Comparison of spray deposits and efficacy against powdery mildew of aerial and ground-based spraying equipment in viticulture

Poor control of fungal diseases can be related with the application of fungicide which is difficult in steep vineyards . Spray distribution using a tracer obtained with a standard axial fan sprayer was compared to that of a large volume air blast sprayer, a helicopter, an over-row sprayer, a tunnel sprayer (recycling, not air assisted) and a motorized knapsack mistblower. Field experiments were conducted over two years in a flat area as well as in a steep vineyard on large experimental plots. A whole season spraying program with each equipment was applied on separated plots with powdery mildew assessed regularly and compared to unsprayed controls in order to correlate leaf deposits with the biological efficacy. The highest deposits on leaves were obtained using the tunnel sprayer, the knapsack mistblower, the axial fan sprayer and the over-row sprayer. The lowest losses to the ground and airborne drift were with the recycling sprayer and knapsack mistblower, in contrast to the helicopter and the large volume air blast sprayer. With all tested sprayers, except for the helicopter, losses to the ground were lower under a fully developed canopy than at the four-leaf stage. The tunnel sprayer gave the best prevention of drift and the best deposit on the upper leaf surface . Control of powdery mildew with fungicides applied at the same spray intervals was good with all sprayers, except for the helicopter and the large volume air blast sprayer. Powdery mildew control was better when the deposit was more even on both leaf sides. Economical losses can occur when inadequate spraying equipment is used and there is high disease pressure.