Simulation-aided study of herbicide patch spraying: Influence of spraying features and weed spatial distributions

Abstract : Patch spraying is a technological way to reduce herbicide amounts required to control weeds by triggering spraying only where weeds lie. Nevertheless, the adoption rate of this technology by farmers is still low and there is a lack of efficient tools to assess patch herbicide applications depending on spraying features and weed spatial distributions. To avoid unrealistic in-field experiments, a virtual patch sprayer is designed and computer simulations are carried out to quantify herbicide reduction possibilities and assess the ability to apply the right rate on weed patches to ensure herbicide efficiency. The spray application simulator combines the theoretical description of the sprayer using various boom section widths (from 0.5 to 24 m) with experimental data describing various nozzle spray patterns obtained from three commercial nozzles. Virtual weed infestation maps are designed using random locations of weed patches with various spatial aggregation degrees modelled by different weed coverage rates and elliptical patch sizes. Simulation results are analysed through two performance indicators: i) the herbicide reduction ratio obtained with patch spraying compared to a uniform broadcast application (on the entire field area), ii) the proportion of weed patch area on which the application rate is higher than 85% of the prescribed application rate. Computer simulations enable to estimate a simplified relationship to quantify the reduction of herbicide use as a function of the weed coverage rate, the size of weed patches and the boom section width. This demonstrates that computer simulations provide practical tools to estimate the sprayer spatial resolution required to reach a given herbicide reduction target according to the weed spatial distribution. Simulations also demonstrate that the use of narrow section widths equipped with traditional nozzles leads to a significant proportion of weed areas exposed to herbicide under-application in the case of small patches.