Which effect has Herbicide Persistance in the Soil ?
Herbicides with long residual effect exert selection pressure on weed populations longer than herbicides that easily dissipate in soil. This is probably one of the reasons why weed populations resistant to a group of herbicides as new as the sulfonylureas have been found. If the herbicide is not very persistent, the seed bank in the soil may decrease the probability of proliferation of the resistant biotypes by keeping an elevated population of susceptible individuals that germinate and reproduce once the herbicide has lost its biological effect. Herbicides that are inactivated immediately in the soil are not necessarily free of resistance problems. For example, there are weeds resistant to paraquat; these resistant biotypes occurred often regular and continuous applications of paraquat, a condition which is equivalent to a high selection pressure.
