Issue link: http://winesandvines.uberflip.com/i/62507
GRAPE GRO WING Is certified grapevine nursery stock really clean? Since the accidental introduction and spread of vine mealybug, grapevine nurseries have really improved their sanitation prac- tices. Following the huge planting boom of the 1990s, the nursery industry has had plenty of time to catch up and improve its brand. They are supportive of the UC Foundation Plant Service (FPS) Clean Grape Vine Nursery Stock program and concerned about unwittingly selling customers a potential problem—very bad for business in both the short and long term. Regardless, this remains a work in progress. There has been a huge sea of change in clones that are available for many varieties, and most nurseries are sourcing their wood from UC FPS. It is pretty doubtful that the leafroll virus problems that we are seeing develop in Napa vineyards are the result of planting virus-contaminated nursery stock. Most nurseries are reluctant to propagate grower field selec- tions unless they have some idea of the source of the wood and its virus status. Many nurseries are also testing their mother blocks to be certain that the vines are remaining virus free. In the coming year, the Na- tional Clean Plant Network will work with UC Foundation Plant Services to provide nearly $120,000 of free virus testing to grape- vine nurseries to help certify that their mother blocks are virus free. We used to make vineyard budwood selections from good vineyards and graft new vines with few problems. What has changed? Older rootstocks like AXR-1 and St. George were more tolerant of viruses and didn't show symptoms as readily as some of our newer rootstocks (particularly 3309C). There has also been a change in wine styles, with wineries rou- tinely asking for fruit above 25° Brix. Two decades ago, 23.5° Brix would have been adequate. Vines that had a small amount of leafroll could meet those standards, but it would be difficult to ripen to many wineries' more demanding ripeness goals, which are now fairly routine. If I have a clean, newly planted vineyard and my neighbor's vineyard has obvious leafroll issues, what can I do to prevent the spread of disease? This is the topic that UC researchers around the state are actively investigating. Besides the epidemiology work mentioned earlier in this article, mealybug control is a logical research topic since mealybugs are the principal vectors that spread leafroll viruses. Several different insecticides are quite effective at lowering vine mealybug numbers, especially Applaud (an insect growth regu- lator) and Movento (a systemic insecticide), both of which are relatively nontoxic. Two sprays per year could have a significant impact on reducing mealybugs and may very well limit the spread of leafroll virus from adjacent vineyards. For those interested in a pest management strategy more compatible with organic/biody- namic methods, pheromone dispensers could be used along with biocontrol agents. Two little wasp parasitoids look promising— Anagyrus pseudococci and Coccidoxenoides perminutus. To be effective, ants in the vineyard also must be controlled. In ongoing research trials, bait solutions containing boron and sugar water are looking effective for that purpose. Some vineyard owners claim that when they changed to organic and Biodynamic farming practices, their leafroll symptoms were lessened. Is this possible? While there are some grower testimonials about this, there is no scientific evidence to back up these claims. Improved soil condi- tions may have improved vine growth, which can help improve overall vine vigor. 62 Wines & Vines OCTOBeR 2011