Pesticides and Pest Control

Pesticides are applied to the soil to manage the weeds. The length of the time that the pesticide remains active in soil is referred to as "soil persistence". Though desirable in the season of application, its persistence in the soils may affect the crop growth and yield. Benzene Hexachloride(BHC) is a chemical compound with several stereoisomers of which one is an insecticide called Lindane and the by-product is β-hexachlorocyclohexane- the pesticide. This pesticide which was used widely to protect cotton plants during 1960 and 1970's is banned as it has high levels of soil persistence and is neurotoxic for the animals. 

Pesticides have had some of their most striking effects on birds, particularly those in the higher trophic levels of food chains, such as bald eagles, hawks and owls. These birds are often rare, endangered and susceptible to pesticide residues, such as those occurring from the bioconcentration of organochlorine insecticides through terrestrial food chains. Pesticides may kill grain and plant-feeding birds and the elimination of many rare species of ducks and geese has been reported. Populations of insect-eating birds, such as partridges, grouse and pheasants have decreased due to the loss of their insect food in agricultural fields through the use of insecticides. Thus, the correct answer is option D.

In 1972, the 'Environmental Protection Agency' banned the use of DDT in the United States as well as the use of pesticides, such as endrin and dieldrin. As a result, the levels of these persistent compounds in the environment have decreased in most areas, thus, the reproductive success of brown pelicans has increased.

Phytophthora palmivora has been used as an post emergent mycoherbicide to control milkweed or strangler vine, a major problem on citrus in south Florida. It controls the weed by a root and stem rot and girdling the stems of infested plant near the soil surface, resulting in the death of seedlings and the older plants.

Agent orange was a powerful mixture of chemical defoliants used by U.S. military forces during the Vietnam war to eliminate forest cover for north Vietnamese, as well as crops that might be used to feed them. The U.S. program of defoliation, codenamed Operation Ranch Hand, sprayed more than 19 million gallons of herbicides over 4.5 million acres of land in Vietnam from 1961 to 1972.

Bacterial blight is a serious disease of field peas that is caused by the pathogens Pseudomonas syringae pv. pisi and Pseudomonas syringae pv. syringae. 

Aldrin is an organochlorine insecticide that was widely used until the 1970s, when it was banned in most countries. It is a colourless solid. Before the ban, it was heavily used as a pesticide to treat seed and soil. It is a chlorinated hydrocarbon. Thus, option C is correct. A carbamate is an organic compound derived from carbamic acid (NH2COOH). Thus, option D is wrong. Malathion is an organophosphate parasympathomimetic which binds irreversibly to cholinesterase. Malathion is an insecticide of relatively low human toxicity. It is not a chlorinated hydrocarbon. Thus, option A is wrong. Pyrethrum was a genus of several Old World plants now classified as Chrysanthemum or Tanacetum which are cultivated as ornamentals for their showy flower heads. Thus, option B is wrong. 

Organochlorine pesticides are highly lipophilic, meaning they are fat-soluble. This property allows them to accumulate in the fatty tissues of organisms and biomagnify through the food chain.

Malathion is an organophosphate parasympathomimetic, which binds irreversibly to cholinesterase. Malathion is an insecticide of relatively low human toxicity. Malathion is a parasympathomimetic organophosphate compound that is used as an insecticide for the treatment of head lice. It inhibits acetylcholinesterase activity of most eukaryotes. Malathion is toxic to aquatic organisms, but has a relatively low toxicity for birds and mammals. 

Herbicide carbamatets are asulam (thiocarbamate), carboxazole, chlorprocarb (phenyl carbamate), dichlormate, fenasulam, karbutilate, terbucarb.

The allethrins are a group of related synthetic compounds used in insecticides.

Atrazine, a triazine herbicide, is used in corn and sorghum for control of broadleaf weeds and grasses. Still used because of its low cost and because it works well on a broad spectrum of weeds common in the US corn belt, atrazine is commonly used with other herbicides to reduce the overall rate of atrazine and to lower the potential for groundwater contamination; it is a photosystem II inhibitor.

Insecticides based on their target sites and mode of action at the target sites can be classified into neurotoxins and others which do not target the nervous system of the insects. Insects have highly specialised interconnected cells nervous system along which electrical charge (impulse) travel. Neurotoxins target the enzymes involved in neurotransmission. The prolonged and irreversible disruption of a normal functioning nervous system may result in death.

Herbicides of photosystem-II inhibit the reduction of plastoquinone at the secondary quinone acceptor site and its subsequent re-oxidation. This consequently light induces charge separation which leads to recombination processes. This process generates reactive oxygen species causing extensive damage in PS II and eventually kills the plant.

Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colourless, tasteless, and an almost odourless crystalline chemical compound, an organochlorine, originally developed as an insecticide, and ultimately becoming infamous for its environmental impacts. Opposition to DDT was focused by the 1962 publication of Rachel Carson's book Silent Spring. It catalogued environmental impacts that coincided with the widespread use of DDT in agriculture in the United States, and it questioned the logic of broadcasting potentially dangerous chemicals into the environment leaving the residues for a long time.