FACTORS AFFECTING THE OPERATION OF THE WEED-SENSING DETECTSPRAY SYSTEM

Field experiments were conducted for 3 yr to determine the effect of v arious biological and physical factors on the operation of the weed-se nsing Detectspray system. Plant detection is achieved by sensors measu ring differential reflectance of red and near-infrared wavelengths of light from green plants, crop residues, and soil. Weed detection was g reatly reduced 70 to 80 min after sunrise and before sunset when opera ted at lat 50 degrees N because of reduced solar irradiance. Tall, den se-standing crop stubble limited detection of small weeds at the soil surface. Weed detection varied with plant species. Canola with three t o four leaves consistently was detected, but wheat or green foxtail us ually required five to six leaves to be detected. Small weeds were det ected if present at densities greater than 70 plants m(-2). Growers an d commercial applicators need to be aware of the limitations of the De tectspray system to use it effectively to control weeds with concurren t reductions in herbicide use.