**1. Introduction**

Weed control defined as any method trying to stop weeds, especially noxious or injurious weeds from competing with desired plants. The evolution of weed control began many years ago when humans felt that it was necessary to remove and dispose of weeds in order to reduce their competition with the planted crops and thereby increase the yield qualitatively and quantitatively. Weed control involves processes where weed infestations are reduced, but not necessarily eliminated. In weed control, the degrees of control can be described by the state of weed reduction ranging from poor to excellent. The degrees of control depending on the types of weeds involved and the effectiveness of the control method adopted. It should be noted that in weed control, the weeds are generally not completely killed, however, their growth is somewhat contained while the crop continues a normal yield. Weed control is aimed at only reducing the weeds present by employing some form of

control measures. On the contrary, weed management is a systematic approach where the whole land use planning is carried out in advance to minimize the very invasion of weeds in aggressive forms and give crop plants a strong competitive advantage over the weeds. Weed control methods can be grouped into the culture, physical, biological and chemical [1]. Human efforts of controlling weeds began with the use of cultural practices such as tillage, planting, crop rotation, fertilizer application, irrigation, etc., that are adapted to create favorable conditions for the crop. If properly used, the practices can help in suppressing weeds. On the other hand, culture methods alone, cannot control weeds; it can only help to reduce the weed population. Culture methods therefore, can be effectively used in combination with other methods. Every method of weed control has its own advantages and disadvantages. No single method is successful under all weed situations. Most often, a combination of these methods gives effective and economic control than a single method. These methods of controlling weeds were later developed in the form of mechanical weed control such as hand pulling, hand hoeing, and planting in rows to facilitate machinery use, but again these methods did not attain the desired benefits [2].

Later, a new mechanism of weed control was developed through the use of chemical inputs. Chemical weed control began on a small scale. Since the 19th century, a combination of salt and ash powder was used to control weed plants which grow on either side of the railway. The use of synthetic herbicides, however, begun in the 1940s with the development of some organic herbicides, specifically the 2,4-D. This herbicide is considered as a growth regulator used in high doses to control broadleaf weeds [3]. Then, chemical weed control was widely used as a form of weed control and achieved a dominant role in the crop management, more efficient, economical and low costs as compared to other methods and contributed strongly to the increase in the agricultural yields and reduce losses due to weeds [4, 5]. As a result of using chemical weed control, the traditional method of weed control such as cultivation and hand weeding has been greatly been decreased [6]. A new method to control weeds was created by producing different types of synthetic herbicides according to the mode of action of these compounds against weed plants. By 1990s, the number of compounds that have been used in herbicides in many different formulas reached to more than 180 compounds [7]. According to a report of [8], the total value of the global's agrochemical market was between 31 and 35 billion US\$ and of the products, herbicides accounted for 48% followed by fungicides at 22%. Nowadays, chemical weed control becomes as an integral part of the complex world of technical inputs required for modern agricultural production and have been accepted as a standard tool of the trade by farmers throughout the world despite the negative effects of synthetic herbicides on the ecosystem [1].
