Selective applications of weed control chemicals

In a chemical dispensing apparatus for applying herbicide to weeds through a spray nozzle, weed identification means for determining the probable presence of weeds within a field-of-view of an optical sensor carried by said apparatus wherein the determination of the probable presence of weeds is effected by said weed identification means based on reflectance values of the field-of-view taken from a plurality of bands within the electromagnetic spectrum, as sensed by the optical sensor, and wherein the reflectance values so obtained are used by the weed identification means to generate an extended chromatic vector that characterizes the chromatic content of the field-of-view, and includes an uncoupled, orthogonal infra-red value which vector is then compared by the weed identification means to established chromatic vector values provided therein that characterize the probable presence of weeds within the field-of-view and thereby provide an indication as to whether a weed is probably present within the field-of-view.