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
• Manage all stressors
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. 1997. Plant Disease, 81, 283–287.
Madden, L. V., et.al. 1987. Phytopathology, 77(10), 1409–1417.
Maixner, M., & Reinert, W. 1997. 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, 2014. 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
• 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
• 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
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


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