Effect of organic, biodynamic and conventional vineyard management inputs on grapevine growth and susceptibility to powdery mildew and Botrytis bunch rot

Abstract

Interest and uptake of organic agriculture (including biodynamics) has continued to increase with 37.5 million ha of agricultural land dedicated to these systems worldwide (IFOAM, 2014). Whilst the use of organic inputs and systems in vineyards is becoming increasingly better researched and reported, little reliable research exists for the same in biodynamic viticulture; especially in regard to disease control. It is claimed that using biodynamic inputs can control powdery mildew and Botrytis bunch rot, two of the more economically important diseases in Australian viticulture. This study investigates the efficacy of these inputs, compared with those used in organic and conventional approaches. To this end three trials were established in 2010 in South Australia; two pot trials at the University of Adelaide Waite Campus, Urrbrae, Australia and the third in a commercial Cabernet Sauvignon vineyard in the McLaren Vale wine region, Australia. At the Waite trial site six treatments (2 organic, 2 biodynamic, 3 conventional and 1 control) were applied to a split plot design. Each treatment was replicated in three blocks, on three vines per treatment, to newly propagated cultivars of Chardonnay and Shiraz vines (Vitis vinifera L.). The same cultivars and a similar split plot design were used in a growth room trial in the winter of 2012. Four treatments of recommended herbal extract ‘teas’ from the biodynamic literature (Yarrow, Nettle, Equisetum and a combination of all three) and two controls (water and synthetic chemicals) replicated four times, were applied. In McLaren Vale an established trial site was utilised. Four treatments (organic, biodynamic, high input conventional and low input conventional) were applied to 20 year old Cabernet Sauvignon vines in a randomised split plot design replicated in four blocks. To assess the effect of compost, each management treatment was also separated to include both a plus and minus compost treatment. Non-destructive assessment of powdery mildew severity was evaluated over three seasons at the Waite trial and Botrytis severity data via detached bunch assay were collected in the final season. Additionally selected growth data were also recorded; including nutritional status at flowering, harvest and mean bunch and berry weights, cane length and pruning weights to measure the effect on growth. Similar sets of data were recorded in the McLaren Vale site. Severity of powdery mildew and Botrytis bunch rot data only were collected from the growth room trial. In the wet and humid conditions of 2010-11, disease severity was high, in both field trials, across most treatments and the results were largely inconclusive. From the remaining two seasons in the field trials, the effects of the inputs on disease severity followed a consistent pattern in most situations. In the potted trial, plant extracts exhibited effective early season control of powdery mildew and reduced severity of Botrytis. In the McLaren Vale site, powdery mildew was found in only one of three years and the study of Botrytis was inconclusive. In both field trials, plant growth parameters suggested that conventionally grown vines were generally larger and more productive than those grown organically or biodynamically. The growth room trial suggested an acceptable level of powdery mildew control in response to a combined plant extract application when compared with conventional inputs. Encouraging results from this trial would suggest benefits in the use of some BD extracts, but further field testing will be required. This study is the first study to compare biodynamic disease control inputs with the well-established conventional and increasingly accepted organic options. As some sections of the Australian Winegrape industry seek alternative disease control inputs, the biodynamic preparations examined here may be a viable option to augment established practices.