Sustainable control of powdery and downy mildew diseases of grapevine and impacts of control on wine quality and vineyard health

Abstract

Evaluate milk, whey and other alternativefungicides for use in management of powdery and downy mildew. Investigation of effects of treatments on juice and wine, and on microflora and beneficial arthropods in the vineyard.

Summary

Grapegrowers and winemakers have sought improved management of powdery mildew and downy mildew, both of which cause production losses and can affect quality of grapes and wine. Another reason for this project, which looked at novel ways of controlling these two major fungal diseases, was the quest for new spray options to reduce reliance of commonly-used chemicals. Previous research at the University of Adelaide identified milk, whey and canola oil as having potential to control powdery mildew even in seasons of high disease pressure such as 2001-2002. A need was seen, however, to examine the efficacy of novel treatments in replicated field trials. Mildew infections on leaves and bunches grown in similar conditions but with different control treatments were measured at frequent intervals through the season. Finally bunches were collected and winemaking characteristics of importance like pH, titratable acidity and sugar were measured. The trials extended across different climatic conditions. Results were encouraging but variable. For instance, application of milk, whey and Ecocarb plus Synertrol Horti-Oil controlled powdery mildew to levels not significantly different from those provided by sulfur on Shiraz and Verdelho in South Australia and on Cabernet Sauvignon in NSW, although these products did not provide adequate control of powdery mildew on Pinot Noir in Tasmania. All products evaluated for prevention of downy mildew on inoculated vines reduced disease incidence and severity compared with untreated, inoculated controls. Ferrous formulations as well as tea-tree oil based products and Ecocarb plus Synertrol Horti-Oil performed as well as the standard copper fungicide treatment. No adverse influences on wine were found. The outcome for the industry is potential for use of novel products. This potential may be increased with experience and timed to suit canopy structure and level of infection as it was found effectiveness was generally greater when disease pressure was moderate to low and when thorough foliage coverage was possible. tensive soil sampling was undertaken in vineyards at Nuriootpa and McLaren Vale at different depths and at various distances from the trunks of Shiraz vines. Irrigation practices examined were conventional drip irrigation, partial rootzone drying (PRD), and use of normal water sources as well as reclaimed wastewater (i.e. treated domestic sewage). Particular interests were the distribution and health of roots and whether there was any greater susceptibility to soil-borne pathogens under strategic irrigation practices. Results of root distribution analyses confirmed that the majority of roots were located at 10 to 30 cm down the soil profile and that vines under standard drip had slightly greater root density compared to PRD but similar distribution. This distribution was not affected by use of reclaimed wastewater, however, and wastewater caused no significant change to microbial activity in the area of greatest root concentration. In addition, standard drip applications and PRD were found to have no detrimental effect on root health. Although it had been thought that the alternate wetting and drying of PRD might increase susceptibility to root infection by soil-borne fungi this did not appear to be the case. Important outcomes for the industry are knowing PRD appears to be sustainable and that reclaimed water can be viable for vineyard irrigation.