Abstract
Herbicide deposition rate can be affected by the leaf surface features of weeds and have a significant impact on the overall efficacy. In this paper, an orthogonal experiment was conducted to investigate the differences of droplet evaporation and spreading characteristics corresponding to weed leaf surface with hairy, waxy and rough (ridged) structures. Three weed species—Descurainia sophia, Lepidium lotifolium, and Lolium temulentum—were included in the study, representing these three leaf structures respectively. Glyphosate sprays with organic silicone surfactant in different concentrations were composed for the test. Single droplets with two diameters of 0.05 μL and 0.1 μL were deposited on the leaves to evaluate the evaporation and spreading characteristics. A digital camera was used and the evaporation duration and the maximum droplet coverage images could be captured and extracted from the recorded videos. The Image Processing Toolbox in Matlab was applied to segment the images for droplet and leaf background and the binary images’ pixel numbers were counted for coverage area calculation. The results revealed that the evaporation duration was reduced with the increase of the organic silicone concentration, while the spread area was expanded. The droplet spread more widely and evaporated faster on D. sophia leaves than on the leaves with L. lotifolium and L. temulentum surfaces. The spreading area and evaporation duration varied much faster on L. lotifolium leaves than on the leaves of other weed species. The droplet sizes affected spreading more significantly on L. temulentum leaf surface, as the spreading procedure of small size droplets was restrained by the groove structure. The results of this study would benefit the consideration of the farmers when selecting the proper nozzle code and the determining of the surfactant mixture in order to optimize the use of herbicides like glyphosate.
Highlights
IntroductionThere are variable control results of foliar applied herbicides in the field practice
The use of herbicides is important in preventing weed infestation [1]
We can conclude that the addition of surfactant could enhance the droplet coverage on weed leaves, which would enable the weed to absorb more active ingredient
Summary
There are variable control results of foliar applied herbicides in the field practice. Apart from some biotic factors like active ingredient and herbicide resistance, abiotic factors including temperature, rainfall, and deposition rate affect the efficacy of the foliar applied herbicides [2]. Agronomy 2019, 9, 547 amount of herbicide sprayed, and higher deposition rates benefit efficiency, since they allow a greater amount of herbicide available to be absorbed [3]. The absorption process is affected by various factors besides the deposition rate. These include environmental parameters (e.g., temperature, humidity), plant features (e.g., leaf structures, waxy layers), and spray liquid characteristics (e.g., surface tension, viscosity, chemical characteristics) [6,7,8]
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