Vineyard-wide control of grapevine leafroll-associated virus 3 requires an integrated response

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.