A system (202) for applying an herbicide to an agricultural field includes a sensor (114) configured to measure total vegetation density in the agricultural field; and an applicator vehicle (102, 302) comprising a chassis (104), a liquid holding tank (110) carried by the chassis, and at least one nozzle (204) carried by the chassis and in fluid communication with the liquid holding tank. A controller (116) is configured to control an amount of flow of herbicide through the nozzle(s) (204) based on the total vegetation density measured by the sensor. A method of applying an herbicide to an agricultural field includes measuring a total vegetation density in the agricultural field and spraying a variable amount of an herbicide through at least one nozzle onto the agricultural field. The amount of herbicide is based on the measured total vegetation density, without regard to distinction between crop and weed.