Wild blueberry yields are highly dependent on agrochemicals for adequate weed control. The excessive use of agrochemicals with uniform application in significant bare spots and plant areas has resulted in increased cost of production. A cost-effective automated prototype variable rate (VR) sprayer was developed for spot-application (SA) of agrochemicals in a specific section of the sprayer boom where the weeds have been detected. The weed patches were mapped with an RTK-GPS receiver in test tracks before and after kaolin (colored dye additive) application in the spray liquid to evaluate the performance accuracy of the VR sprayer. The application rate was set up at 187.0 L/ha. The selected buffer (before and after) was 25.4 cm and average ground speed was 6 km/hr. These maps showed that chemical was sprayed on all targets (weed patches) precisely in selected tracks in both fields. The water spray was replicated three times with both SA and uniform application (UA) in selected tracks of a wild blueberry field to evaluate the repeatability of the sprayer and to quantify the chemical saving with SA. Results showed SA rates ranged from 45.5 to 53.0 L/ha (SE = 3.20) in track 1 and from 26.5 to 29.4 L/ha (SE = 0.88) in track 2. The UA rate varied from 160.70 to 161.70 L/ha (SE ranged from 0.16 to 0.37) in both tracks. The reason of variation in SA rates might be some weeds were damaged due to repeated passes of vehicle in the tracks and ultrasonics could not detect the shorter (damaged) weeds.

The chemical saved with SA was 69.22% with 22.67% weed cover and 82.50% with 18.13% weed cover in track 1 and in track 2, respectively. Based on these results, the VR sprayer could be used for in-season SA of agrochemicals in wild blueberry cropping systems to significantly reduce the amount of agrochemical usage and also reduce environmental pollution.