Grapevine scale has been increasingly problematic in vineyards of southernt Australia over the past few seasons. Scale are soft-bodied insects that feed on plant sap; high numbers in a vineyard can significantly reduce vine health and grape yield.
Sooty mould on Chardonnay grapes
As scale insects feed, they excrete a sticky substance derived from the sap of the vines called ‘honeydew’. Honeydew in turn attracts ants and provides a substrate for sooty mould, which is a fungal infection caused by several fungal species where all parts of the vine, including the grapes, can become blackened (as if covered in a fine layer of soot). Presence of sooty mould on grapes above a threshold level (commonly 3 per cent) can result in grapes being downgraded or rejected by wine producers, potentially causing significant economic loss for grapegrowers.
The current control method used by many growers is an oil spray during vine dormancy, but this has limited efficacy due to the high numbers of scale that over-winter under the bark of vines. In addition, insecticide application can be detrimental to overall control because of its impact on beneficial insect populations.
Understanding scale and sooty mould
Scale insect cluster in spring
Grapevine scale and associated sooty mould
Recent studies on scale and sooty mould, funded by Wine Australia, have attempted to unravel the cause of increased incidence of scale and sooty mould. Reports from these projects can be found on the right-hand side of this page.
A three-year project carried out by the SA Central Regional Program, funded by Wine Australia, aimed to survey the impact of scale on vine vigour and fruit quality and to provide control options for grapevine scale. The final report for this work, carried out by Jenny Venus, can also be found on the right-hand side of this page.