No abstract

Grapevine leafroll disease (GLD) is caused by a complex of vector-borne virus species in the family Closteroviridae. GLD is present in all grape-growing regions of the world, primarily affecting wine grape varieties. The disease has emerged in the last two decades as one of the major factors affecting grape fruit quality, leading to research efforts aimed at reducing its economic impact. Most research has focused on the pathogens themselves, such as improved detection protocols, with limited work directed toward disease ecology and the development of management practices. Here we discuss the ecology and management of GLD, focusing primarily on Grapevine leafroll-associated virus 3, the most important virus species within the complex. We contextualize research done on this system within an ecological framework that forms the backbone of the discussion regarding current and potential GLD management strategies. To reach this goal, we introduce various aspects of GLD biology and ecology, followed by disease management case studies from four different countries and continents (South Africa, New Zealand, California-USA, and France). We review ongoing regional efforts that serve as models for improved strategies to control this economically important and worldwide disease, highlighting scientific gaps that must be filled for the development of knowledge-based sustainable GLD management practices.

Grapevine leafroll disease in New Zealand is predominantly caused by the ampelovirus GLRaV3 which is vectored between vines by up to three species of mealybugs (Pseudococcus spp) However global understanding of the transmission and spread of GLRaV3 remains limited and does not definitively show how to successfully manage the disease in New Zealand The disease is a manifestation of a complex relationship between the virus vine and vectors each component of which is interdependent on the other two The review suggests that a full understanding of the disease will require research and operational input from plant virologists entomologists vine physiologists pest controllers vineyard managers grapevine breeders/improvers and winemakers Such a wide range of expertise should ensure that the factors behind the spread of the disease over time (its epidemiology) are accurately determined and that effective management solutions are delivered over the course of decades

Grapevine leafroll-associated virus 3 (GLRaV-3) negatively alters grape yield and wine quality but adopting practical control actions could avert an epidemic. In 13 New Zealand commercial vineyards that were planted with one of five red berry cultivars (n = 29,943 vines), we assessed if roguing (removing) GLRaV-3-infected vines could reduce and maintain incidence at <1%. In 2009, baseline GLRaV-3 incidence ranged from 4 to 24%. Annually until 2015, we visually diagnosed and rogued vines with foliar symptoms of GLRaV-3, and monitored vine populations of the virus vector, the mealybug Pseudococcus calceolariae. In 2009, 2544 symptomatic vines (12%) were rogued but with incidence declining year-on-year, just 408 vines (1.4%) were rogued in 2015. Mapping virus spread annually showed within-row vines immediately either side of an infected vine ('first' vines) were most at risk of vector mediated transmission, but a temporal decline in these infections was observed. In 2010, 26% of 'first' vines had foliar symptoms, reducing to 6% by 2015. Overall, GLRaV-3 management outcomes were variable. In six vineyards, symptomatic vine incidence reduced to <1% within 3 years of roguing commencing. By contrast, roguing did not contain virus spread in another two vineyards, where cumulative vine losses of 37 and 46% to 2011 and 2013, respectively, was deemed economically unsustainable by the owners who removed all remaining vines. In the remaining five vineyards, annual incidence was consistently ˃1%. In demonstrating the importance of low vector pressure to successful virus control, we emphasise the need to adopt a multi-tactic response targeting virus and vector populations annually.

The ratio of catch in traps in the corner and centre of a 16-trap array at different spacings offers a rapid preliminary assessment method for determining the potential for mass trapping. Additional knowledge of vital rates and dispersal is needed for predicting population suppression. Our approach should have value in mass trapping development. © 2014 Society of Chemical Industry.