Chapter 4 Fungicides

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Department of Plant Protection
School of Agriculture,Yangtze University
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.
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 1:3 in Africa, 1:5 in east Asia and 1:7 in Latin
American.
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.
Chapter 1 Basic Concept of Plant Chemical
Protection
1
2
3
4
5
Definition and Class of Pesticide
Toxic Power of Pesticide
Effects of Pesticide on Crop
Toxicity of Pesticide
Principles for Safety Application of
Pesticide
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
▲ Classification
◆ According to Source of Material and
Component:
Inorganic Pesticide:Sulphur,Aluminium
phosphide, Bordeaux mixture.
Organic Pesticide :
 Botanical Pesticide ;
 Oil Insecticide;
 Microbial Pesticide;
 Synthetic-organic Pesticide .
◆ Classified According to Use:







Insecticide;
Fungicide;
Herbicide;
Acaricide;
Raticide;
Nematocide;
Plant Growth Regulator
(Hormone mimics).
● Classification of Insecticides
1. Stomach poisons;
2. Direct contact poison ;
3. Fumigant;
4. Inner absorbent;
5. Antifeedant;
6. Repellentant;
7. Attractant.
● Classification of Fungicides
1. Protective fungicides;
2. Therapeutic fungicides;
3. Eradicant fungicides.
● Classification of Herbicides
1.
2.
3.
4.
Conducting herbicides;
Contacting herbicides;
Selecting herbicides;
Extinguishing herbicides.
Section 2 Toxic Power of Pesticide
Concept of toxic power of pesticide
Measurement of toxic power
Calculation of pesticide effects
Insecticide
Fungicide
Herbicide
Concept of Toxicity and Control Effects of
Pesticide
Toxic power:A measurement used as evaluated and
compared index, which was generally
determined under strict condition with insect,
bacteria or weed by precision method.
Control effects:Resulted from pesticides and multi
factors ,which was determined under field
condition.
Toxicity:Generally refer to mammal and human
being.
Measurement of toxic power of pesticides
1.Unit shows toxic power:
(1)Lethal Dose :LD50
(2)Lethal Concentration: LC50
(3)Effective Dose:ED50
(4)Effective Concentration EC50
(5)Knock-down Time: KT50
(6)Inhibition Concentration, IC50
2.Relative Toxicity Index
Calculation of Effects of Insecticides

Calculation of adjusted mortality:
Adjusted mortality 


(X  Y)
 100
Y
Where:X express percent survival in the untreated
controls;Y 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.
Calculation of Control Effects of Insecticides
 Ta C b
Control effects  1  
 Tb C a

  100

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.
Calculation of Control Effects of Herbicides
Qb  Qa
Control effects
 100
Qb
Where Qa express the weed quantity in the
treated controls; Qb express the weed quantity in
the untreated controls.
Section 3 Effects of Pesticide on Crop
▲ Damage of pesticide on the crops
1
2
3
4
Property of pesticides
Crop species,growth stage and physiological status
Environmental conditions
Symptom of damaged crop
A. Acute symptom B. Chronic symptom
▲ Stimulate effects of pesticide on the growth of plant
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.
K
Ca
 100
Cb
Where K means safety index; Ca express the
minimum concentration needed to prevent pest
damage; Cb express the maximum concentration that
plant can endure.
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.
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..
Acute Pesticide Damage
Acute symptom of pesticide damage
emerged in a short period,even in hours after
application of pesticides.
Chronic Pesticide Damage
Symptom of Chronic pesticide damages
emerged slowly,it need a long time period or
multiple application of pesticides.
Stimulating Effects of Pesticide on Growth of Crops
Tobacco formulation can improve the growth
of paddy;derris 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.
Section 4 Toxicity of Pesticides
Definition of toxicity of pesticides
Classification of toxicity of pesticides
Acute toxicity
Subacute toxicity
Chronic toxicity
Definition of Pesticide Toxicity
Toxicity:The 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.
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.
Domestic temporarily classification standard of acute toxicity of pesticides
Approach
Oral(mg/kg)
Dermal(mg/kg)I
nhale(mg/kg)
ⅠHigh toxicity
ⅡModerate toxicity
Ⅲ Low toxicity
<50
<200
<2
50~500
200~1000
2~10
>500
>1000
>10
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.
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.
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.
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.
K
Ca
 100
Cb
Where K means safety index; Ca express the minimum
concentration needed to prevent pest damage; Cb
express the maximum concentration that plant can
endure.
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
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
Concept of dispersing system and dispersing of
pesticide.
★ Dispersing system of pesticide:solid/solid ,
liquid/liquid,solid/gas, liquid/gas and
gas/gas dispersing system.
★ Concept of dispersing of pesticide: the
dispersed grade of pesticide .
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.
Section 2 Adjuvants
Class of adjuvants
Fillers,carriers:kaolin, bentonite;
Wetting agents:BX, detergent powder;
Emulsifiers;
Solvents:benzene, toluene;
Dispersing agents: surface-active agents;
Stickers: glutin;
Stabilizers;
Synergists: SV1.
Structure and Effect of Surface-active agents
Structure of surface-active agents (amphiphilic
compound)
Anionic surface-active agents
Hydrophobic part Hydrophilic part
Cationic surface-active agents
Hydrophobic part Hydrophilic part
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.
Surface-active phenomena
Effect: Reduce surface tension
Interface
Air
Liquid
Make spray drop more fine
Application in the processing of pesticide
As emulsifiers used in emulsifiable concentrates.
Oil
water
Oil
water
Oil
As wetting agents used in wet table powders .
Enhance the adherence ability of pesticide on
sprayed surface.
Class of surface-active agents
Anionic SAA
Cationic SAA:Organic amine
Amphiphilic SAA:ester and aether
Nonionic SAA
Natural SAA
Anionic SAA:Widely used, such as sodium dodecylbenzene sulphonate, such as calcium dodecylbenzene sulphonate.
R
SO 3 N a
Sodium dodecyl-benzene sulphonate
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
◆ Dusts
Constitute:Technical products and carriers.
Standard:95% of pesticide can sieve through
0.074 µm mesh screen.
Characteristic:easy to use;need no water;high
efficiency.
Shortcoming: pollute environment;bad control
effects.
◆ Granules
Constitute:Technical products,adjuvants and carriers.
Classification:macrogranules;granules;microgranules.
Standard:90% can match the standard of particle size;
moisture content<3%.
Characteristic:lower toxicity of high grade toxic
pesticides in use;controlled release;easy to use;
reduce pollution.
◆ Wettable powders
Constitute:Technical products,wetting
agents,dispersing agents and carriers.
Classification:macrogranules;granules;micro
granules.
Standard: moisture content<3% ; pH=5~9;
wetting time:1-2min;particle diameter:3~7
µm ;suspension rate:>70%.
Characteristic:high develop quality.
◆ Soluble powders
Constitute:Technical products,wetting
agentsand carriers.
Standard: moisture content<3% ; wetting
time:2-3min.
Should pay attention to distinguish the difference
with wetting powders.
◆ Suspension concentrates and
colloidal formulations
Suspension concentrates:
Constitute:Technical products and multiadjuvants.
Standard: particle diameter:0.5~5 µm ;suspension
rate:>90%.
Colloidal formulations:
Constitute:Technical products and multiadjuvants.
Standard: particle diameter:0.01~0.1 µm ;should be in
colloidal condition in liquid.
◆ Emulsifiable concentrates
Constitute:Technical products,solvent, emulfiers
and cosolvent.
Classification:stock emulsions, aqueous
solutions, emulsifiable concentrates.
Characteristic:high control effects.
Shortcoming :consume a great deal of organic
solvent,pollute environment, have trouble in
transportation.
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
device;7. filtration device; 8.container of emulsifiable concentrates;9.products
packaging
◆ 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.
Attention:seed coatings is different with seed
treat concentrates.
◆ 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.
Characteristic:generally contain 20~50% of effective
component,can be used with no more dilution.
Should pay attention to distinguish the difference of
EC,SE,AS and OS.
◆ 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 formulations:integrate
with chemical reaction.
◆ Function of Controlled Release Formulations



Lower toxicity of high grade toxic pesticides in
use.
Prolong effective period of pesticides.
Decrease applied quantity of pesticides.
◆ Smokes
Pesticide formulation when ignited,the effective
component of pesticides suspending in
dispersing state like smoke in air.
Constitute:Technical products, fuel(varied
carbohydrate),oxidant and extinguish agents.
Section 4 Pesticide Application Methods
Spraying
Dusting
Other application methods
Application on mixed pesticides and Synergist
Calculation of co-toxicity coefficient
Synergist
◆ 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.
◆ 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.
◆ Other Application Methods ◆
Spread and slosh irrigating;
Soil spraying;
Seed milling;
Seed immersing;
Poison lure;
Fumigating.
Application on mixed pesticides and Synergist
Calculation of co-toxicity coefficient
Toxic index of pesticide A(K A) 
LD50 of A
 100
LD50 of A
Toxic index of pesticide B(KB ) 
LD50 of A
 100
LD50 of B
Toxic index of pesticide B(KC ) 
LD50 of A
 100
LD50 of C
Practice toxic index of mixed pesticide (K M ) 
LD50 of A
 100
LD50 of M
Academictoxicindex of mixedpesticide(KM )  KA  PA  KB  PB  KC  PC
Co - toxicity coefficien t (CTC) 
practice KM
 100
academice KM
Class of synergist and synergistic effects
Pb
Sesamin
Application via plane



Advantages and disadvantages of application
by plane;
Equipment of dusting and spraying;
Manner of spraying:
 Placement spraying;
 Incremental drift spraying.
Chapter 3 Insecticides
1 Botanical insecticides
2 Synthetic insecticides
miscellaneous and organ chlorine compounds
organ phosphorus and carbamate compounds
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.
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.
(1)
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.
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. It`s molecule
structure is :
ROTENOIDS
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.
Gem-dimethyl
group acid
alcohol
Compounds
R`
R
Pyrethrin
-CH2=CH2
-CH3
Pyrethrin 2
-CH2=CH2
-CO2CH3
Cinerin 1
-CH3
-CH3
Cinerin 2
-CH3
-CO2CH3
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.
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.
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.
Organochlorine insecticides
The most important member of this group of
insecticides is 1,1,1-trichloro-2-2-di-(pchlorophenyl)ethane also termed
dichlorodiphenyltrichloroethane 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.
DDT is manufactured by condensation of chloral
chlorobenzene in the presence of an excess of
concentrated sulphuric acid:
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:
◆ 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:
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 tetramethylphosphorodiamidic
fluoride or dimmefox, while in Germany Schrader made
the hignly active nerve gases tabun and sarin.
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.
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.
Others is also high mammalian toxicity insecticide
such as :
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.
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
Fig A
Fig A depicts the formation of the initial enzymesubstrate 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.
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.
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 ionimpermeable 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-3methylpyrazolyl-5-dimethylcarbamate).
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.
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.
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 nonselective insecticides often eliminated many of the natural
predators.
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.
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.
The addition of synergists is also often helpful in
overcoming resistance; for instance, DDTdehydrochlorinase inhibitors such as WARF antiresistant:
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 dimethoateresistant insects can be inhibited by methylene
dioxyphenyl synergists themselves which can
substantially reduce the effectiveness of synergistinsecticide mixture.
Chapter 4 Fungicides
1
2
3
4
The
The
The
The
story of fungicides
nature of fungicides
Inorganic fungicides
Organic fungicides
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.
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.
◆ 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.
◆ 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 1600`s regularly practiced dipping seed wheat from
Australia in ocean water for bunt control. This is the first example
of seed protection with chemicals.
◆ Fungicides in the 20th century(19001930):
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. Scott`s selfboiled lime-sulfur was made by slaking together 15 pounds
of quicklime and 10 pounds of finely divided sulfur
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.
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.
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.
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.
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.
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.
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.
◆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.
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
4 lbs, lime
50 gals water
4-4-50
means
4 lbs, CUSO4 5H2O
4 lbs, lime
50 gals water
1/2-3-100
means
1/2 lbs, CUSO4 5H2O
3 lbs, lime
50 gals water
10-10-100
means
10 lbs, CUSO4 5H2O
10 lbs, lime
50 gals water
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
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.
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.
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 1920`s to accelerate the action of sulful in
vulcanizing rubber.
This acid represented by the structural formula:
The fungicidal derivatives of this compound
may be classified into three group:
(1) thiuram disulfides :
Foe example:tetramethylthiuram disulphide(common
name:Thiram)
(2) metallic dithiocarbamates:
(3) ethylene bisdithiocarbamates:
The metallic dithiocarbamate fungicides are
characterized by the folloeing structure formula:
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”.
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
Several kinds of fungicides data:
Common name: nabam
Chemical name: disodium ethylenebisdithiocarbamate
Empirical formula: C4H6N2Na2S4
Chemical and physical properties:
molecular weight:256.3 melting point:decomposes before
melting physical state: solid color: white flammability: noncomlustible, but may form combustible decomposition products
solubility: relatively unstable to heat, light and moisture but
solution are stable.
toxicity:oral to mammals acute LD50 395mg/kg, chronic
1000-2500ppm in diet of rats produced
goitrogenic effect in 9-10 days
FDA tolerance:7ppm on fruits and vegetables
Common name: zineb
Chemical name: zinc ethylenebisdithiocarbamate
Empirical formula: C4H6N2S4Zn
Chemical and physical properties:
molecular weight:275.7 melting point:decomposes
physical state: powder color: white to off-white
flammability: flash point 280-290℃, solubility: soluble in
pyridine; solubility in water over 10ppm. toxicity:oral 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.
Common name: maneb
Chemical name: manganese
ethylenebisdithiocarbamate
Empirical formula: C4H6MnN2S
Chemical and physical properties:molecular
weight:265.3. melting point:decomposes 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.
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.
The glyoxalidine Nucleus is a hetero-cyclic ring
compound more correctly referred to as an
“imidazoline” nucleus. It`s nucleus is represented
as:
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 point:62-68 ℃. 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
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, it`s wide chemical
reactivity of this group is undoubtedly important in
their fungicidal activity. e.g. benzoquinone,
naphthoquinone etc.. The molecular structure viz.:
The Application technique of fungicides:
a. Kittleson`s 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
Chapter 5 Herbicides
1
2
3
4
5
Introduction
Classification
Use of herbicides
mechanism of action
herbicide and environment
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.
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.
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)
●Haloalkanoic acids:
for example: sodium trichloroacetate(CCl3COONa)
dalapon(CH3CCl2COOH)
Sodium chlorate(NaClO3)
Chlorfenprop-methyl
●Phenoxyalkanoic acids
●Phenoxyacetics
●Phenoxybutyrics
●Phenoxypropionics
●Aromatic acids
●Amides
●Nitriles
●Anilides
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-ocresol(1;R=CH3)(DNOC or Sinox) in France in
1933.
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.
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.
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 14Cdiphenamid 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 .
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.
Nitriles
In contrast to the hydroxybenzonitriles,
dichlobenil and chlorthiamid are essentially preemergence 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).
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.
Nitrophenyl ethers
In this group of compounds nitrofen, fluorodifen,
chlornitrofen and acifluorofen may be applied pre- or postemergence, 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.
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.
Carbamates
Some carbamates herbicides are characterised
by low water solubilities. They are normally soilapplied, 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.
Section 4 Biochemical mechanisms of action
The respiration process.
The mechanisms of respiratory metabolism is
well known. Sugars are broken down to the threecarbon 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.
ATP Synthesis from ADP+Pi 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.
Fig a simplified view of the steps involved in glycolysis and the
Krebs cycle leading to ATP synthesis.
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 chloroaliphatic 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.
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.
Inhibition of photosynthetic system
Electron transport inhibitors
Uncouplers
Energy-transfer inhibitors
Inhibitory uncouplers
Electron acceptors
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.
Others:
★ The action of herbicides on nucleic acid
and protein synthesis
★ The action of herbicides on lipid synthesis
Metabolism of herbicides
Degradation mechanisms in plants
Herbicides degradation in higher plants may result
from a wide range of chemical reaction, most of
which are catalysed by specific enzymes though a few
appear to be non-enzymatic in nature. The various
types of reactions have been reviewed by Ashton and
Crafts(1973) and include oxidation, decarboxylation,
deamination, dehalogenation, dethioation,
dealkylation, dealkyloxylation, dealkythiolation,
hydrolysis, hydroxylation and conjugation
mechanisms.
Section 5 herbicides and environment
Legislation and the use of herbicides
Conditions governing the registration of pesticide(include
herbicide) vary from country to country but most highly
industrialised countries lay down stringent conditions that
must be met before a particular pesticides can be marketed.
All European countries with the exception of the U.K. ,
prohibit by law the salt of any pesticides unless it has been
registered for the specific used described on the
manufacturer`s instruction label.
In the United Kingdom the pesticides safety
Precautions scheme-non sattutory was drawn up in
negotiation between the ministry of agriculture, fisheries
and food, the then ministry of health, the corresponding
Scottish departments and the industrial associations
concerned. Its purpose is to safeguard human beings
against risks raising from the use of pesticide. Under the
Scheme, distributors proposing to introduce new pesticides
and new uses of pesticides in the U.K. are required:
1. To notify such new pesticides to departments
2. To ascertain and disclose such information as may
be required by the departments to enable them to
advise on precautionary measures
3. Not to introduce such compounds until agreement
has been reached on appropriate precautionary
measures
4. To include the agreed precautions and the British
standards institute common name (or chemical
name) of the active ingredient on the label
5. To notify any substantial change in the text or
layout of the label
6. To withdraw a product if recommended to do so
by the department
The Scheme applies to all active ingredients
formulated as pesticides, I.e. insecticides, herbicides,
rodenticides, and similar substances. Full details of the
Scheme may be found in a pamphlet drawn up by the
ministry of agriculture, fisheries and food. Included also
is a toxicity data guide offered as a guide to notifiers
who wish to present adequate data ona product`s
toxicity. The properties of a chemical that may be
investigated include:
1. The physicochemical properties which would
influence risks in the filed or persistence as a residue.
2. Acute toxicity; LD50 values by single doses and
apparent mode of toxic action
3. Skin penetration and absorption; percutaneous toxicity;
irritancy of liquid or vapour to body surface
4. Cumulative effects of known functions of LD50 values
over short periods representative of user exposures
5. Effects arising from prolonged exposure, chronic toxicity
6. Delayed effects, arising usually after a silent
development period.
7. Metabolic studies
8. Potentiation of, or by, other toxic chemicals under special
circumstances
9. Diagnostic and therapeutic possibilities.
● Others affects of herbicides
Herbicides and micro-organisms
The persistence of herbicides in soils
Effect of herbicides on fish
Effect of herbicides on birds and their
eggs
◆ Effect of herbicides on mammals
◆
◆
◆
◆
Chapter 6 Plant Growth Regulators
1 Introduction
2 Classification
3 Use of plant growth regulators
Section 1 Introduction
Auxins-natural and synthetic:
Although there had been speculation about the presence of
substances with plants which correlated their growth and Sachs
in the later half of the 19th century put forward the idea of
`organ-forming substance` it was the publication by Darwin of
his book THE POWER OF MOVEMENT IN PLANTS In 1880 that
led eventually to the isolation of plant to hormone. Darwin
reported on his studies of the responses of plants to light and
gravity. It was indeed a plant hormone which has been defined
as `an organic substance produced naturally in higher plants,
controlling growth or other physiological functions at a site
remote from its place of production and active in minute
amounts`.
At present, PGR be used to include both `natural
auxins` for those produced by plants themselves and
`synthetic auxins` which have the same action as
natural auxins but which do not occur naturally in
plants but are synthesized in the laboratory.
For example:
indolyl-3-acetic acid(IAA)、 3-acetonitrile(IAN)、
4-[indol-3-yl]butyric acid(IBA)、a-naphthylacetic
acid(NAA)、2- naphthyloxyacetic acid(NOA)、1naphthylacetamide(NAD)
Phenoxyalkanoic acids are best known and
most widely used for their selective weeding
properties but sublethal doses of 4-CPA、2-4-D、
2,4,5-T and fenoprop are used as growth
regulators to promote fruit set and for
thinning.2,4-D has also been shown to increase
the dry matter and yield of potatoes, peas, beana,
corn and sugar-beet.
Auxins-structural formulae:
(IAA)
(NAA)
(IBA)
(NOA)
(NAD)
Section 2 Classification and use of PGR
Gibberellins
Cytokinins
Ethylene
Etacelasil
CGA-15281
Growth inhibitors
■ Gibberelins:
There are more than fifty occurring gibberellins.
Commercial formulations are used for breaking
dormancy, flower iniation, promoting vegetative and
fruit growth and for the induction of parthenocarpy.
Paleg(1965) has defined gibberellins as `compounds
having an entgibberelance skeleton and biological
activity in stimulating cell division or cell elongation, or
both, or such other biological activity as may be
specifically associated with this type of naturally
occurring substance`.
More than fifty Gashave been isolate from the tissues
of various plants and HEDDEN et al. (1978) have
published their structural formulate. Rather than give
these gibberellins trivial names they have been
designated as GA1,GA2,GA3,etc. gibberellic acid is GA3. No
plant has been found which contains all of the gibberellins
but most plants-angiosperm, gymnosperms, ferns, algae,
fungi and bacteria-possess several of them. Because of
the complex structure of the GAs it has not been possible
to synthesis substances of comparable activity but several
gimbberllins can Be produced commercially by large-scale
fermentation and they are available for horticultural and
agricultural use.
■ Cytokinins:
Cytokinins may be natural(zeatin) or sysnthetic
(e.g. kinetin). Zentin affects cell division and leaf
senescence and synthetic cytokinins are used to
promote lateral bud development and inhibit
senescence. The discovery of cytokinins came
about as result of investigations into the growth of
plants tissue cultures. Later other adenine
derivatives were found which had similar biological
activity and they were referred to collectively as
kinins, a name which has later changed to
cytokinins properties.
Because animal physiologists and a prior claim
to the term kinin referring to a class of polypeptides
which had quite different properties. Kinetin has
never been found in plants but it is clear that some
cytokinins are widely synthesized in plants. They are
found particularly in young and actively dividing
tissues such as embryos, seedlings, and
apicalmeristems. Whether or not these are the sites
of synthesis is still open to question science it is
possible that they are synthesized elsewhere and
translocated to these sites.
A large number of compounds based on kinetin
have been synthesized and tested for cytokinin
activity and some of them were more powerful
than kinetin itself.
Cytokinins-structural formulate:( for example)
Kinetin
Zeatin
■ Ethylene:
Ethylene gas is produced naturally in plant
tissues often in response to environmental stress or
wounding and also during ripening ripening and
abscission processes. Synthetic ethetic ethylene
generators(mainly ethephon) are used to induce
fruit abscission, promote of female flowering and
fruit ripening, break dormancy, increase production
of female flower in cucumbers and melons, thin
grapes and stimulate latex flow in rubber trees.
Ethylene is a rather unusual plant hormone in that it
is gaeous and is a very simple organic molecule. It is
however a very active one and at very low
concentration can have profound effects. In 1967,
which when applied liberates ethylene into plant cell,
has led to a wide range of commercial applications. A
very important application of ethylene is in its used to
increase the duration of latex flow in rubber trees.
Ethephon is also a powerful abscission-promoting
agent which is used for thinning heavy cropping
cultivars may be harvested early to benefit from early
market prices by treating them about 10 days before
picking.
Ethylene-releasing compounds-structure formulation:
Ethylene
Ethyephon
Etacelasil
Glyoxime
CGA 15281
■ Growth inhibitors
There are many natural inhibitors found in plants of
which abscisic acid and the closely related xanthoxin
are the best known: they have not found commercial
application but are used as research tools. For
example:
Abscisic acid(ABA) (penta-2,4-dienoic acid –5-[1hydroxy-2,6,6-trimethyl-4-oxoclohex-2-en-1-yl]-3methyl)
Abscisic acid (ABA)
ABA has a wide range of physiological effects
when applied externally. It will induce abscission
of petiole bases in explants of cotton seedlings
and induce rapid senescence of leaf discs of
various species (through less so in intact plants).
It is believed to play an important part in the
dormancy of buds and certain types of seeds.
★ synthetic growth inhibitors and retardants
The seach for new chemicals which inhibit or
retard growth is a very active filed of research.
Some are though to act by inhibiting gibberellin
synthesis, other by inhibiting terminal or lateral bud
development affected by auxin distribution. Some
are used to reduce the height of cereals and thus
prevent lodging, some to retard the growth of
grasses and shrubs, some to interfere with apical
dominance and thus change the shape of a plant,
some as defoliating agents and some to prevent
sucker(axillary bud) development.
For example:
Maletic hydrazide(MH)
Daminozide
Glyphosine
Ancymidol
Chlorphonium chloride
Morpholinium chloride
4-methoxybenzophenones
Piproctanyl bromide
Thidazuron
etc.
Chapter 7 environmental toxicology
of pesticides
1. Insecticide residues and biotic food chains
2. Herbicides: persistence and plant ecosystem
effects
3. Fungicides and the soil microflora
4. Basic of pesticide residue analysis and
quality of residue data
Section 1 Insecticide residues and biotic
food chains
1. Fate of residues in the biota:
Uptake of insecticides from water
Microorganisms. The algae and bacteria in the
water are very efficient concentrators of
insecticides, their small size and consequently
high surface-to-mass ratio making for rapid and
thorough adsorption.
2. Relation to food chain:
The direct accumulation of the organochlorine from
the water can in certain case make the additional uptake
from the food irrelevant. Reticulated sculpins exposed to
dieldrin in laboratory squatic took up the same amount of
the insecticide whether or not the tubifex worms on
which they were fed were contaminated with dieldrin.
Smallmouth bass fingerlings in artificial pools treated with
DDT took up as much of this organochlorine when the
aquatic invertebrates inhabiting those pools were
replaced as a fish-food sourced by brine shrimp
separately reared free of DDT.
Food chains:
Aquatic food chains. The first fully developed example
of the poisoning of birds through the food chain emerged
when DDT was applied to clear lake, California in 1957.
The recreation amenities of this 75 sq mi warm shallow
eutrophic lake were severely handicapped by its producing
large numbers of the clean lake gnat, Chaoborus astictopus.
DDT was, therefore, chosen to control the aquatic larvae of
this pest species, and treatment of the entire lake in 1949
with an average concentration of 14ppb achieved 99%
control without killing any of its considerable fish
population.
3. Food chains residues in untreated area:
By the close of the 1960s. residues had become a
problem even in areas which had not been treated at all.
Sample of northern pike and mussels taken in 1967 and
1968 in untreated areas of north Atlantic countries revealed
0.01-0.03ppm in the soft tissue of the mussels, and 0.022ppm in the lateral muscle of the pike: the highest residues
in the pike were in Italy and the highest in mussels were in
Modiolus demissus in the united states.
4. Model Ecosystems:
A means of following the fate of an insecticide as it
reaches the aquatic sink, and of obtaining a comparative
assessment of its biomagnification or biodegradability, is
offered by the model ecosystem of Metcalf(1974). A stand
bed in an all-glass aquarium measuring 25×30×45cm is
graded so that half is a pool, while the other half is sown to
sorghum, which when it has grown to 10cm height is
treated with 5mg of the radio-labeled insecticides under
investigation. It is then artificially infested with 10 large saltmarsh caterpillars, and the water is colonized with a
filamentous green alga, and sometimes with the water weed
Elodea.
Section 2. Herbicides: persistence and
plant ecosystem effects
1. Herbicides effects on the plant ecosystem
The essential role of herbicides in crop production is
to protect monocultures, and to prevent the bared arable
land from being overgrown by plant cover natural to the
site and climate. The various chemicals employed have a
certain selectivity from one seed-plant group to another,
certain being effective against grassy weeds in broadleaf
crops, and others effective against broadleaf weeds in
cereal crop.
◆ Long-term effects of single application
grassland
forest
◆ effects of continued application
field crop weeds
orchard weeds
effect on prthogenic fungi
Plant resistance to herbicides
Preexisting natural tolerance
The especial tolerance of fall panicum and green
foxtail to atrazine in cornfields was due to these weeds
absorbing less of the herbicide than the crop to be
protected, but the situation could be corrected by a
postemergence spry with another triazine, namely
cyanazine developed by the continued use of
atrazine,since fall panicum from untreated area was
found to be no more susceptible than the treated
problem areas in New Jersey.
Development of resistant populations:
While the preexistence of refractory ecotypes
provides a potential source of populations resistant
to herbicides, there are three examples of
herbicides-resistant strains having developed in
response to selection pressure in the sense that
they have become increasingly difficult to control
with each successive application of that
herbicides(table)
Example of weed populations resistant to herbicides:
Emergence of resistant population
Erchtites hieracifolia
(hawiian fireweed)
2,4-D
Hawii 1955
Cirsium arvense
MCPA
Norway 1973
Poa annual bluegrass Metoxuron
France 1974
Existence of resistant ecotypes
Setaria lutescens
(Yellow foxtail)
Dalapon
Maryland 1960
Cirsium arvense
(Canadad thistle)
Amitrole
Idaho 1970
Sorghum halepense
(johnson grass)
Dalapon
Arizona 1963
2. Persistence of herbicide residues in the soil
(1) Disappearance and degradation:
Unlike some of the persistent pesticides,
residues of herbicides do not build up from
one year to the next, since at the dosages
used on croplands very few persist in the soil
for more than 12 months.
(2) Disappearance and translocation:
Additional factors governing the disappearance
of residues include volatilization,
photodecomposition, adsorption and leaching as
explained in detail in the reviews of Helling,
Kearney, and Alexander and of Weber and Weed,
and summarized in the book by Klingman and
Ashton.
Section 3. Fungicides and the soil microflora
1. Persistence of fungicides in soils
A number of simple organic compounds are applied
to greenhouse soil and seedbeds to control root-rot
and damping-off fungi, as well as nematodes and soil
insects. These include methyl bromide and chlorocrin
etal.. Recent countermeasure to overcome the residue
problem with mercurials and the resistance problem
with the benzimidazoles have been the development of
certain organophosphorus compounds as fungicides,
particularly for powdery mildews, examples are
triamiphos and Dowco 199(diethyl
phthalimidophosphorothioate).
2. Effects of fungicides on soils
The materials developed as fungicides have been chosen
for their lack of phytotoxicity to higher plants. Even the
copper fungicides, which accumulate in the soil year after
year, had no effect on the growth of apple trees and grass
cover in orchards of eastern England. However, frequent
spraying with Bordeaux mixture resulting in soil
accumulations reaching 300ppm Cu has adversely affected
vegetable crop.
3. Fungicides: effects on Invertebrates
and vertebrates
(1) Effects on invertebrate fauna
Arthropod predators and parasites in orchards
Past experience and test
Hymenopterous parasites
Predaceous mites
(2) Hazards of fungicides to vertebrates
Mercurial seed dressings
Mercurial in food chains
other fungicides
Section 4. Basic of pesticide residue analysis
and quality of residue data
1. Chromatographic application in pesticide residue
analysis:
Chromatography is a separation science, which
encompasses both a stationary phase and a moving
phase which separates the components of a mixture. In
principle, there are four types of chromatography which
are as follows:
(A) Ion exchange chromatography. (B) Exclusion
chromatography, (C) Adsorption chromatography, (D)
Partition chromatography
Pesticides residue extraction and
cleanup
Extraction :
In order to extract residues from food products, the first
step is to mechanically reduce the size of the food product.
A know amount of the product is then weighted into a
blending jar for organic solvent extraction. These solvent
are popular choices for extraction purpose, but advantages,
but advantages and disadvantages must be understood for
proper use.
Solvent properties:
Based on the data from Snyder`s study of
eluent strength function with alumina
adsorbent, the sequence of solvent eluotropic
strength is acetonitrile> ethyl acetate>
acetone> dichloromethane. These studies
provide vital information for the proper
utilization of various solvents in extraction.
Methods:
Cleanup
Matrix cleanup is probably the most difficult
subject in the food crop testing field as
uncountable crop species, growth or maturity
stages, weather conditions and soil type, all
introduce complexities in tissue compositions to
be encountered.
Cleanup procedures are based on the four
chromatographic mechanisms:
A. Liquid-liquid partition
B. Ion exchange
C. Gel permeation chromatography(GPC)
D. Bonded silica sorbents or solid phase
extraction(SPE)
1. Pesticides residue analyses by gas
chromatography
2. Pesticides residue analyses by liquid
chromatography
3.confirmatory analysis:
a. different columns: different polarity
column
b. different detectors: GC/MS and LC/MS
c. different method: GC-NPD, GC-FID GCECD
2. Quality of residue data:
(1) Development of quality requirements of chemical
analysis:
A. Reliable analytical results
B. Reliable studies
C. Total quality management
(2) Room for improvement of the quality of residue data:
A. effect of sampling on the uncertainty of
residue data
B. effect of sample preparation
C. evaluation of calibration curves
D. correction for the average recovery
E. optimisation of residue analytical procedures
(3) Summary of conclusions and recommendations
Chapter 8 Pesticides Future developments
1. The current of the times of modern
pesticides
2. The new ideas of the modern pesticides
development
Section 1. The current of the times of
modern pesticides
The original chemical pesticides were general poisons with
non-specific activity; thus early herbicides like sodium chlorate
and copper sulphate were total weed killers which could not
be effectively applied as selective herbicides. Likewise
insecticides such as hydrogen cyanide, lead arsenate, and
Paris Green were highly poisonous materials with a wide
spectrum of insecticidal and mammalian toxicity.
Similarly, such fungicides as sulphur, Bordeaux mixture and
Organomercurials tended to be comparatively non-specific in
their toxicity towards fungi.
Later work led to the discovery of less poisonous and more
selective organic chemical pesticides; illustrative example were
the phenocyacetic acid selective herbicides, certain
organophosphorus insecticides like malathion, and the
trichloromethylthio fungicides, e.g. captan.
There is now much greater awareness of the dangers of
environmental pollution arising from the widespread
application of chemical pesticides, and residue formation
before they can be marketed as pesticides in many countries.
This has caused research on new pesticides to be increasingly
concerned with producing chemicals which are safer and more
selective in their action.
The ideal chemical pesticide would have high specific
toxicity against the target pest , should not persist longer
than necessary to achieve its objective, and would not affect
the rest of the ecosystem, so that natural predators and
other beneficial insects are unharmed. Some well-known
examples approximating to these criteria are the systemic
fungicides, such as dimethirimol, which shows high selective
activity against cucumber powdery mildew. Remarkably
potent specific toxicity against flying insects has also been
achieved with some synthetic pyrethroids such as
decamethrin. However, the majority of pesticides currently in
use fall far short of these ideals.
The availability of more selective chemical pesticides
permits them to be used in conjunction with biological control
methods and it seems probable that integrated biologicalchemical measures of pest control will become more common
in the future. Such procedures as manipulating the ecology of
host and pathogen, while reserving chemical treatment until
the other measure have at least reduced the severity of the
pest attack, allows the pest to be controlled effectively by
smaller amounts of the often costly chemical. It would was
have the advantage of reducing the danger of environmental
pollution. The plan breeder has been very successful in
producing new strains of crop plants with genetic disease
resistance against sedentary root pathogenic fungi, but so far
this approach has been less effective in combating the rapidly
dispersable foliage fungi.
In conclusion there appears little prospect in the
foreseeable future that biological control measure, such as
the introduction of resistant crop varieties, cultural control,
genetic methods, or the use of natural predators will
displace chemical pesticides from their dominant position.
However, further research on these and other biological
control measures is very necessary, to improve their
efficiency and enable them to be increasingly employed in
integrated control programmes in conjunction with chemical
pesticides. The most productive areas of research probably
lie in the fields of behaviour-controlling chemicals , microbial
pesticides, plant viricides and bactericides, and systemic
fungicides, especially those active against Phycomycetes.
Section 2. The new ideas of the
modern pesticides development
1. Generic biological screening to new
pesticides
2. High throughput screening to new pesticides
3. Combination chemistry
Biorational molecular design
(SAS 2D or 3D-QSAR)
For example, some new production were developed
through the idea of QSAR:
bromobutide:
bifenthrin:
ipconazole:
Others idea to develop new pesticides :
1. Genomics
2. Computational biology
3. Biopesticides
4. Green chemistry
5. Complementary molecular reactivity/
molecular recognition(CMR/R)
The methods of analyzing to the new compound
The current of the times :
The main measure of analysis and detection are
instrument, for example :
Infared spectroscopy, IR
Ultraviolet-visible, UV-Vis spectroscopy
Nuclear magnetic resonance, NMR
Mass spectrometry, MS
Gas liquid chromatography, GLC
High performance liquid chromatography, HPLC
Chapter 9 Resistance to pesticides
1. The introduction of resistance to pesticides
2. The countermeasure to bring resistance by
biology to pesticides
Section 1. The introduction of resistance to
pesticides
The development of resistance to insecticides by
many insect species is an important phenomenon. Pest
species change genetically under regular use of
pesticides. Resistance develops in populations
possessing resistant genes. These individuals survive,
propagate, and repopulate the species. Georgopoulos
started that 137 species of mites, insects, and other
other arthropods had been reported as developing
resistance to insecticides as early as 1960.
The changes developed very fast in some species.
This phenomenon was probably more important than any
other factor in convincing entomologists to move to
integrated pest management programs that minimize the
use of chemical pesticides where possible.
Fadeev has report a technique to partially circumvent
the development of resistance to specific pesticides by
insects and mites. He recommends alternating the use of
as many pesticides as are effective to avoid constant use
of one. He reports much less development of resistance
by this technique.
In Asia only a few example of insect resistance
to insecticides have been report(R. Smith 1972).
Most are based on circumstantial evidence alone
and the documentation is not as careful as it should
be. Several chemicals used against the
diamondback moth, Plutella maculipennis, which
attacks cruciferous crops, are now becoming
ineffective.
Another attendant result of prolonged pesticide
use has been the buildup of previously minor pest
species. Several well-documented reports are
available on cotton in Asia and on tea in Sri Lanka.
The development of resistance is an important
possibility in plant disease organisms and other
pests. Thus far only a small number of fungi are
known to be resistance to fungicides: “in the field ,
fungi have rarely developed economically important
resistance in farmer`s crop . In the laboratory they
often do. The general theory for this is that most
fungicides have a broad spectrum of activity. Some
fungicides seem to have a limited spectrum of
activuty and resistance has developed to these. ”
Section 2 The countermeasure to bring
resistance by biology to pesticides
Selectivity in pesticides and use:
Problem that were developing because of the
persistent insecticides and some other pesticides
largely brought about the integrated pest
management movement some years ago by
entomologists concerned about the excessive use
of pesticides. Metcalf summarized the problems
and emphasized the importance of developing
more selective methods of using insecticides in
more efficient, smaller dosages.
It must be remembered always that pesticides are
applied to the environment as purposeful contaminants.
Consequently, the benefits from their use must greatly
exceed any damage to environmental quality. Adequate
pest control can be achieved in most cases with lower
volume of applications more precisely timed and placed.
When economic factors severely limit the number of
applications of a fungicide or other chemical that can
profitably be given in a season, the applications must be
properly timed. If the chemical is applied too early it may
be wasted; of too late the damage may already have
been done. Good timing depends on good forecasting,
good knowledge of the disease progress curve and how
an alteration of the curve will reduce loss from disease.
Main reference book:
1. Sill. Webster H. plant protection. the iowa unversity press.
2. Can pingpan. Modern pesticide analysis. China agricultural
university press.
3. A.W.A.BROWN. Ecology of pesticides. A wiley-interscience
publication.
4. M. B. GREEN, G.S.HARTLEY AND T. F. WEST. Chemicals
for crop protection and pest control.
5. MANUEL C. MOLLES. ECOLOGY :CONCEPTS AND
APPLICATION.
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