This document discusses the chemical control of plant diseases and public concerns about pesticide use. It provides a brief history of major pesticides used before and after World War II, including metals, arsenites, pyrethrum, nicotine, organophosphates, DDT, and carbamates. It also classifies pesticides based on their chemical nature, targeted organisms, mode of action, and method of entry into the body.

1. CHEMICAL CONTROL OF PLANT
DISEASES AND PUBLIC CONCERNS
ABOUT THEIR USE.
Kamran Asif Khilji Roll Number : 04
Advancements In Plant Pathology
Institute of Agricultural Sciences
University of Punjab, Lahore

2. INTRODUCTION
 PEST:
“Any organism which competes with human being
for food, space and shelter is called as pest”
 PESTICIDE:
The chemicals used to control pests (undesirable
organisms) are called as pesticides.

3. Brief History of Major Pesticides
 Prehistory: Sulfur
 First seen in Egyptian writings 2400 B.C. and Chinese writings 1500 B.C.
 Greek writings
 700 BC

4. Before World War II
Metals and Salts
Arsenites. Paris Green,
A gem of a pesticide - copper acetoarsenite.
circa 1867 This was introduced and used first as
a pigment, known as Emerald Green, later as a
pesticide.
Other arsenic preparations and products of the dye
industry were also used
 Paris Purple
 London Purple

5. The Control of Other Pests
 Bordeaux mixture
 (copper sulfate and
hydrated lime)
 First effective fungicide,
1882
 Pierre M. A. Millardet,
 French National Hero

6. Before World War II
Lead Arsenate Very Important
Lead Arsenate to fight the gypsy moth 1892.
 Heavily used in much of agriculture
 Heavily used in apples
 Soil contamination remains a problem today in
many old orchard soils in the Northwest

7. Other Non-metalic Pesticides
 Pyrethrum
 A carefully held secret for many
years 1850-
 Source is Chrysanthemums
 Nicotine
 Widely used until WWII
 Extremely toxic
 (LD50 = 1mg/kg)

8. Discover of New Insecticides
 Discovery of organophosphates
 Gerhard Shrader: A German Scientist
 Attempting to replace Nicotine
 Developed organophosphate esters
 Tabun, sarin, soman (G gases), parathion
 First to be poisoned by nerve gas (tabun)

9. Discover of New Insecticides
 DDT
 First synthesized by a German
graduate student Othmar
Zeidler in 1873
 Rediscovered by Paul Mueller, a
Swiss entomologist, in 1939
 World War II, Use of DDT to
control typhus and malaria.

10. Paul Müller
Nobel Prize 1948
 “My fly cage was so toxic after
a short period that even after
very through cleaning of the
cage, untreated flies, on
touching the walls fell to the
floor. I could only carry on my
trials after a thoroughly
cleaning and after that leaving
it for about one month in open
air.” Muller Nobel Prize
acceptance speech 1948.

11. Classification of Pesticides
Classification of pesticides helps in understanding their chemistry and toxicology.
Pesticides can be classified on the basis of different parameters. These parameters
depend upon the requirement of the study to be conducted and the situation of
analysis. Categories falling in one type of classification may fall in another type of
classification.
The Pesticides are classified according to Singh. K. D 2012 depending upon ;
 Chemical nature of pesticides
 Targeted organism
 Mode of action of pesticides
 Method of entry into the body

12. Chemical Nature of pesticides
 Organochlorine compounds
The hydrocarbon compounds in which one or more hydrogen atoms are replaced by
chlorine atoms are called as organochlorine compounds.
Aldrin dieldrin, chlorobenzylate, DDT etc are some of the examples of chlorinated
hydrocarbons.
 Organophosphorous compounds (OP):
“Neutral esters or amid and thiol derivatives of phosphorous acids and carrying a
phosphoryl group (P-O) or thiophosphoryl (P-S) group are called as organophosphorous
compounds.”
Examples include malathion, parathion, chlorpyrifos etc.
 Carbamates:
Derivatives of carbamic acid that include sulfur containing sub groups of
dithiocarabamates and thiocarbamates are called as carbamates
Examples of carbamates include carbaryl, aldicarb and carbofuran etc

13. Con…..
 Pyrethroids:
Synthetic pesticides that have been designed based upon the structure of pyrethrins
(the six insecticidal constituents of natural insecticide pyrethrum).
Resmethrin, cypermethrin and allethrin etc are some of the examples of the
pyrethroids.
 Neonicotinoids
The class of chemical pesticides which comprises of nicotine mimicking chemicals
that targets the nicotinic acetylcholine receptors of central and peripheral nervous
system.
Acetamaprid and imidacloprid are important examples of neonicotinoids.

14. Classification of pesticides on the basis of
Targeted organisms
 Nematicides: (kills nematodes).Ethylene dibromode, dichloropropane, dibromo-chloroprapane etc
 Fungicides: (kills fungi.(Bordeaux mixture), Organometallic compounds of mercury and tin,
Chlorophenolics (e.g. trichlorophenol) , Synthetic organics (e.g. captans) .
 Herbicides: (kills weeds/ herbs).Some of the examples of herbicides include, alachlore, atrazine, 2,
4-D, glyphosate, arsenicals etc.
 Miticides/Acaricides: (kills mites)Organosulphurs and organotins etc.
 Rodenticides: (kills rodents).Alkaloid strychnine, hydroxycoumarin compound warfarin etc.
 Algaecides: (kills algae).Copper sulfate and dichlone are examples of algaecides.
 Insecticides: (kills insects). Arsenicals,fluorides,DDT, methoxychlor. Aldrin and dieldrin etc.

15. Classification of pesticide on the basis of
mode of action
 Broad spectrum/non selective:Examples include terbacil, oxamyl etc.
 Narrow spectrum pesticides: Chitin inhibitors and Juvenile Hormone Analogues etc.
 Contact poison: For example benzene hexachloride, carbamates, pyrethrum, rotenone
etc.
 Eradicant: Chemicals belonging to benzimidazoles and oxathlins etc.
 Protectant:Examples include dithiocarbamates, chloronitriles etc.
 Nerve poison: Organochlorine, carbamates and organophosphates are examples of
nerve poison.
 Systemic poison: Aldicarb, carbofuran. Mevinphos etc
 Repellent:permethrin, citronella oil, neem oil etc. are used as repellents.
 Stomach poison: DDT, Paris green, lead arsenate etc. are examples of the stomach
poison pesticides.
 Muscle poison: Ryania and sabadilla are examples of muscle poison.

16. Classification of pesticides on the basis of
method of entry into the body
 Stomach poisons:
For example dieldrin, sulfur, arsenate, lead etc.
 Contact poisons:
Examples are benzene hexachloride, carbamates, pyrethrum, rotenone etc.
 Systemic poisons:
Systemic poisons are aldicarb, carbofuran. Mevinphos etc.
 Fumigants:
Some of the examples are carbon tetrachloride, naphthalene and methyl bromide etc.