Assessment of nozzle control strategies in weed spot spraying to reduce herbicide use and avoid under- or over-application

Abstract

Spot spraying is a method that can meet the objectives of reduced herbicide by maintaining a high level of weed control efficiency without lowering crop yield and harvest quality. Individual nozzle control systems show great potential for herbicide reduction. Nevertheless, this method of application also entails the risk of under-application on weed surfaces because of the lack of spray overlap and irregular dosing. Thus, nozzle control strategies need to be refined and assessed, regarding herbicide reduction and the ability to apply the prescribed dose on the target surfaces. Six control strategies were considered by activating complementary adjacent nozzles or increasing the flowrate of specific nozzles. Theoretical analyses and simulations were carried out to compare these strategies using three indicators. Considering a simplified description of the weed spatial distribution, a herbicide reduction indicator was expressed analytically for each strategy as a function of the weed coverage rate and patch width. For each strategy, numerical simulations were also carried out to compute under- and over-application indicators considering six weed coverage rates, eight patch widths and six different spray patterns. Graphs and charts were developed to provide convenient tools to help select the best technical approach for reducing chemical applied whilst keeping the prescribed dose on targets. In particular, a good compromise could consist of setting the weed detection width (associated with each nozzle) at twice the nozzle spacing and using triangular spray patterns combined with double spray overlaps. • Six nozzle control strategies are compared for herbicide spot spraying. • Herbicide reduction is modelled analytically by weed patch and spraying features. • Herbicide misapplications are assessed using numerical simulations. • Setting the detection width at twice the nozzle spacing is a good compromise. • Triangular spray patterns combined with double overlaps are preferred.