Dosage of plant protection products adapted to leaf area index in viticulture

Abstract The efficacy of plant protection products depends on many factors. Among them, the dose of active ingredient, the size of deposits, the number of deposits and the dose per deposit on the leaf surface are very important elements for successful control of diseases. For crops, such as grapevine which develops a large canopy within a relative short period of time, the dosage is generally adapted to the growth stage of the vine or a unique dose is applied during the whole growing season. These can result in over- or under-dosage of plant protection products, with economic and environmental impacts, reduced efficacy or increased risk of resistance. The aim of the new dosing concept is to apply the amount of product necessary to control diseases and pests and avoid over- and under-dosing. Key elements of the leaf area index based dose model are knowledge of the leaf surface at the day of application, the application quality of the equipment and the dose–response curve of the applied product. Based on several field experiments and measurements on different grape varieties, a correlation between the effective leaf area, the shoot length and the vine row volume (VRV) was established and used as an indirect method to determine the leaf area index (LAI). Dose–response experiments for folpet and azoxystrobin against downy mildew allowed the amount of active ingredient per leaf area unit for good efficacy to be determined. The average LAI-dependent deposit capacities of different commercial sprayers were measured in farm experiments and a dosage table established to adapt the amount of active ingredient to the LAI. Applying the LAI-adapted dosage, no differences in efficacies could be obtained on season-long spraying programs with commonly used fungicides against downy and powdery mildews, compared to recommended dosages. The data demonstrate that independently of the growth stage of the vine, a more or less constant amount of active ingredient, obtained from the dose–response experiments, was deposited on the leaves using the LAI-adapted dosage, in contrast to the standard dosage.