Weeds are undesirable plants growing within a crop. They compete for resources such as nutrients, water and light. Without weed control, crop yields can be significantly reduced (40-100%) depending on the competitiveness of the crop, composition of the weed flora and level of weed infestation. Weeds can also cause further problems by harboring pests and diseases, interfering with harvest operations, and increasing cost of cleaning and drying the crop produce. For efficient and profitable crop production, appropriate weed management is essential.

 

Until the mid-19th century, labor-intensive and rather inefficient hand weeding was the only form of control. Later, mechanical measures for weed control were introduced. But only the discovery of selective herbicides in the 20th century eliminated the tedious and demanding task of non-chemical weed control in many countries. These products contributed to substantial increases in yield and consistency of crop production.

 

Chemical weed management must be achieved without causing damage to the crop. This is referred to as “selective” weed control. Selective herbicides have been derived from a wide range of different chemical classes with varying modes of action. In some cases, “safeners” (eg. Cloquintocet) have been developed. These protect a given crop from potential damage caused by a specific herbicide. Selective herbicides have allowed the intensification and spread of key crops such as corn, rice, soybeans and wheat.