Next+to+Pesticides+Kill+Insects,+Weeds,+and+Fungi

=Pesticides Kill Insects, Weeds, and Fungi= ====A high-yield crop needs more than adequate nutrition, as well as a defense against natural enemies. To control these pests, farmers apply a substance known as pesticides. There are several kinds including insect-killing insecticides, weed-killing herbicides, and fungus-killing fungicides.====

__Insecticides Kill Insects__
====A small minority of insect species continually threaten our capability to grow, harvest, and store crops, and these are why insecticides are used. The most widely used insecticdes are chlorinated hydrocarbons, organophosphorus compounds, and carbamates. In 1939 there was a breakthrough in the fight against insect pests with the chemical synthesis of chroniated hydrocarbon DDT. During the 1940s and 1950s, DDT was applied to crops, resulting in markedly greater yields. Not only did DDT help protect plants, it protected people from mosquitoes, lice, and tsetse flies. It is estimated that DDT has helped save 25 million human lives.==== ====After a few years, insects developed a resistance to DDT. It was also found to be toxic to wildlife, including the natural predators of insects. Due to fewer natural predators, the DDT resistant insects began to thrive. in the 1950s and 1960s, other negative aspects of DDT and other pesticides were brought to the publics attention. In Rachel Carson's book //Silent Spring// she decribed a phenomenon known as **bioaccumulation,** where a toxic chemical that enters a food chain at low trophic levels becomes more concentrated in organisms higher up the chain. Due to this, DDT contributed to the decline of many bird populations and the near extinction of others.==== ====Many chlorinated hydrocarbon alternatives to DDT have been developed, like methoxychlor. This compound has a much lower toxicity, and unlike DDT is not stored in animal fat. DDT and methoxychlor are identical except methoxychlor has two ether groups and DDT has two chlorine atoms. Because they are nearly identical, they have nearly the same level of toxicity in insects.====



__Herbicides Kill Weeds__
====Weeds compete with crop plants for valuable nutrients. The traditional method for controlling weeds is to plow them under the soil, where in decomopsing they release the nutrients they absorbed while they were alive. Plowing //aerates// the soil, but it is either labor-intensive or energy-intensive and can lead to the topsoil erosion. In the early 1900s, farmers noted that certain fertilizers, such as calcium cyanamide, CaNCN, selectively kill weeds while causing little harm to crops.====

//Farmers in the United States apply almost 600 million pounds of herbicides annually, which is about three times more than the amount of insecticides they apply.//
====Two selective herbicides are the carboxylic acids 2, 4-D and 2,4,5-T. Both mimic the action of plant growth hormones and are selective in killing broad-leafed plants but not like grasslike crops such as corn and wheat. A herbicide known as Agent Orange is a blend of 2,4-D and 2,4,5-T. During Vietman, U.S. military forces applied more than 15 million gallons of Agent Orange and related herbicides in an effort to defoliate jungle areas that could harbor enemy troops.====



**__Fungicides Kill Fungi__**
====Fungi can play an important role in soil formation, but they can also harm crops. Most of the harm they cuase occurs during a plant's early growth stages. Fungi can also spoil stored food and are particularly devastation to the world's fruit harvest.====

====In the United States, farmers use about 100 million pounds of fungicides annually, meaning fungicides rank third after herbicides and insecticides in the amounts used. During the last 60 years, pesticides have benefited our society by preventing disease and increasing food production. Our need for pesticides will continue, but it will be greatly demanded.====



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