ABSTRACT
Farmers have increased post-emergent herbicide use since the 1960s, thereby replacing mechanical weeding methods and prophylactic practices according to the principles of integrated pest management. The use of herbicides, however, has not eliminated weed problems in agriculture (Haas and Streibig, 1982; Firbank and Watkinson, 1986) but has changed the weed composition and reduced the total population density (Chancellor, 1977). The frequency of herbicide-resistant or tolerant biotypes of weeds and the demands for lower herbicide residues in food, water, and soil have all increased since the 1970s, further reinforcing the need to develop weed management systems that minimize the use of herbicides. These concerns have given impetus in Europe to research and development into weed control measures that can reduce pesticide use. Site-specific weed management is an option with positive effects on the environment and economy. With a large within-field variation in weed occurrence, patch spraying based on the need for weed control may reduce treatment cost as well as herbicidal loading to the environment.
