Target precision and biological efficacy of two nozzles used for precision weed control

Site-specific weed control at a high resolution level imposes high demands on the application technology in order to obtain a precise application and control of weeds in areas where threshold values are exceeded and to limit waste of herbicide in areas outside the intended sprayed area. The approach reported in this paper was to divide the field into small cells with a width of 250 mm. The other dimension in the longitudinal direction could be varied. The aim of the part of the study described in this paper was to test the precision of commercially available spray application techniques for the purpose of applying herbicides to decimetre-size cells. Two narrow angled nozzles, a TeeJet 4002 and a TeeJet 6502 were used in combination with the WeedSeeker valve. Two types of tests were performed, biological efficacy tests and droplet distribution tests. In the biological efficacy tests, efficacy of cell application at various places inside and at the border zone of the intended sprayed cell was compared with efficacy of a continuous application. The results of applications at 1 and 2 m/s showed that biological efficacy at positions in the central part of 160 mm long cells were comparable to efficacy obtained at the same positions using continuous application. In the spray distribution test, number and area of droplets in 10 × 10 mm cells were measured at different application speeds. From the distribution test, the displacement of the spray swath at increasing application speed could be described. Both efficacy and distribution tests showed a high precision targeting decimetre-size cells with the tested nozzle/valve combination at a low application speed. Increasing the speed above 2 m/s, increased variability of the application.