Chemical control of plant diseases and public concerns

CHEMICAL CONTROL OF PLANT DISEASES AND PUBLIC

CONCERNS ABOUT THEIR USE.

Kamran Asif Khilji Roll Number : 04Advancements In Plant Pathology

Institute of Agricultural SciencesUniversity of Punjab, Lahore

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.

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

Before World War IIMetals 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

The Control of Other Pests

Bordeaux mixture (copper sulfate and

hydrated lime) First effective

fungicide, 1882 Pierre M. A.

Millardet, French National

Hero

Before World War IILead Arsenate Very

ImportantLead 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

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)

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)

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.

Paul MüllerNobel 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.

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

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

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. NeonicotinoidsThe 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.

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.

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.

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.