Farmers and agriculturalists often note that the use of the same herbicide for several seasons becomes inactive against the targeted weed species and soon it is judged that this herbicide has become ineffective. The real reason behind this is increasing the growth and reproduction of weed species that can survive which is technically known as (Weed Resistance).

 The phenomenon of weed resistance to herbicides is the most important problem facing weed chemical control which is considered as the ability of a certain genotype belonging to one of the weed species to survive, while the other genotypes of the same weed species are affected.

The weed resistance does not mean the poor performance of the used herbicide as much the difference in the genetic diversity, which allows some of the genotypes to survive and produce new generations while the other genotypes are killed. These resistant genotypes often survive even if the herbicide is used in a higher dose than the recommended dose.

On the other hand, herbicides are different in terms of the controlling mechanism to weed, so the weed resistant species can be resistant to other herbicides which used the same controlling mechanism.

Currently, there are more than 249 weed species that are resistant to herbicides over the world which are distributed in 47 countries according to the latest reports. These numbers increase annually with the development of new resistance.

Strategies of reducing the development of weed resistance to herbicides include several things which are:

1- Applying the principle of Integrated Weed Management

IWM is known as the technic of using more than one method to reduce weed competition using alternative methods to act with or without herbicides such as planting varieties that are characterized by their high competitive to weed or crop rotation.

-2  &l