Sectioning remote imagery for characterization of Avena sterilis infestations. Part B: Efficiency and economics of control

Abstract

Avena sterilis weed pressure categories can be discriminated in wheat through remote images taken at late stages of wheat senescence. Site-specific image processing was achieved with SARI^®, an add-on software program for ENVI^® developed to implement precision agriculture. Using the SARI software and crop-weed competition and economic models, the precision yield losses for each micro-plot can be estimated and herbicide prescription maps obtained. Simulation studies on control indicators and herbicide use efficiency were undertaken using real-time ground data and remote images of two wheat plots infested with Avena sterilis at LaFloridaII and Navajas (Southern Spain). The simulation indicated that precision application of herbicides would produce higher overall herbicide savings (OHS) compared to broadcast applications but would vary depending on the level of weed infestation, the decision making criteria (DMC) of applying herbicide above a weed infestation level and the size of the spray grid considered. For example, for areas with low levels of infestation (around 15%), the OHS was 20, 44, 81 and 90% for a DMC of 0, 10, 20 and 30%, respectively. SARI^® also estimates the overall herbicide application efficiency (OHAE), a key agro-environmental index to estimate the efficiency of herbicide applications in weedy areas and the lack of herbicide applications in weed-free areas. Ideally, the OHAE is equal to 1 if weed control is complete and herbicide applications in weed-free areas are not necessary. The OHAE index is influenced by the size of the micro-plot and decision-making herbicide application criteria (DMC). The OHAE values increased as the size of the micro-plot decreased, regardless of the intensity of the weed infestation. For example, micro-plots of 20 × 6 m, 5 × 3 m and 1.2 × 1.5 m had OHAE values of 0.27, 0.57 and 0.76, for areas of low infestation, when averaged over the DMC. Generally, the OHAE values increased as the size of the micro-plot decreased regardless of the intensity of weed infestation. Based on actual weed abundance data, competition models and production costs, SARI^® estimated wheat yield losses and economic net return for each micro-plot and herbicide application strategy. In both locations, weed infestation varied spatially from virtually weed-free micro-plots to 15 and 24% winter wheat yield loss in Navajas and LaFloridaII, respectively. Preliminary calculations indicate that net returns were slightly higher for areas with site-specific adjusted-rate applications than for the overall standard label rate application strategy. Both of these strategies provided considerably higher net returns compared to non-treated areas.