Spatial variation in response to 'reduced input' spray programs for powdery mildew and botrytis identified through whole-of-block experimentation

Background and Aims: Previous work has highlighted the utility of the whole-of-block approach to viticultural experimentation. Here, we use this approach as a means of evaluating alternative spray programs for managing two economically important grapevine diseases at commercial scale.

Methods and Results: Two experiments were conducted in vineyards in the Coal River and Rokeby districts of Tasmania. The first, carried out in a 4.5 ha vineyard planted to Vitis vinifera L. cv. Pinot Noir, sought to evaluate fungicide programs for control of powdery mildew (Erysiphe necator), in particular with a view to reducing the amount of sulphur applied in organic production systems. The second sought to evaluate the benefit (if any) of changing the time of fungicide application from flowering to pre-bunch closure for the control of botrytis bunch rot (Botrytis cinerea) in a 2.4 ha Chardonnay vineyard. In both cases, treatments were applied to a whole-of-block experimental design using commercial spray equipment. Disease severity and the response to the various spray treatments, was spatially variable and related to topographic variation. Botrytis severity was also related to vine vigour. The powdery mildew results supported the retention of sulphur in organic spray programs, while Switch® (Syngenta Group, Basel, Switzerland) applied at pre-bunch closure in the botrytis experiment reduced disease severity relative to the application at flowering. Spatial variation in the response to the latter treatment, when examined four times pre-harvest, suggested that secondary spread may not have been an important mechanism for increasing disease severity over time.

Conclusions: Consistent with the other work described in this series of papers, we conclude that the whole-of-block experimental approach offers both researchers and vineyard managers a means of acquiring more useful information than would be obtained from a conventional plot-based approach.

Significance of the Study: This study highlights the value of collecting spatially distributed data as a means of better understanding the incidence, spread, progression and control of fungal grapevine diseases. As such, it provides a new application for this experimental approach, which enables spatial variability to be used as an experimental tool.