Читать книгу Herbicides and Plant Physiology - Andrew H. Cobb - Страница 37

Chemical weed control is a twentieth‐century technology. Copper sulphate was the first chemical used at the turn of the twentieth century to control charlock (S. arvensis) in oats, and soon after came corrosive fertilisers (such as calcium cyanamide) and industrial chemicals (including sodium chlorate and sulphuric acid). Modern synthetic herbicides first appeared in France in 1932 following the patenting of DNOC (4,6‐dinitro‐o‐cresol) for the selective control of annual weeds in cereals. Further dinitro‐cresols and dinitrophenols soon appeared, but these compounds had variable effectiveness and appeared to kill animals as well as plants. The discovery of the natural plant growth ‘hormone’ auxin in 1934 led to the further discovery of the synthetic growth regulators 2,4‐D and MCPA based on phenoxyacetic acid chemistry. These compounds were the first truly selective herbicides that could reliably kill broad‐leaved weeds in cereal crops, and they developed widespread popularity and use after the Second World War (Kirby, 1980). These compounds truly ‘replaced the hoe’ so that cereals could no longer be regarded as ‘fouling’ crops, and paved the way to the current practice of cereal monocultures.

Since the 1950s an increasing proportion of world cereal crops has become regularly treated with agrochemicals to achieve the control of an ever‐widening variety of weeds. Nowadays, chemical weed control has expanded to probably every crop situation in the world. Modern chemical weed control is not only more economical than traditional methods, but also has important technical advantages as weeds growing closest to the crop, and hence competing most for resources, can be controlled by selective herbicides. Furthermore, less crop‐root disturbance is evident than with mechanical hoeing and fewer, if any, weed seeds are brought to the surface in the process. Finally, farmers now have chemical answers for most weed problems at a reasonable price.