Spray retention; Leaf orientation; Drop impact; Blackgrass; High-speed imaging
Abstract :
[en] Spray application efficiency depends on the pesticide application method as well as target properties. A wide range of drop impact angles exists during the spray application process because of drop trajectory and the variability of the leaf orientation. As the effect of impact angle on retention is still poorly documented, laboratory studies were conducted to highlight the effect of leaf orientation on drop impact outcomes. Measurements were performed with a high-speed camera coupled with a retro-LED lighting. Size and velocity of the drop were extracted by image analysis. Drop impact types were determined by the operator. Drops were produced with a flat-fan nozzle mounted on a movable ramp. Excised blackgrass [Alopecurus myosuroides HUDS. (ALOMY)] leaves were stretched between two parts of a U-shaped support. A surfactant (Break-Thru® S240) was sprayed to highlight the effect of mixture surface tension. The whole device was tilted from 0 to 90°. Relative volume proportions were computed within of an energy scale divided into 11 classes. These proportions have been weighted by an average volume distribution and the results were summed for all energy classes to obtain the total volume proportions for each impact outcomes and for all leaf angles. For distilled water (high surface tension) the increase of rebound proportion with the increase of drop impact angle is highlighted. For surfactant (lower surface tension), it results in an increase of drop fragmentation in Cassie-Baxter wetting regime. To be statistically representative, bigger drop samples should be used.
