Target detection as a tool of selective spray application on trees and weeds in orchards

A spectral detection system discriminating the targets from the non target area was tested during spray applications in apple and pear orchards. The objective of the test was to evaluate the accuracy of the system working at different application parameters and to estimate the rate of possible spray savings obtained during applications on the trees of different size and weeds of different density. The system consisted of the spray units equipped with optic sensors and a control unit which could operate up to 16 spray units. Each spray unit had an optic detector and two light sources emitting two beams of light at the wavelengths 670 and 750. The ratio between emitted and reflected light for each wavelength was the basis for discriminating between the presence or the absence of chlorophyll. The information was processed and used to control the electric solenoid valves opening or shutting off the nozzles. The target detection system worked technically properly. It enabled the selective spray application with spray savings adequate to the tree row profile. In intensive apple and pear orchards 16-25% reduction of spray volume was obtained. For herbicide applications the detection system discriminated weeds from the bare ground. Both sensitivity of the sensors and weed density had a significant influence on the spray savings. At medium sensitivity a considerable spray saving amounting 23% was obtained only on the plots with very low weed coverage (6%).