Spray retention variaility by barley

The effectiveness of a phytosanitary treatment depends on the amount of product actually retained by the plant leaves relative to the volume per hectare applied. Parameters affecting spray retention include application variables such as nozzle type, operating pressure and formulation, and target properties such as species and growth stage. These variables condition more specific parameters such as the number of droplet impacts by unit area of leaf, the droplet size and velocity distributions at impact, droplet physicochemical properties (dynamic surface tension and viscosity) for the application variables and leaf wettability and plant architecture for the target. During a uniform treatment of the crop, each plant receives various droplet distributions that behave differently during impact depending on its architecture. In consequence, this contributes to increase the varying retentions observed between plants in field trials, leading in practice to apply an amount of product always greater than required to provide the level of crop protection needed for insuring high yields. The aim of this paper is to observe the retention variability that can occur during a treatment depending on the equipment, tank mix formulation and crop properties. The spray retention variability was assessed for three tank mix formulations: tap water, tap water with break thru, and tap water with Li700. For each formulation ten sprays were realized on five barley plants at the two leaves growth stage (BBCH stage 12) grown indoor in controlled conditions and ten sprays realized on individual barley plants at the same growth stage. The amount of spray actually retained by barley plants was assessed by dosing a fluorescent tracer added to the mixtures. Barley plants were placed linearly below the center of a moving nozzle at the speed of 2m/s using a pressure of 2 bars. The last step was measuring leaf area for each spray and calculating the amount of sprays retained by barley plants to determine the variability of spray retention.