The management and financial implications of variable responses to grapevine leafroll disease

© 2021, Società Italiana di Patologia Vegetale (S.I.Pa.V.). Grapevine leafroll-associated virus 3 (GLRaV-3) is a worldwide pathogen of Vitis negatively affecting wine production. In red berry cultivars grown in New Zealand, the foliar changes to GLRaV-3-infected vines inform decisions on vine removal (roguing). However, roguing does not always contain GLRaV-3 spread in the presence of an insect vector like the mealybug, Pseudococcus calceolariae. Virus incidence and mealybug abundance data collected annually over 7 years were modelled under differing scenarios to ascertain support for roguing. In a simulated 1 ha vineyard planted in 2500 mature Merlot vines, simulations over 20 years evaluated the effectiveness of roguing, ‘rogue 1 + 2’ (concurrent roguing of symptomatic plus both within-row neighbouring vines), inefficient roguing (50% of symptomatic vines rogued), and ‘no-action’. The model used variable initial GLRaV-3 incidence (0.4, 5, 10, 15 and 20%), and low, median and high vector densities (6, 26 and 75 mealybugs per 100 vine leaves, respectively). Roguing was the optimal response to GLRaV-3, independent of the initial incidence, but results were vector density dependent. At a low vector density, roguing relative to the other responses tested, sustained the lowest annual GLRaV-3 incidence, the least need to plant replacement vines and the lowest estimated average annual costs plus loss of income. At median and high vector densities, roguing remained the most favourable response but virus control was less effective and the costs incurred were higher. Thus, for vineyards affected by GLRaV-3, achieving economic sustainability relies on integrating efficient roguing with effective vector management.