When leafroll virus strikes a vineyard, growers may not always be able to rip out infected plants and replant with healthy ones because of winery contractual arrangements or finances.
Although the virus poses no threat to food safety, it can create challenges for vintners unless they approach grapes from infected vines a bit differently, according to a news release.
Washignton State University enologist Jim Harbertson spent three years experimenting with making wines from grapes from leafroll-infected vines. He worked alongside leafroll virus expert Naidu Rayapati.
The most noticeable symptoms are reductions in berry color, Brix and yield. Color reduction isn't as pronounced in hot growing areas compared to cooler ones. At the same time, hot areas may produce fruit with lower acid levels.
For red wines, the simplest solution is more skin contact time and more extraction time at the winery, Harbertson says.
Tannins can be bolstered by using pomace from a previous fermentation or by adding bagged tannins within legal limits.
In white wines, problems caused by leafroll virus typically are not as severe, since reduced acidity and Brix may actaully be desirable.
But the potential loss of ripening characteristics, such as volatiles, that give white wines their distinct aromas could be troublesome.
Little or no research has been conducted in this area, Harbertson says, and further study, especially on aroma compounds, is needed.
Regardless of the variety, he says it's paramount to identify infected plants in the vineyard and keep records of them.
For more information on leafroll virus, download Rayapati's Extension publication, Grapevine Leafroll Disease.”.