1. Insecticides, Herbicides and FungicidesBY
DR. GHULAM ABBAS

2. Insecticides An insecticide is a substance used to kill insects.
They include ovicides and larvicides used against insect eggs and larvae, respectively.
Insecticides are used in agriculture, medicine, industry and are considered major factor behind the increase in agricultural 20th century's productivity.
Nearly all insecticides have the potential to significantly alter ecosystems; many are toxic to humans; some concentrate along the food chain.
Insecticides can be classified in two major groups: systemic insecticides, which have residual or long term activity; and contact insecticides, which have no residual activity.

3. Systemic insecticides become incorporated and distributed systemically throughout the whole plant. When insects feed on the plant, they ingest the insecticide.
For instance, a gene that codes for a specific Bacillus thuringiensis biocidal protein was introduced into corn and other species. The plant manufactures the protein, which kills the insect when consumed.
Contact insecticides are toxic to insects upon direct contact. These can be inorganic insecticides include metals such as arsenates, copper including the commonly used sulfur. Contact insecticides can be organic insecticides, i.e. organic compounds, synthetically produced Or they can be natural compounds like pyrethrum (Chrysanthemum cinerariifolium and Chrysanthemum coccineum) , neem oil etc. Contact insecticides usually have no residual activity.

4. There are three distinguished types of insecticide.
1. Natural insecticides: It includes nicotine, pyrethrum and neem extracts, made by plants as defenses against insects.
2. Inorganic insecticides: which are metals.
3. Organic insecticides: which are organic chemical compounds, mostly working by contact.

5. History
Historians have traced the use of pesticides to the time 1000 B.C., but the earliest records of insecticides is the burning of "brimstone" (sulfur) as a fumigant.
Extracts of pepper and tobacco, soapy water, whitewash, vinegar, turpentine, fish oil, brine, lye were also used among many others.
At the beginning of World War II (1940), insecticide were limited to several arsenicals, petroleum oils, nicotine, pyrethrum, rotenone, sulfur, hydrogen cyanide gas, and cryolite.
It was World War II that opened the Modern Era of Chemical control with the introduction of a new concept of insect control --synthetic organic insecticides, the first of which was DDT (dichlorodiphenyltrichloroethane).

6. Classification of Insecticides
Organochlorines
The organochlorines are insecticides that contain carbon (thus organo-), hydrogen, and chlorine. The organochlorines are now primarily of historic interest, since few survive in today’s arsenal.
Diphenyl Aliphatics
The oldest group of the organochlorines is the diphenyl aliphatics, which included DDT, ethylan, chlorobenzilate, and methoxychlor. DDT  (dichlorodiphenyltrichloroethane) is probably the best known and most notorious chemical of the 20th century.
It is also fascinating, and the most useful insecticide developed. In 1973, when the U.S. Environmental Protection Agency canceled all uses.
DDT

7. DDT is still effectively used for malaria control in several third world countries. In 1948, Dr. Paul Muller, a Swiss entomologist (study insects), was awarded the Nobel Prize in Medicine for his lifesaving discovery of DDT (1939) as an insecticide useful in the control of malaria, yellow fever and many other insect-vectored diseases.
Mode of action The mode of action for DDT has never been clearly established, but in some complex manner it destroys the delicate balance of sodium and potassium ions within the axons of the neuron in a way that prevents normal transmission of nerve impulses, both in insects and mammals. It apparently acts on the sodium channel to cause "leakage" of sodium ions.

8. To cope with these problems, which it had itself created, the
World Health Organization was obliged to parachute into Borneo.

9. Hexchlorocyclohexane (HCH)
Also known as benzenehexachloride (BHC), the insecticidal properties of HCH were discovered in 1940 by French and British entomologists.
It has five isomers, only the gamma isomer has insecticidal properties. Consequently, the gamma isomer was isolated in manufacture and sold as the odorless insecticide.
In contrast, technical grade HCH has a strong musty odor and flavor, which can be imparted to treated crops and animal products. Because of its very low cost, HCH is still used in many developing countries.
Hexchlorocyclohexane

10. Mode of action The effects of HCH superficially resemble those of DDT, but occur much more rapidly, and result in a much higher rate of respiration in insects. The gamma isomer is a neurotoxicant whose effects are normally seen within hours as increased activity.

11. Organophosphates
Organophosphates (OPs) is the term that includes all insecticides containing phosphorus. All organophosphates are derived from one of the phosphorus acids, and as a class are generally the most toxic of all pesticides to vertebrates.
Mode of action The OPs work by inhibiting certain important enzymes of the nervous system, namely cholinesterase (ChE). This inhibition results in the accumulation of acetylcholine (ACh) at the neuron/neuron and neuron/muscle (neuromuscular) junctions or synapses, causing rapid twitching of voluntary muscles and finally paralysis.

12. Organosulfurs
These few materials have very low toxicity to insects and are used only as acaricides (miticides). They contain two phenyl rings, resembling DDT, with sulfur in place of carbon as the central atom. These include tetradifon (Tedion®), propargite (Omite®, Comite®), and ovex (Ovotran®).

13. Carbamates
The carbamate insecticides are derivatives of carbamic acid (as the OPs are derivatives of phosphoric acid). And like the OPs, their mode of action is that of inhibiting the vital enzyme cholinesterase (ChE).
The first successful carbamate insecticide, carbaryl (Sevin®), was introduced in 1956.
Two distinct qualities have made it the most popular carbamate: its very low mammalian oral and dermal toxicity and an exceptionally broad spectrum of insect control.
Other long-standing carbamate insecticides are methomyl (Lannate®), carbofuran (Furadan®) etc. Carbamates more recently introduced include primicarb, indoxacarb (registered in 2000).

14. Mode of action
Carbamates inhibit cholinesterase (ChE) as OPs do, and they behave in almost identical manner in biological systems, but with two main differences.
1- Some carbamates are potent inhibitors of aliesterase (miscellaneous aliphatic esterases whose exact functions are not known), and their selectivity is sometimes more pronounced against the ChE of different species.
2- Carbamates ChE inhibition is reversible.

15. PESTICIDES
Pesticides are preparations for the eradication of plant and animal pests, for the protection of plants, animals and man.
About 800 compounds of active ingredients of pesticides have been registered world-wide.

16. Pesticides Classified by Target
Term
Target
1. Algaecide
Algae
2. Avicide
Birds
3. Bactericide
Bacteria
4. Defoliant
Crop Foliage
4. Desiccant
Crop Plants
5. Fungicide
Fungi
6. Herbicide
Plants (weeds)
7. Insecticide
Insects
8. Miticide
Mites
9. Molluscicide
Molluscs
10. Nematicide
Nematodes
11. Plant Growth Reg.
12. Rodenticide
Rodents
13. Piscicide
Fish
14. Lampricide
Lamprey
15. Wood Preservative
Wood Destroying Pests

17. Mode of Action Examples
Broad Spectrum -- Kills broad range of pests, usually refers to insecticides, fungicides, and bactericides.
Contact Poison -- Kills by contacting pest.
Disinfectant (Eradicant) -- Effective against pathogen that has already infected the crop.
Germination Inhibitor -- Inhibits germination of weed seeds, fungus spores, bacterial spores.
Nonselective -- Kills broad range of pests and/or crop plants, usually used in reference to herbicides.
Nerve Poison -- Interferes with nervous system function.
Protectants -- Protects crop if applied before pathogens infect the crop.
Repellents -- Repels pest from crop or interferes with pest’s ability to locate crop.
Systemic -- Absorbed and translocated throughout the plant to provide protection
Stomach Poison -- Kills after ingestion by an animal.

18. Pesticide degradation
in abiotic environment (non-living)
the most important factors are light, temperature, photolysis, free radicals produced in photochemical reactions, hydrolysis
in biotic environment
1. phase phase
XH X – OH X – O – conjugate
The final products are inactive and are excreted.

19. Pesticides: Organochlorine pesticides Organophosphates
Carbamate pesticides
Pyrethroids
Phenoxyacetic acid – based pesticides
Urea – based pesticides
Diazine and triazine pesticides
Bipyridil – based pesticides
Phenylpyrazoles
Metal – based pesticides

20. Organophosphates - insecticides - antiparasitics
Mechanism of toxic action – irreversible inhibition of
enzymes, particularly of acetylcholinesterase on nerve
synapses (by phosphorylation of hydroxyl group of
serine bound in the active centre of ACHE).

21. Carbamate pesticides - insecticides - herbicides - fungicides
Mechanism of the toxic action – reversible inhibition of acetylcholinesterase (by carboxylation of hydroxyl group of serine bound in the active centre of ACHE).
Carbofuran is very up-to-date substance in toxicology. It is used to control vermin (foxes) and is used in baits. Birds are 10 times more sensitive to carbofuran than mammals (LD50 for mammals 3 – 19 mg/kg body weight). Frequent carbofuran poisoning cases among predatory birds.

22. Pyrethroids - insecticides - antiparasitics
Mechanism of the toxic action -
pyrethroids T (tremor) – contain no α-cyano group
cause reversible block of sodium channels (e.g. permethrin)
pyrethroids CS (choreoatetosis, salivation) – contain α-cyano group
cause reversible block of sodium channels and inhibition of GABA (e.g. deltamethrin)

23. Pyrethroids are - highly toxic for fish (LC50 below 0,1 mg/l) - toxic for bees (LD50 2 – 11 µg/bee) - not very toxic for mammals Cats are most sensitive mammals to pyrethroids. Why? - Pyrethroids’ detoxification, similarly to other organic toxicants, takes place in two phases. Activity of conjugation enzyme, especially of glucuronyl transferase, is very low in cats.

24. Urea – based pesticides - herbicides
They cause damage of the thyroid gland and diuron may cause methaemoglobinemia.
In mammals linuron reduces haematopoiesis
In dogs triasulfuron causes vacuolisation of liver cells, anaemia and accumulation of pigment in the liver

25. Diazine and triazine pesticides - herbicides
Diazine pesticides are less toxic than triazine ones
Mechanism of the toxic action –
atrazine damages the liver detoxication functions
simazine, prometryne, terbutryne – inhibit haematopoiesis
Toxicity: toxic for fish
relatively harmless for bees
LD50 for mammals exceeds 1000 mg.kg live weight

26. Metal – based pesticides
arsenic compounds – insecticides, rodenticides
phenylmercury – fungicide for treatment of seed (1913 – )
tributyltin – fungicide (xenoestrogenic effect)
thalium compounds – rodenticides
Today
Copper compounds – copper sulphate
- copper oxichloride
fungicides, algicides, molluscocides
Toxicity for fish – LC50 1 – 10 mg.l-1 depending on water quality

27. Fungi
Organisms that lack chlorophyll and obtain their food by living on other organisms
Reproduce by spores (aids in identification)
Attack crops above and below soil surface
Spread by wind, rain, insects, birds, soil, machinery and contaminated seed
Blue mold (apple) fungal spores and fruiting structures of cherry powdery mildew. Scanning electron micro-graphs by Alan Jones.

28. Types of Fungicides
Protective (preventative): application prevents the establishment of an infection
Curative: application interrupts the development of an established infection before visible symptoms
Eradicant: application interrupts further development of an established infection having visible symptoms
Residual: remains on surface of the leaf and provides protection
Systemic: movement of fungicide inside the plant (locally or throughout the plant).

29. Classes of Fungicides: Inorganics
Inorganics are protective (preventative) fungicides
Sulfur: one of oldest fungicides used, works as a general growth inhibitor; advantages include cheap cost and ease of application (dusts); disadvantages include limited spectrum of activity (best on mildews), must be applied frequently at a high rate and phytotoxic at high temperatures
Copper: phytotoxic to plants in elemental form (use uncommon)

30. Classes of Fungicides: Copper
Copper is bound to organic and inorganic molecules in fixed-type coppers, less toxic to plants
Broad spectrum poison; useful as fungicides and bactericides; protective (preventative) fungicides
Bordeaux mixture (copper sulfate and hydrated lime), copper sulfate, copper hydroxide and other copper compounds

31. Classes of Fungicides: Organics
Organics are protective (preventative) fungicides
Broad spectrum control, multi-site activity
Represent 60-70% of fungicides used
Dithiocarbamates: thiram
Ethylenebisdithiocarbamates (EBDCs): manozeb, maneb and zineb.
Captan: one of the most widely used fungicides worldwide, broad spectrum control
Chlorothalonil (Bravo, Daconil 2787): widely used, ornamentals and turf

32. Classes of Fungicides: Fumigants
Highly volatile chemicals that have fungicidal activity; include methyl bromide (controls fungi, nematodes, insects and weeds) and chloropicrin.

33. wildflowers
Tree
shrubs