Everything you need to learn about controlling pests using insecticides.
Compounds of Insecticides:
[A] Inorganic Compounds:
(i) Paris green (double salt of copper arsenite and copper acetate) was firstly used as insecticide by about 1867 to control Colorado potato beetle.
(ii) Lead arsenate was used first in 1832 by Moulton to control gypsy moth in Massachusetts.
(iii) Calcium arsenate was first used by about 1906 to control leaf eating insects.
(iv) Sodium fluoaluminate (sodium aluminium fluoride) was used first in 1929 by Marcovitch and Stanely to control chewing insects.
(v) Lime sulphur was used first as a fungicide in 1852 by Grison and later in 1886 by Dusey to control San Jose Scale. Sulphur is primarily a fungicide and acaricide.
(vi) Borax (sodium tetraborate) is used to control fly maggot in manure pits and animal wounds infested by maggots.
(vii) Zinc phosphide (Zn3P2) is a well-known rat poison. Zinc phosphide when ingested into the rodent’s stomach, reacts with hydrochloric acid of stomach and releases phosphine gas which is extremely reactive and poisonous.
Other inorganics used as insecticides and pesticides are sodium fluoride, white arsenic, Barium carbonate, Thallium sulphate etc. Inorganics are stomach poison.
[B] Organic Compounds:
i. Hydrocarbon Oils:
Hydrocarbon Oils e.g., coal tar oil, mineral oil. Anthracnose oil is used for wood preservation. The phytotoxic nature of oils is due to presence of unstable unsaturated compounds. The mineral oils or the petroleum oils are derived from sedimentary rocks.
ii. Animal Origin Compounds:
The insecticide Nereistoxin is obtained from marine annelids Lumbrineris (Lumbriconeris) heteropoda and L. brevicirra.
iii. Plant Origin Compounds/Botanical Compounds:
(a) Nicotinoid/Nicotine:
Its main source is Tobacco. Nicotine shares 0.5 – 5.5% and 3.5 – 8.0% in the leaves of Nicotiana tabacum and N. rustica respectively. The scientific study of insecticidal property of Nicotine alkaloid present in tobacco leaves was made first time in 1828 by Passlet and Reimann. The structure of Nicotine was confirmed in 1893 : 1-3 (1-methyl -2- Pyrrolidyl) pyridine.
Nicotine is a contact and nerve poison which affects especially soft bodied insects. Its main effect is on aphids and thus prior to the use of synthetic insecticides it was known as aphicide. It has no phyto-toxic and residuary effect, that’s why the sprayed crops may be harvested just after two days. But for the mammals, it is highly toxic. It is marketed in the name of Nicotine sulphate. Due to high volatization rate, it may be used as fumigation in the glasshouse. Dust formulation of nicotine sulphate releases nicotine in the presence of moisture.
(b) Pyrethroids/Pyrethrins/Pyrethrum:
Source:
White flowers of Chrysanthemum cinerariefolium (Guldaodi). In the beginning of the 19th centuary (1800-1899) Jumtikoff of Armenia found that the tribals of the Caucasus (the area between the Caspian Sea and black sea) were using the flower dust of chrysanthemum spp. Generally the mixed esters of Pyrethrolone and Cinerolone are called pyrethroids/Pyrethrins in which 0.7 to 3% is chrysanthemic and Pyrethric acids. Since these esters can’t be separated, therefore it is collectively called Pyrethrins.
Pyrethrins are powerful contact insecticides which rapidly paralysed the housefly. This characteristic action is known as “knock down” effect. It is extremely unstable hence it is of little value for field crops. Pyrethrum is used with the solvent of DDT e.g. Flint. Here DDT acts like synergist which increases the action of pyrethrins. The equivalent synthesized compounds of pyrethrins are Allethrin, Cypermethrin, Dimethrin and Barthrin which are harmless to man.
(c) Rotenoids/Rotenone:
Source:
Roots of leguminous plants Lonchocarpus spp (South American plant) and Derris eliptica (Malaysia). Insects poisoned with rotenone show a steady decline in oxygen consumption followed by paralysis and death. It is well known contact fish poison. It was first used in 1848 against leaf eating caterpillars. However rotenone was first isolated in 1895 by Geoffrey. It is used as dust containing 0.75 – 1.5% rotenone and effective against beetle and caterpillars.
(d) Raynia/Ryanodine:
It is an alkaloid derived from ground roots and woody stems of South American shrub. Ryania spaciosa (family-Flacourtaceae). It is a stomach and contact poison and effective against Lepidopterous pests. It is a muscular poison and known for blocking the conversion of ADP to ATP in striated muscles. It is used as dust (20-40%).
(e) Sabadilla:
It is an alkaloid derived from seeds of tropical lily Schoenocaulon officinale (Family: Liliaceae) found in South and Central America. The alkaloids mainly cevadine and veratridine are contact poison and used for the control of houseflies and domestic insects. It is harmful to pollinators honeybees.
(f) Margosa (Neem)/Azadirachta indica:
Kernels of the neem tree (Azadirachta indica) possess extraordinary gustatory repellant properties which are attributed to the active ingredients nimbidin-T, meliantriol and azadirachtin. The main a.i. azadirachtin is present in seeds and leaves and varies from 2-4 mg/g Kernel. Neem is known for various insecticidal properties e.g., antifeedant action, insect growth regulatory activity inhibits juvenile harmone synthesis, Oviposition deterrent, repellant action, reduction of life span of adultsand intermediates.
Insecticide vapacide is prepared from neem cake. The commercial neem insecticides available in market are based on neem seed kernel extract (NSKE). Some products are Gronim, Neemazal, Achook, Nimbecedine. Neem based products are sensitive to UV light i.e. it degrades when exposed to sunlight.
Some another botanicals are yet to be used on large scale:
(g) Limonene and Linanool are citrus peel extracts which cause insect paralysis. They evaporates quickly in environment hence are used to control aphids, mites and fleas.
(h) Garlic oil due to presence of diallyl disulfide and diallyl trisulfide shows larvicidal property and is fatal to larvae of mosquito Culex pipiens quinquefasciatus.
(i) Root diffusates of the crucifers Brassica nigra and Sinapis alba inhibit emergence of the golden cyst nematode of potato (Globodera rostochiens) due to the presence of isothiocyanates. Thiophenic compounds present in Tagetes sp. suppress the population of Meloidogyne, Prafylenchus penetrans etc. Root extracts of Asparagus racemosus inhibits hatching of eggs of Meloidogyne jauanica and M. arenaria. Tannin and polyphenols found in aqueous extracts of raspberry roots and canes (Rubus ideaus) are poisonous to the nematode Longidorus elongatus.
Synthetic Organic Compounds:
Such organic compounds may be broadly grouped into Organochlorines, organo-phosphorus compounds, Carbamates Dinitrophenols.
[A] Chlorinated Hydrocarbons:
(1) DDT- C14H9Cl5
DDT → Dichloro Diphenyl Trichloroethane but chemical name of DDT is-
p 2-bis (p-chlorophenyl) 1,1,1 – trichloroethane (old).
2, 2—bis (p-chlorophenyl)-l,l trichloroethane (new).
DDT is a mixture of two isomers viz., pp’-DDT (>80%) and op’-DDT. DDT was first synthesized by Othmar Ziedler in 1874 but its insecticidal property was first discovered by Paul Herman Mutter of Ciba Giegy Company in 1939. Muller obtained Swiss patent in 1942 for his discovery and awarded Nobel Prize in Medicine in 1942. This Insecticide was used on the large scale first time during World War II in 1942 by the Allied Troops in Naples, Italy. It was discovered as first protective insecticide.
It is a stomach and contact poison. It is one of the most a polar compounds and practically insoluble in water, pp’ – DDT is more toxic than op’ – DDT. DDT poisoned insects show tremors throughout the body and the appendages, characteristically called “DDT Jitters”. Its use in agricultural sector has been withdrawn in India and permitted to be used only for mosquito control under public health programme as 50% WP or 75% WP.
DDT Analogs:
i. Rhothane (trade name) is a contact & stomach poison.
ii. Methoxychlor is easily biodegradable and has faster knock down of houseflies.
iii. Dicofol (Kelthane) is effective as acaricide and used presently for control of mites. It is effective for all stages of mites, harmless of bees and possesses long residual effect. Its acaricidal properties were first discovered by -J.S. Barker and F.B. Maugham in 1956.
iv. Acaricides like DMC (Dimite) and Chlorobenzilate are another DDT analogs.
BHC/HCH:
Benzene Hexachloride/666/Gammexane.
Benzene Hexachloro Cyclohexane.
C6H6Cl6 – 1, 2, 3, 4, 5, 6 -hexachlorocyclohexane (i.e. HCH). The HCH compound was first synthesized in 1825 by Michael Faraday but its insecticidal properties were rediscovered between 1940-1942. HCH has 6-isomers but γ-isomer (Gamma-BHC) is highly active for insecticidal property.
The composition of isomers in BHC:
(i) Alpha (α) – 55-70%
(ii) Beta (β) – 5-14%
(iii) Gamma (γ) – 10-18%
(iv) Delta (δ) – 6% – 7%
(v) Epsilon – 3-4%
(vi) Eta – in trace
A German chemist Van der Linden discovered four isomers of BHC in 1912. The toxic γ-isomer was isolated by British group of scientists and named it Lindane (Gammexane) in honour of van der Linden. Toxicity of BHC is proportional to the toxic content of γ-isomer. The prepared product Lindane contains at least i.e., a minimum of 99% γ-isomers. It is a stomach and contact poison and has fumigant action.
Since Lindane dechlorinates in normal alkali condition, therefore it is not used in alkali soil. It should not be sprayed on vegetable, roots, tuber crops and fruits otherwise it may have harmful effect. However it is not harmful for the crops but may damage the primary growth stage of cucurbits. There must be a gap of two weeks between harvesting and spraying on crops. It is used to control soil insects and ectoparasites and it has long residue in the soil.
Cyclodiene Insecticides:
Such are highly chlorinated cyclic hydrocarbons having ‘endomethylene bridged’ structure. The toxicity of these insecticides is due to its high lipoid solubility such insecticides are:
a. Chlordane C10H6CI3:
Its insecticidal property was described firstly in 1945 by Kearns et al. It is a presitent (stomch + contact) poison and light fumigant. It is especially effective against soil insects and termites. It should not be used on leafy vegetables. It becomes non-poisonous due to alkaline dehydro- chlorination. That’s why it is not kept in Zinc containers or galvanized containers. Its use in India is withdrawn.
b. Heptachlor C10H5CI7:
It was introduced in 1948. It is (contact + stomach) poison and has some fumigant property also. It is 4-5 times more effective than chlordane. It may be used for seed treatment and soil treatment. It has no residual effect. It has no harmful effect on leafy vegetables. Therefore it is used on agricultural and horticultural plants. It is generally compatible for all insecticides and fungicides. But nowadays its use in India has been withdrawn.
c. Aldrin- C12H8Cl6:
The insecticidal properties were firstly described by C.W. Kearns et. al. in 1949. It is named after the German chemist Kurt Alder who received the Nobel prize in chemistry in 1950 for his work on diene synthesis used in formulation of cyclodiene insecticides. It is a persistent stomach + contact poison which is used against soil insects.
The epoxidised conversion of Aldrin into Dieldrin (C12H8Cl6O) in soil is highly persistent but Aldrin itself is not persistent. Therefore it has limited use. In alkali soils Aldrin is used instead of y-BHC or lindane. Its use is also withdrawn in India. In India Dieldrin is only used for locust control. Endrin is banned in India which is an isomer of Dieldrin.
d. Endosulfan (Thiodan)- C9H6Cl6O3S:
It is an insecticide of Sulphite group. The insecticidal properties were firstly described by W. Finkenbrink in 1956. It is a contact + stomach insecticide and has slight fumigant action. It is practically soluble in water, persistent and non-volatile. It is used in the form of spray and its general formulation is 35% EC. Due to high toxicity, the sprayed crop may be harvested after at least six weeks gap. Due to its harmful effect, the state govt. of Keral banned it in July 2002.
[B] Organo-Phosphorus Compounds:
The insecticidal properties of Organo-phosphates were firstly discovered by Gerhard Schrader (chemist) in 1939. He found that some poisonous compounds were absorbed through the plant leaves or roots and were diffused into the whole parts and thus the plant escaped from the insect attack due to poisoned sap. The one such compound was Octamethyl Pyrophosphoramide (OMPA/Schradan). Schrader developed Tetraethyl pyrophosphate (TEPP) as a substitute for nicotine. The insecticide detoxified into the plant due to enzymes of plant.
Cholinesterase, an enzyme, is an essential constituent of the nervous system in both insects and higher animals. The Organo-phosphate phosphorylate the active site of this enzyme and such phosphorylated enzyme is an irreversible inhibitor which inhibits the normal process of quick removal and destruction of neurohormone acetylcholine (Ach) from nerve impulse resulting into the accumulation of acetylcholine and therefore the normal process of Nervous system is disrupted. Such Organophosphate as a nerve poison was firstly synthesized during the First World War.
Before the spraying of any systemic organophosphate one should verify the sufficient moisture into the soil. The deficiency of soil moisture causes the accumulation of active ingredient (a.i.) on the leaf margin which may result into margin burn or Necrosis. Most of the Chlorinated insecticides can be stored for a longer period but Organo-phosphate for the shorter period.
Organophosphate has certain advantages such as rapid action against a wide spectrum of pests, low persistence, breakdown to form products non-toxic to man & animals, low dosages required per unit area, comparatively low mammalian toxicity and relatively thick metabolism in vertebrates and absence of accumulation in their bodies. Organo-phosphates are successful insecticides.
a. Phosphomidon (Dimecron):
It is a systemic insecticide since it is highly soluble in water, it is suitable for low volume and Ultra low volume spray (LVS/ULVS). In alkaline medium, its insecticidal property is reduced due to rapid hydrolysis. Therefore it is not sprayed along with such fungicides like Bordeaux mixture, Lime Sulphur, Nicotine Sulphate and Copper Oxychloride. It was first synthesized in 1955 by E. Beriger of CIBA but its insecticidal properties were described in 1956 by F. Bachmann and J. Meierhans. It is used to control sucking pests, leaf miners, certain mites etc.
b. Dichlorovos (DDVP/Nuvan):
It is contact + Systemic poison and slow fumigant also. It brings about quick knock down effect. Its insecticidal properties were described. First in 1951 by CIBA. It does not leave any residue on plant and therefore it may be used on all crops until shortly before harvest. Soon after sprayed on leaves, it starts hydrolyzing into harmless dimethyl phosphoric acid and dichloroacetaldehyde which thereafter decomposes and evaporates. It is used to control household pests, lepidopterous larvae, sucking pests etc.
c. Trichlorfon:
This product was prepared by W. Lorenz but was introduced by Bayer in 1952. It is a contact and stomach insecticide with some fumigant action. In an alkaline medium of above PH-6, it is dehydrochlorinated and the principal product of this reaction is dichlorvos. In insects its toxic activity is attributed to metabolic conversion to dichlorvos. It is quick acting and effective against lepidopterous and dipterous pests and sucking insects. Registered formulation are 5% DR 50% EC and 5% Gr.
d. Phosdrin (Mevinphos):
For a short period, it is a good insecticide to control sucking and chewing insects. But it is rapidly hydrolysed in alkaline medium.
e. Monocrotophos (Nuvacron/Corophos):
It is highly effective organophosphate insecticide which has systemic and contact action. It is acaricide also. It is effective against thrips, leafminers, chewing and sucking pests. It is harmless on the normal recommended dosage. It should not be mixed with the alkaline pesticides.
f. Parathion (Thiophos):
Its insecticidal properties were first described by Schrader in 1944. It is known for contact action whose effect is rapid. It may be used as nematicide. It is not suitable for alkaline medium.
g. Methyl Parathion:
The toxicity of Methyl Parathion is comparatively very less to mammals but highly toxic to insects. Therefore its use is comparatively more. It is used to control a wide range of pest. Registered formulation is 2% DP and 50% EC.
h. Malathion:
It was introduced in 1950. Its toxicity for mammals is very low e.g. acute oral LD50 for rat is 2800 mg/kg. It is corrosive to iron and on prolonged contact with it loses its insecticidal activity. It is incompatible with alkaline pesticides. It is a non-systemic and used to control a wide variety of pests especially in fruits, vegetables and stored grain pests and external parasites of livestock. It is harmless for almost all corps except ornamental plants. Its technical product is 95% pure. Although its low mammalian toxicity, there should be a gap of at least 4 days between the spraying the crop and its harvesting.
i. Diazinon:
It was introduced in 1952 but its insecticidal properties were described in 1953 by R. Gasser. It is a contact & stomach poison with fumigant action and penetrating effect. It has nematicidal effect also. It is used to control aphids, thrips, mites and houseflies. It controls soil insects successfully. It should not be mixed with Copper fungicides. It is harmless for crops but it may harm to tomato and cucumbers at low temp.
j. Dimethoate (Rogor):
It was described in 1956. It is a systemic and contact insecticide and acaricide. It is used to control a wide variety of sucking pests & lice infesting poultry. It loses its insecticidal properties in alkaline medium. The crop should be irrigated before spraying it. It is formulated as 30% EC.
k. Thimet (Phorate):
It is a systemic insecticide and mainly used for soil treatment to protect the crops at the sowing time. It has contact and fumigant action and to some extent nematicidal and acaricidal action also. It does not persist for a longer period. It is also effective against sorghum shootfly and rice gallfly. It is formulated as 10% a.i. granules. It protects the crop for 20-25 days.
l. Metasystox (Methyl demeton):
It is comparatively more effective than systox (Demeton). It is a systemic insecticide and effective against sucking pests. Its formulation is 25% EC.
m. Chlorfenvinphos:
Its insecticidal properties were described in 1962 by W.F. Chamberlain et. al. It is contact insecticide effective against pests resistant to organochlorines. It is used to control root flies, cutworms etc. as a soil insecticide. @ 2 – 4 kg a.i./ha and on foliage stem borers, leaf hoppers, leaf beetles etc. It’s registered formulation in India is 10% granules (Gr.)
n. Chlorpyrifos:
Keraga et. al described its insecticidal properties in 1965. It is effective against sucking and chewing pests and household pests particularly in mosquito larval control @ 0.5 kg a.i./ha. It is rapidly detoxified in the animal body. Registered formulations are 20% EC, 10% Gr & 1.5% DR
o. Phosalone/Zolone:
It is a non-systematic contact insecticide and acaricide effective against a wide spectrum of pest spp., particularly of cotton. It is safe to bees and natural enemies of pest spp. Formulation is 4% dust & 35% EC.
p. Quinalphos:
Its insecticidal properties were discovered in 1969 by Schmidt & Hammann. It is an insecticide and acaricide with contact and stomach action. It is used to control sucking insects and lepidopterous larvae particularly of cotton and rice. Formulation is 25% EC, 5% granule & 1.5% dust.
q. Triazophos:
It is a broad spectrum insecticide/acaricide with contact & stomach action and effective against lepidopterous larvae etc. on cotton, vegetables etc. Registered formulation are 20% EC & 40% EC.
r. Propetamphos:
It is a contact & stomach insecticide with long residual activity. It is effective against household and public health pests especially cockroaches, flies, fleas, mosquitoes, clothes moth, ants and animals ectoparasites such as lice, ticks & mites. Registered formulations are 20% EC & 1% spray.
‘S’- Containing Insecticides:
(a) Metasystox
(b) Rogor (Dimethoate)
(c) Malathion
(d) Parathion (Thiophos)
(e) Methyl Parathion
(f) Dimeton (systox)
(g) Propetamphos
(h) Fenitrothion
(i) Diazinon
(j) Coumaphos
(k) Phorate
(l) Endosulfan
(m) Chlorpyrifos
(n) Phosalone
(o) Quinalphos, and
(p) Triazophos.
Carbamate Insecticides:
Carbamate compounds are derivatives of Carbamic acid and dithiocarbamic acid. Organophosphates are highly effective against a wide spectrum of insect-pests due to their capacity for inhibiting cholinesterase in insect nerve tissue. In the same way some Carbamates (e.g., aryl esters of N-methyl carbamic acid) show insecticidal properties becoming competitive inhibitors of cholinesterase. The insecticidal properties of carbamates are attributed to their structural resemblance to acetylcholine and thus have a high affinity for the particular enzyme cholinesterase.
a. Carbaryl (Sevin):
H.L. Haynes et. al first time pointed out its insecticidal properties and was introduced in 1956. It is a contact insecticide with slight systemic action. It is comparatively safer for human and mammals than chlorinated and Organophosphates. It is effective against a wide spectrum of insects pests of crops particularly cotton but ineffective against mites. It should not be mixed with alkaline compounds. It is formulated as 5% or 10% dust, 4% granules & 50% WP or 85% SP or 40% LV Sevidol (granules) = 4% Carbaryl + 4% γ-HCH used to control rice pests.
Sevimol 40LV – 40% Carbaryl + Molasses.
b. Carbofuran (Furadan):
It is a systemic insecticide and nematicide effective against sucking and soil inhabiting pests. It is used to control sorghum shootfly. It is unstable in alkaline medium its application stimulates growth in cotton, rice, tobacco, sorghum and corn. It is formulated as 50% SP and 3% granule.
c. Carbosulfan:
It is effective against a broad spectrum of pest species on various crops. It is metabolized in plants to carbofuran and 3-hydroxycarbofuran.
d. Aldicarb (Temik):
It is a systemic insecticide, acaricide and nematicide and highly poisonous for mammal. Its insecticidal properties were described by M.H.J. Weiden et. al. and was introduced in 1965.
e. Methomyl:
It is effective against sucking insects and mites and lepidopterous larvae especially cabbage looper and diamond back moth. It also controls nematodes.
Synthetic Pyrethroids:
The First synthetic analogue of pyrethrum was Allethrin which was firstly developed by Green & La Forge in 1949. Since then so many synthetic pyrethroids have been developed.
a. Allethrin:
It is known for quick knock down effect on flies and mosquitoes when applied with synergists like piperonyl bitoxide.
b. Cypermethrin:
It was discovered by M. Eliott et. al in 1975. It is a stomach and contact insecticide effective against various lepidopterous larvae particularly boll worms & leaf eating caterpillars of cotton. Formulations are 10% EC & 25% EC.
c. Etofenprox:
It is non-ester pyrethroid introduced in 1987. It is a contact stomach insecticide. It is effective against Rice leaf hoppers and brown plant hopper (BPH). It is also effective against cockroaches and houseflies. Its Formulation is 10% EC.
Acaricides:
Such chemical controls or kills the acarina (mites) is called acaricide. Aramite is the ideal acaricide which controls mites. It is harmless for predators, human and animals. DINOCAP is an another acaricide and contact fungicide and was firstly introduced in 1946 by Rohm and Hass company. Trade name of DINOCAP is Karathane. The registered formulation of DINOCAP is 48% EC. Other acaricides are- Azobenzene, Dicofol, chlorobenzilate, Chlorafenson, Fenson, Tetradifon, chlorben, side, abamectin, Flufeboxuron.
General Dose:
Systemic Pesticides @ 0.02 – 0.05% a.i. for spray.
Contact pesticides @ 0.05 – 0.07% or even 1.0% a.i. for spray.
Granular systemic insecticides @l-2 kg a.i./ha for soil application.
Fungicides @ upto 2 g/l depending upon chemical used, pest species and season of application.
Fumigants:
Fumigants are such pesticides which have the capacity to kill the particular pest by converting into gaseous state at the required temp, and pressure. It is also called gaseous poison. Such gas enters into the larvae, pupae and adults of insects through spiracles and the eggs through the chorion during respiration and thus brings about death.
Fumigant may kill all types of insects because it has no significance of mouth parts and feeding habit of insects. Such fumigant which vapourizes readily at the room temp, is the most useful. The essential feature of soil fumigant is that the released vapour must be slowly.
Fumigation is required to kill or control a great variety of pests of stored products, household articles, soil inhabiting insects & nematodes as well as for a quarantine measures at the time of export-import.
The following prevalent fumigants are:
(i) HCN (Hydro-Cyanic Acid or Hydrogen Cyanide):
It is most extensively used fumigant and was firstly used to control cottony cushion scale Icerya perchasi in 1886 by D.W. Coquillett. HCN is obtained from treating the sodium with sulphuric acid.
(ii) Bromo-Methane/Methyl Bromide:
It is 1.5 times heavier gas than air, therefore its penetration power is remarkable. In 1932, its insecticidal properties were described by Le Goupil. It is used to control soil insects, nematodes, soil weeds and fungi and rodents.
(iii) Chloropicrin (Trichloro-Nitromethane):
It is a tear gas. Its use is not registered in India.
(iv) Ethylene Dibromide (EDB):
Its insecticidal properties were described by Neifert et. al. in 1925. It is used for fumigating fresh fruits and vegetables to control fruitfly larvae because it does not affect plant materials. It is also used to control nematodes (except cyst nematodes Heterodera spp. and soil fungi).
(v) Phosphine (PH3)/Hydrogen Phosphide:
It is widely used in fumigating grains, flour and cereals in godowns.
PH3 is liberated from Aluminium phosphide in presence of moisture:
AIP + 3H2O → PH3↑ + Al (OH)3
But it is available in the market in the pellet forms. The combination of pellet is 55% Aluminum phosphide, 40% ammonium carbamate and 5% aluminium oxide. PH3 is highly toxic to all stages of insects and rats. The pellet containing ammonium carbamate releases CO2 and ammonia (NH3) which prevent spontaneous ignition of phosphine gas. And the final product formed is aluminium hydroxide which is harmless. A pellet (Tablet) weighing about 3 kg liberates 1 kg PH3 approximately.
Celphos is the such tablet.
Other fumigants are Nicotine, carbon disulphide (CS2) Dichloropropene, vapam, Napthalene etc.
Rodenticides:
Generally two types of poison are used to kill rats/rodents:
(a) Acute Poison:
It includes:
(i) Antu.
(ii) Barium Carbonate.
(iii) Zinc Phosphide.
(iv) Thallium Sulphate.
(v) Arsenic Compound Pre-baiting is required for all the poisons.
(b) Chronic/Multidose Poison:
Such poisons are anticoagulants which are derivatives of hydroxy-coumarin. Anticoagulant is the name of that compound which prevents the blood clotting. The prevalent examples are-warfarin (tomorin/ Coumachlor), Diphacinone, Coumafuryl, Coumatetralyl, Bromadiolone.
To control the mole rats (which live in the burrow), Aluminium phosphide (PH3↑) is used.
The maximum use of pesticides in India is on cotton (more than 50% of the total pesticides used) 2nd on cereals and 3rd on Fruits & vegetables. The Insecticide accounts for 80% of the total pesticides.
The enzymes present in the plant is responsible for the detoxification of pesticides in the plant body.
Formulation of Insecticides:
Only a small quantity of the poison or toxicant is required to control the pest. Such a small quantity is difficult to apply in an effective manner. Therefore the toxicant is required to be formulated. The volume of the toxicant is increased by adding inert materials to the pure and technical form of Poison. The inert material is called Additive and the process to get mixture by adding inert materials to the pure and technical form is known as Formulation.
The common formulations are:
(i) Dust Additives:
Toxicant + Carriers/Extenders/Diluents/Vehicles. Particle’s size is the determining factor to choose the carrier.
Dust Carrier:
(a) Organic Compounds e.g. Flour of Walnut, Soybean, Shell, & Woodbark.
(b) Inorganic compounds e.g., pulverized mineral (sulphur, diatomite (Silicon oxide) tripolite, lime, gypsum, talc, pyrophyllito or clay (attapulgite, benetonites, kaolins, volcanic ash).
(ii) Spray Addititives:
(a) Solvent:
Kerosene Oil, diesel of petroleum, xylene etc., are used as solvents.
(b) Wetting Agents:
It is required to convert a water insoluble toxicant into a soluble or partly soluble one.
(c) Emulsifier:
It is required to prevent a solvent dissolved toxicant from precipitating out. e.g., sodium oleate, amines, sodium lauryl sulphate etc.
Commercially many pesticides are sold in the market as an Emulsifiable concentrate (EC).
EC = toxicant + solvent + Emulsifier + Water + water means the recommended amount of water which is required to add at the time of use.
(d) Spreader/Deflocculator:
Such additives are required to improve wetting through spreading property e.g. Calcium caseinate, Soybean flour, sulphated alcohols or sulphonated compounds etc.
(e) Sticker:
It prevents the pesticide from washing off by rain or dew e.g. gelatin, resin, glue, starch, vegetable oil etc.
(f) Stabiliser:
Such additives are required to retard rapid decomposition of unstable organic pesticides e.g. isopropyl cresols, hexamethylene tetramine & epichlorohydrin prevent the decomposition of pyrethrins, endrin and aldrin respectively.
(g) Softener:
It reduces the phytotoxicity of pesticide e.g. sulphur, zinc sulphate, lime casein etc.
(h) Masker or Deodorant:
It suppresses (masks) the unpleasant odours when used for household purposes e.g. cedar oil, pine oil, scents etc.
Types of Formulation:
I. Solid Formulation:
(i) Dust:
Such mixture which is obtained by mixing toxicant with the dust carrier, is called dust. Dust is the general term of the particle having the size less than 100 micron (µ.).
Finished Product = toxicant 0.1-25% + carrier 99.9-75%
The amount of toxicant ranges from 0.1% to 25% and the rests in the dust formulation are carriers.
Lesser the particle size, higher the toxicity. Particle size of the Dust formulation = 1 – 40µ
(ii) Granules:
Toxicant- 2 – 10%
Particle size- 0.25 – 2.5 mm diameter but usually 250µ – 1250µ i.e., 0.25 mm – 1.25 mm
Those having particle size 100µ – 300µ are called microgranules and those above 300µ are known as granules.
Microgranules- 100µ – 300µ
Granules- > 300µ
(iii) Insecticide – Fertilizer mixture is also prepared to control the soil insect.
II. Liquid Formulation/Spray:
(i) Concentrate liquid or Undiluted Liquid:
The Highly concentrated liquid of technical grade of the toxicant is dissolved in non-volatile and non-phytotoxic solvents. To enable solution and drop formation a volatile solvent is also added but emulsifier is not added. The concentrate liquid formulations of Malathion & Fenitrothion are used in ultra-low-volume (ULV) quantities.
(ii) Solution Concentrate (SC)/Solution:
Such pesticides are formulated in a single liquid phase either in water or in an oil.
In Water:
Monocrotophos, Organophosphates
In Oil:
Flint type domestic spray.
(iii) Emulsifiable concentrate (EC):
Such formulation contains the toxicant, a solvent. For the toxicant and an emulsifying agent i.e., emulsifier-
E.C. = toxicant + solvent + Emulsifier
It may be of two types:
(a) Oil in water type.
(b) Water in oil types.
Reasons to add emulsifier are:
(a) To dilute water insoluble chemical (with water).
(b) To spread and wet the treated surface by reducing the surface tension of the spray.
(c) To stabilize the emulsion.
(d) A better contact is possible with insect cuticle.
(iv) Suspension:
In such formulations, active materials are suspended as solid particles in water.
Such formulation is required when an active ingredient is insoluble in either water or organic solvents. Such formulation is called suspension or Flowable (F) or suspension concentrate.
(v) Foam:
Foam producing nozzle converts the pesticide spray into foam.
(vi) Mist:
Very small droplets are called mist.
Droplet size- 50 – 150µ (micron)
[1µ = 10-6µ]
Droplet size means the median diameter of the droplet.
(vii) Fog:
Its droplet size is more-lesser than mist:
Droplet size- 1 – 50µ
[Particle size of smoke- 0.001 – 0.1µ]
(viii) Aerosols:
When minute droplets or particles are suspended in the air like mist or fog, are called aerosols i.e., aerial solution.
Droplet or particle size- 0.1 – 50µ
A more popular form of aerosol formulation is aerosol bomb which is used in household or camps to kill mosquitoes.
(ix) Water Dispersible Powder/Weltable Powder: (WDP/WP):
W.R is the powder formulation which yields rather stable suspension when diluted with water. Water insoluble toxicant is mixed with carrier. Carrier is partly soluble in water and is capable of making a fine suspension in water and thus such mixture is called WDP. The active ingredient in W.P./WDP ranges 15-95% but commonly a.i. is 25-50%.
The concentration of toxicant is comparatively more than that of Dust.
(x) Water Soluble Powder (WSP/SP):
WSP is a powder formulation readily soluble in water. It usually contains a high conc. of active ingredient and therefore easy to store and transport, e.g. Carbaryl 85 SP and Acephate 75 SR
III. Gaseous Formulation:
It is also called fumigants.
Particle size of smoke, 0.001 – 0.1µ.
Classification of Spray Volumes:
(a) High Volume Spray (HVS):
Here spray liquid is used more than 400 l/ha.
=> 400 l/ha of spray liquid used
(b) Low Volume Spray (LVS):
5 – 400//ha of spray liquid.
For aerial dose- 15 – 75 l/ha
Ground dose- 100 – 200 l/ha
(c) Ultra-Low Volume Sprays (ULV) or Low volume Concentration Spray (LVC):
ULV/LVC- < 5 l/ha of spray liquid used.
Here quantity of formulation is less than 5 l/ha and more concentrated formulation is used without diluting with water. To compensate the low (Small) volume, it is required to break down the concentrate into extremely fine particles. In India ULV is sprayed by the aircraft e.g. Malathion conc. (95% a.i.). In our country, due to lack of proper equipments, the ULV spray is generally used in aerial spray. Aerial spraying is done by both by fixed-wing aircrafts and helicopters. For ground spraying, Aspee’s modified mist blower and Knapsack are used.