What we need to learn in order to make effective management decisions that target grapevine viruses Rhonda Smith Viticulture Farm Advisor Sonoma County

Grower concerns… Learning to live with this is critical; a lot of young vines have red blotch disease A 2-5% increase in diseased vines a year is a fire Grapevine nurseries each handle millions of plant units each year Why is it that rootstocks are far less infected than scion wood? Zero tolerance for viruses that negatively impact fruit quality

Management practices for leafroll disease Manage all stressors Nutrients Water Nematodes phylloxera Crop level HOPE for an early and long season Manage mealybugs

Management practices for red blotch disease Managing stressors?? Managing an unknown vector

Grower concerns about a vector What is it? Should I apply insecticides to reduce potential vector populations now? Is there a spatial relationship with block location and incidence of infection?

“Knowledge about the spatial distribution of infected plants at a given date may help in understanding whether or not the infection was already present in nursery plants, whether the virus was vectored from neighbouring vineyards, whether there was field transmission within a plot, and which factors favour spread of the infection.” Cabaleiro, C., & Segura, A Plant Disease, 81, 283–287. Madden, L. V., et.al Phytopathology, 77(10), 1409–1417. Maixner, M., & Reinert, W Extended abstracts 12th Meeting ICVG, Lisbon, Portugal, 29 September–2 October 1997, 75–76.

Understanding the characteristics of the epidemiology of GLRaV-3 in order to better understand the economic impact based in the different stages of GLRaV-3 in the field, so that growers can make better management decisions in the future. Understanding reinfection rates in terms of leafroll 3 for newly established blocks and blocks that are currently being rogued for leafroll 3. Kari Arnold, QBE Lab. Department of Plant Pathology, UC Davis

“Study of the changes in the spatial distribution during a suitably long period allows validation of the hypotheses and predictions made in accordance with temporal epidemiological models.” Madden, L. V. 2006). European Journal of Plant Pathology, 115, 3–23.

Sampling challenges A vector’s relationship with the virus is key to understanding Subsequent distribution patterns Rate of spread Vector management What determines the sample size? If not zero tolerance, what is the tolerance for leafroll disease in areas with mealybug for sustainable management? If not zero tolerance, what is the tolerance for red blotch disease for sustainable management?

Determine an accurate, efficient strategy to map diseased vines in commercial blocks Determine an accurate, and affordable testing method to determine diseased vines in commercial blocks and nursery increase blocks

Variable symptom expression Cultivar Site Vine capacity and vigor Year

Range of concerns among growers and winemakers Blocks have tested positive for red blotch virus, yet fruit and wine quality is excellent // not a problem When a block ripens a little slower than it ‘should’, will that block eventually become a liability in future years?

Informed grape growing and winemaking Determine effect of red blotch disease on fruit development and grape composition Determine the effects of red blotch disease on the non-volatile composition of fruit, including anthocyanins, flavonoids and non-flavonoid polyphenols

Informed grape growing and winemaking (continued) Comparison of singlet infections of GRBaV and GLRaV-3 to study the differences in the impact on juice parameters. Determine effect of GRBaV infection on wine quality parameters from vineyards of same cultivar and rootstock in different winegrape regions Mysore Sudarshana, USDA, UC Davis