ABSTRACT
The biological and environmental effects of herbicides and agronomic techniques are strictly interdependent. The former is primarily human mediated and biologicalally and agronomically more dangerous because it involves species that are less well known in the invaded site. The most important cropping practices that determine the environmental impact and agronomic performances of herbicides are tillage system, crop rotation, and fertilization. Agronomic practices that reduce erosion are therefore effective in reducing herbicide losses only for molecules with a high organic carbon and water. Knowledge of the cost of weeds is therefore a fundamental step towards assessing the efficiency of current control methods and provides a rationale for allocation of resources for research and development of new herbicides and technologies. Water, light, and mineral nutrients are the major resources for which weeds and crops compete, and their availability strongly influences the competitive ability of plants and consequently weed flora composition.
