Volume 3, Issue 9 (October 2006)
Impact of Adjuvants on Droplet Spreading and Droplet Deposit Area After Spray Application
The effects of adjuvants on spreading of small droplets after spray application and of larger drops with volumes in the microliter range was studied. The characterization of spreading as affected by adjuvants is done often with lab tests on artificial surfaces. In these tests much larger drops in the microliter range are used and plant factors such as the presence of hairs or crystalline waxes and spray related factors such as rapid evaporation, a different drop size magnitude, a drop size distribution in reality, and effects of adjuvants on drop size are not considered. For a set of test compounds from different chemical classes we evaluated stepwise the approximation to real systems with plant surfaces representing the major surface features. With larger drops of 10 and 20 μl we obtained a surprisingly good correlation of spreading on Parafilm® M and the mature leaves of Chlorophytum, tomato, rape, and corn. With good wetters better spreading was observed on leaves than on Parafilm M. The correlation of spread diameters with real spray (flat fan nozzle, 300 l/ha) on an easily wettable plant and drops on Parafilm M was very good as well though with the best spreaders the gravimetric momentum on spreading and longer times for evaporation overestimated spreading of the larger droplets on Parafilm M. If the mean spread diameters of real spray was plotted vs. the logtransformed spread diameter on Parafilm M a linear correlation was obtained (r2=0.92).