Assessing the foliar deposition on greenhouse tomato plants

The paper reports the results of some trials aimed at measuring, under field conditions, the foliar deposition on full developed tomato plants when using a spray lance in ordinary working conditions: pressure of 20 bar, volume rate of about 1000 L/ha, forward operator movement. Experimental tests were carried out spraying a water solution with 2% of food dye Poinceau Red E124 as a tracer and 0.05% of a surfactant. Foliar deposition was assessed by measuring, via a spectrophotometric technique, the amount of tracer collected by a number of leaves (48 per replicate) representative of the whole canopy. Moreover, to assess the deposition on both leaf surfaces, some artificial targets (48 per replicate) were fixed to upper and underside of 24 leaves. After mixture application, the artificial targets were analysed by means of an image analysis system to measure the surface covered by spots. The results showed a mean foliar deposit value of 1.253 μL/cm2 and coefficients of variation ranging from 49% up to 87%. The lowest deposit was observed on the high–internal layer of the canopy (0.680 μL/cm2, only the 54% of the mean value), where the plants had the highest values of Leaf Area Index and Number of Foliar Layers. The artificial target analysis showed a better coverage of the upper side foliar surface in each sampling location, ranging from 1.1 to 4.8 that of the under side.