Pesticide Dose Adjustment in Vineyard Spraying and Potential for Dose Reduction

The adjustment of pesticide dose rates according to canopy size and leaf area density is not encouraged by current label formulations. However, experimental evidence shows that the application of a constant dose per unit ground area consistently results in average foliar deposits that are inversely proportional to the leaf area index (LAI) of the crop. Several methods for dose rate adjustment have been proposed, including the CH, LWA, TRV, and TAD models. The objective of this paper was to analyse the potential of the LWA (Leaf Wall Area) method for reducing deposit variability in espalier vineyards. A set of 42 deposition tests was analysed, performed during 1993 to 2005 using a uniform methodology for canopy and spray deposit assessment. Normalised deposits were calculated, assuming a constant dose either per unit ground area, and per unit LWA, respectively. The results showed that the LWA method has the potential of reducing deposit variability, compared to the fixed dose, conventional method (C.V. = 36% and 13%, respectively). Variations in canopy width and leaf area density scarcely affected mean deposits as long as the leaf layer index was LLI < 4. A decrease in mean deposits could be observed only for very thick and wide canopies with 4 < LLI < 6, which were otherwise not recommended, based on best agronomical practice.