Weeds and pests are the most important damages to agronomy system, which resulted in agriculture economic losses of more than $20.4 billion in 1972. Merely taking the United States as an example, the damage is $8.4 billion a year, while pests account for 40% and weeds account for 60%. In our country, China, the crop yield loss is almost fifty million kilogram per year.
Therefore, the prevention and management of weeds & pests are indispensable to guarantee the agricultural production. The common way to control them is spraying the chemicals termed herbicides and pesticides.
The first pesticide DDT appeared in 1939, which widely spread after the Second World War. People saw its tremendous potential through its high efficiency and lethality rate. Then synthetic organic pesticides quickly covered almost all fields where dedicates to controlling weeds and pests.
Resistance
At first, unprepared pest insects and weeds were easily killed, but this situation didn’t last long because of the resistance occurrence.
According to history, in 1989, there were 432 kinds of resistant insects in the world, and in 2008, the number updated to 589, of which 392 kinds were agricultural pests. What’s worse, beneficial insects, insect-eating birds, frogs and snakes are suffering as well from low selectivity chemicals.
As for wild grass, since the first one anti-2, 4-D wild carrots were found in the 1950s, weeds resistance problem has been always accompanying global agriculture development. Declared by Herbicide Resistance Committee( belongs to Weed Society Of America), as of May 21, 2014, resistant weeds occupied nearly 55% in total resistant organisms and they distributed among 65 countries, 82 kinds of crops.
Through figure 2, we can find that in the first 20 years, the occurrence of resistant weeds was very slow. But when getting into the mid and late-1980s, the number increased in a stunning speed and the growth rate shows a trend of nearly straitening up.
In the meantime, it is proved that these malignant weeds resist to 155 different herbicides and 22 of the 25 known herbicide acting spots became no effective. So they are too hard to manage.
Pollution
Today, more than 300 kinds of pesticides are commonly used in China. Their improper use has resulted in serious environmental problems.
In 1990, China's pesticides production was about seven hundred thousand tons. Only after 20 years, the output increased to 1.73 million tons with 13.4 kg/ha/year average dosage.
Unfortunately, 60%- 70% pesticides would be left in soil. It is proved that residual herbicide is harmful to crops by changing the soil PH, temperature etc, and this effect will last for at least 2 or 3 years. Some examples, The destructive herbicide sodium pentachlorophenol will cause potential phytotoxicity in a large area and result in crop failure. Gramoxone and 2,4-D etc these toxic pesticides, will easily volatilize and are able to drift over nearly 800 meters through spraying center, which could influence distant crops.
Poisoning
Because of bio-accumulation and being attached to the herbicide, human body becomes a heavy container of herbicide.
In Germany, the glyphosate content is 0.46-29.74μg/L in fourteen commonest beer which far exceeds the standard content 0.1μg/L.
Then it causes mucosal congestion, gene mutation and various inflammatory reactions. With the toxicant being absorbed into the blood circulation, it not only results in the mononuclear phagocyte, lymphocyte, and liver losing the function of defense and synthesis but also causes the pathological process of tissue diffusion, humoral diffusion even nerve diffusion.
International Agency for Research on Cancer (IARC) lists more than 10 kinds of pesticide such as glyphosate and sodium chlorate in “probably carcinogenic”. And epidemiological studies have found that glyphosateharborsm mutagenicity, genotoxicity, developmental toxicity, cytotoxicity and reproductive toxicity. It has been estimated that at least three million cases of pesticide poisoning occur worldwide each year, including 220,000 deaths which caused by long-term occupational exposure.
Lanzhou 2017
All serious situations above indicate that human is in need of a new cure for weeds and pests damage. For the sake of addressing this challenge, this year Lanzhou iGEM team aims at creating a novel Bio-pesticides which is harmless, eco-friendly and without resistance problem.
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