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Grapevine Yellows: Flavescence dorée and Bois noir Identification Guide
Grapevine Yellows: Flavescence dorée and Bois noir
Background
Grapevine yellows diseases caused by phytoplasmas are found in many areas of the world
where grapes are grown. Flavescence dorée (FD) and Bois
noir (BN) are two grapevine yellows diseases that are considered quarantine pests
in Canada because they can affect crop yields of affected grapevines. There are no human
health risks associated with these pests.
BN and FD are commonly found in several European countries. The first detection of one
of these pests in Canada was the confirmation of BN on a recently imported grapevine in
British Columbia during the Canadian Food Inspection Agencys 2006 routine
surveillance program. An investigation into this detection is underway.
Varietal Susceptibility
All Vitis vinifera varieties are susceptible to
phytoplasmas. Some of the most important varieties such as Chardonnay, Pinot blanc, Pinot
noir, Cabernet Sauvignon, Sauvignon blanc, Pinot gris and Sémillon are very sensitive,
whereas Merlot appears to be relatively tolerant. Plants infected with FD and BN may
recover, but symptoms may reoccur, sometimes years later. Vitis
labrusca and American rootstocks develop very weak symptoms or no symptoms at
all. However, if infected, they may act as phytoplasma reservoirs and facilitate disease
spread.
Symptoms
Grapevine yellows diseases all produce similar symptoms and many plant parts are
affected including fruit, growing points, leaves and canes. Plant growth may be stunted.
Grafting is often not successful and young grafted plants often die quickly. Usually a
combination of symptoms will develop on plants.
Disease Progress:
Symptoms may first appear in early summer and increase in incidence and severity until
harvest. Early season symptoms can be observed on the flowers and as undeveloped
flower/fruit bunches. Young shoots may have closely spaced branches and zig-zag growth (Figure 2) with some early leaf rolling. Subsequently, berries will shrivel
as peduncles dry. Leaf symptoms become more pronounced as the summer progresses, followed
by poor wood ripening that gives the vines a rubbery, weeping appearance.
Symptoms on newly infected plants may be restricted to a few shoots with more of the vine
becoming diseased with time.
Foliar Symptoms:
(Figure 1, 4)
- Leaves are discoloured, edges roll downward, leaf blade becomes brittle.
- Leaf rolling often results in an angular shape.
- Spots form on sun-exposed surfaces of the leaves, which enlarge into bands along the
veins. These will gradually cover the entire leaf surface.
- Colour of the spots and bands varies with the cultivar: white-fruited. varieties usually
have creamy-yellow spots and red-fruited cultivars have reddish spots.
- Leaves may overlap each other down a cane.
Flower and Fruit Symptoms:
(Figure 5)
- Flowers dry out and fruit will not set on initially infected plants.
- Bunches on plants that become infected later in the season will become brown and
shrivelled.
- Fruit will drop very easily on some varieties.
Cane Symptoms:
(Figure 3)
- Canes ripen poorly and unevenly, often showing green and brown sections along the cane.
- Canes with poorly ripened wood will appear rubbery, often causing a weeping
appearance.
- Poorly ripened wood will often blacken and die during the winter.
- Numerous small pustules may appear along diseased branches and longitudinal fissures may
appear in the bark at the base of badly diseased branches.
- Symptoms may be confused with Botrytis cinerea on canes
and stems.
Comparison of Phytoplasmas with Other Grapevine Diseases
Leaf-roll Diseases: Phytoplasma symptoms may be confused with
grapevine leaf-roll disease. Grapevine leaf-roll disease symptoms usually start on older
leaves and develop up the cane. Phytoplasma diseases are often first seen nearer the top
of the plant. Discoloration due to leaf-roll starts between the veins and the veins
usually remain green. Also, grapevine leaf-roll disease does not affect cane ripening and
fruit bunches do not shrivel.
Esca Disease: Withering of the bunches and leaf reddening may be
confused with Esca disease. However in the case of Esca, the stock will collapse suddenly
in July or August. Esca is caused by a complex of several fungi including Phellinus igniarius and Stereum hirsutum.
To report plants with suspected symptoms of FD and BN, please call the CFIA at
1 800 442-2342.
Photographs:
Dr. Michael Maixner
Federal Biological Centre for Agriculture and Forestry (BBA)
Institute for Plant Protection in Viticulture
Bernkastel-Kues, Germany
Examples of FD and BN Symptoms on Riesling
Figure 1: Foliar symptoms
(Click on image for larger view)
Figure 2: Early season short internodes
(Click on image for larger view)
Figure 3: Uneven wood ripening
(Click on image for larger view)
Examples of FD and BN Symptoms on Pinot Noir
Figure 4: Foliar symptoms
(Click on image for larger view)
Figure 5: Affected fruit
(Click on image for larger view)
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