Fig a simplified view of the steps involved in
glycolysis and the
Krebs cycle leading to ATP synthesis.
152
The action of herbicides on respiratory
metabolism
  • Haloalkanoic acids
  • These compounds appear to have relatively
    little effect on respiratory metabolism though
    conflicting views are evident from the
    literature. Foy and Penner (1965) found that of
    the chloro-aliphatic compounds which they
    investigated, only TCA had a noteworthy effect on
    succinate oxidation by cucumber mitochondria
    dalapon failed to inhibit succinate oxidation
    even at concentrations of 10-2-10-3 M.

153
  • phenoxyalkanoic acids
  • There is considerable evidence that these
    compounds act as uncouplers and inhibitor of
    oxidative phosphyorylation(Korkwood, 1976) and
    Moreland (1980) has tentatively them in the group
    known as inhibitor uncouplers.
  • Others, such as aromatic acids, nitriles,
    anilides, nitrophenols, nitroaniliens,
    carbamates, thiocarbamates, ureas, triazines,
    heterocyclic nitrogen compounds(unclassified)
    etc. they are also similar mechanism of action on
    their respiratory metabolism.

154
Inhibition of photosynthetic system
  • Electron transport inhibitors
  • Uncouplers
  • Energy-transfer inhibitors
  • Inhibitory uncouplers
  • Electron acceptors

155
The action of herbicides on photosynthesis
  • The haloalkanoic, phenoxyalkanoic and
    aromatic acids and amides, are generally regarded
    as ineffective on photosynthetic mechanisms
    except at high concentration and their primary
    mechanism of action is regarded as lying
    elsewhere. However, the hydroxybenzonittriles
    inhibit the Hill reaction and this together with
    uncoupling of oxidative phosphorylation appears
    to be primary mechanism of action.

156
  • Others
  • ? The action of herbicides on nucleic acid and
    protein synthesis
  • ? The action of
About PowerShow.com