Development of prototype automated variable rate sprayer for real-time spot-application of agrochemicals in wild blueberry fields

An automated prototype variable rate (VR) sprayer was developed for control of 8 individual nozzles on a 6.1 m sprayer boom for in-season, site-specific application of agrochemicals on weeds. The sprayer boom was divided into 8 sections and mounted behind an all-terrain vehicle (ATV) at 76.2 cm above the ground. The variable-rate control system consisted of 8 ultrasonic sensors (one per spray section) mounted on a separate boom in front of the ATV, DICKEY-john Land Manager II controller and flow valve, solenoid valves and an 8-channel variable rate controller interfaced to a Pocket PC (PPC) using wireless Bluetooth® radio with Windows Mobile® compatible software. This type of VR sprayer does not use prescription maps, but relies on sensors to provide real-time weed detection information which is used to dispense correct agrochemical rates for the weeds. The sprayer can be used for in-season, spot application (SA) of agrochemicals by activating specific boom sections where the weeds have been detected.Two wild blueberry fields have been selected in central Nova Scotia to evaluate the accuracy of the VR sprayer. Water sensitive papers (targets) were stapled to weeds randomly selected in two tracks of each field. The papers were orientated parallel to the ground. The percent area coverage (PAC) of the sprayed targets with both SA and uniform application was calculated by an imaging system. Non significance of the t-test for uniform versus SA targets PAC indicated that there was no significant bias in the SA and that the SA was accurate. The PAC with both applications ranged from 10.01% to 81.22% and from 5.39% to 72.67% in field 1 and field 2, respectively. Weed heights at selected points were measured and related with percent area coverage to examine the sprayer performance for spray application. Linear regression analysis showed that weed heights were significantly correlated (R2 ranged from 0.60 to 0.75) with percent area coverage of the targets in selected fields with both applications. It is proposed that herbicide should be applied at early stage of weed growth (weed height ranged from 35 cm to 55 cm and plant height ranged from 12 cm to 30 cm) for appropriate application with these specific VR sprayer arrangements. Based on these results, the VR sprayer was efficient and accurate enough for spot-application of agrochemicals usage in wild blueberry fields.

Research highlights
► VR sprayer is efficient and accurate enough for spot-application of herbicides.
► Control system of VR sprayer proved efficient at an actual lag time of 0.05 s.
► Automatic compensation for changing ground speed – no need to manually readjust sensors.
► Adjustable front and back buffers for precise overlapping of applications on targets.