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.     

Viticultural experimentation using whole blocks: evaluation of three floor management options

Background and Aims: Vineyard floor cover crops can affect vine vigour because of their requirement for soil, water and nutrients, as well as their interactions with pests and diseases. An on‐farm trial was established to identify the best floor cover management for an organically certified vineyard in the Clare Valley, South Australia, which was characterised by low vine vigour and yield. In establishing this trial, we also sought to evaluate a new approach to field experimentation in which the entire management unit is used for the experiment rather than small plots. Methods and Results: Three different floor covers were compared: the existing ryegrass cover crop with compost under the vine (control), ryegrass with mulch under the vine, and a replacement of the ryegrass with alternating mid‐rows planted to either cereal (Triticum triticosecale) or legume (Vicia faba), in both cases reverting to bare soil during summer. Spatially variable treatment differences were evident in the second and third year of the trial. The greatest benefits, in terms of enhanced yield and vine vigour, were induced by the cereal/legume treatment, although it was shown that only about half of the experimental area (i.e. only half of the entire vineyard) would have increased yields with the adoption of such a floor management strategy. Conclusions: The whole‐of‐block approach offers both researchers and vineyard managers a means of acquiring considerably more useful information than would be obtained from a conventional plot‐based experiment. In this particular vineyard, differential management with ryegrass retained in the southern part, but with the cereal/legume cover crop used in the northern part, is the ideal management practice. Significance of the Study: This study provides a novel demonstration of an approach that makes use of spatial variability as an experimental tool, and which enables experimental results to be acted upon in a way that recognises and exploits the underlying spatial variability of the vineyard.     

Spatio‐temporal dynamics of grape anthocyanin accumulation in a Tempranillo vineyard monitored by proximal sensing

Background and Aims: The spatio‐temporal variability of phenol grape composition in a vineyard can be characterised by using precision viticulture tools. Characterising anthocyanin variation in grapes requires a large number of observations, which can be done by using proximal sensors in the field. This study characterises the dynamics of spatial‐temporal variability in fruit anthocyanin content at different stages from veraison to harvest using a newly available non‐destructive fluorescence method. Methods and Results: The study was conducted in a Tempranillo (Vitis vinifera L.) vineyard (Navarra, Spain) during the 2010 season. A handheld, non‐destructive fluorescence‐based proximal sensor was used to monitor the anthocyanins of the berries at six different times between veraison and harvest. The fluorescence‐based anthocyanin indices were significantly correlated with the anthocyanin contents in berries (R² ranged from 0.74 to 0.78). The variability of the anthocyanin content decreased during the ripening period, reaching a minimum at harvest. Although the mean anthocyanin content of fruit increased from veraison until mid‐September, when a fairly stable value was reached that remained constant until harvest, spatial patterns within the vineyard changed over the whole ripening period. The spatial correlations between the anthocyanin content at each monitoring date and harvest time revealed that larger similarities in the spatial distribution of anthocyanins occurred at veraison and 10 days before harvest. Conclusions: Grape anthocyanins accumulated from veraison until around 1 month before harvest, whereas their spatial pattern within the vineyard changed throughout the whole ripening period. Significance of the Study: Knowledge of the spatial‐temporal variation of the anthocyanin content within a vineyard may assist decision making regarding sampling and vineyard management, especially if vineyard segmentation is employed.