Grapevine yellows

Click to enlarge.

Beginner

Scientific Names
North American Grapevine Yellows: Flavescence Dorée, Bois Noir, Aster Yellows, X-disease

Identification
Infected grapevines usually show symptoms a few months to 1 year after infection. In some cultivars, symptoms can appear a few years after the infection. Symptomless plants can be infected.

Leaves

Roll downward in spring
Mid-summer, leaf rolling increases
Leaves become brittle and turn golden yellow (white cultivars) or red (red cultivars)
Yellowing or reddening starts as spots on sun-exposed surfaces, then enlarge into bands along the veins and gradually cover the entire leaf surface
Diseased leaves tend to fall later in the fall

Shoots

Bud break and initial shoot growth of infected vines may be retarded or occur erratically
Remain short in spring
Mid-summer shoots exhibit total or partial absence of lignification, giving shoots a drooping habit
Numerous small black pustules may appear at the base of shoots

Fruits and inflorescences

If symptoms appear early, inflorescences dry out and fruit set is reduced
If symptoms appear late in the season, the fruit bunches become brown and shriveled
Premature berry drop occurs in some cultivars

Often Confused With:
Grapevine Leafroll Virus: no swollen internodes or “weeping posture” of shoots

Potato leafhopper: no swollen internodes or “weeping posture” of shoots; presence of nymphs, adults and cast skins

Potassium/magnesium deficiency: no swollen internodes or “weeping posture” of shoots

Crown gall- incomplete periderm development and cluster abortion do not occur; galls on trunk

Period of Activity
Maximum spread occurs from mid August through October when high concentrations of the pathogen are present in the leaves and vector populations are increasing in orchards and vineyards.

Scouting Notes
The best time to observe symptoms is mid-summer, before foliar colour change in fall. Grapevine yellows-infected vines are easy to spot when yellow and red colour of symptomatic leaves appear.

Threshold
Flavescence dorée and Bois noir are quarantinable diseases so no level of infection is acceptable.

Advanced

Scientific Names
North American Grapevine Yellows (NAGY): Flavescence Dorée (FD), Bois Noir (BN), Aster Yellows (AY)

Leaves

Roll downward in spring
Mid-summer, leaf rolling increases
Leaves become brittle and turn golden yellow (white cultivars) or red (red cultivars)
Yellowing or reddening starts as spots on sun-exposed surfaces, then enlarge into bands along the veins and gradually cover the entire leaf surface
Diseased leaves tend to fall later in the fall

Shoots

Bud break and initial shoot growth of infected vines may be retarded or occur erratically
Remain short in spring
Mid-summer shoots exhibit total or partial absence of lignification, giving shoots a drooping habit
Numerous small black pustules may appear at the base of shoots

Fruits and inflorescences

If symptoms appear early, inflorescences dry out and fruit set is reduced
if symptoms appear late in the season, the fruit bunches become brown and shriveled
Premature berry drop occurs in some cultivars

Often Confused With:
Grapevine Leafroll Virus: no swollen internodes or “weeping posture” of shoots

Potato leafhopper: no swollen internodes or “weeping posture” of shoots; presence of nymphs, adults and cast skins

Potassium/magnesium deficiency: no swollen internodes or “weeping posture” of shoots

Crown gall- incomplete periderm development and cluster abortion do not occur; galls on trunk

Biology
Flavescence Dorée has not been detected in Canada. Bois Noir was detected in B.C. and eradicated. North American Grapevine Yellows has not been detected in Canada but both of the component phytoplasmas of this disease, Aster Yellows and X-disease of stone fruit, are present.

Flavescence Dorée is spread by the leafhopper Scaphoideus titanus, which is native to eastern North America. Flavescence Dorée phytoplasma and viruliferous S. titanus can be spread by contaminated propagation materials. S. titanus is also known to transmit Aster yellows phytoplasma through feeding.

Bois noir is transmitted by Hyalesthes obsoletus, an insect that is not present in Canada. It is widespread in many parts of Europe and is now the second most important grapevine yellows disease after Flavescence Dorée. Recent identification of potential Bois Noir vectors as well as associations between Bois Noir strains and weed species in Europe, have raised concern in Canada. Bois Noir transmission by plant propagation is low.

North American Grapevine Yellows is caused by a co-infection of Aster Yellows and X-Disease phytoplasmas. Aster Yellows commonly infects many weeds in Ontario and X-disease has been found in cultivated peach orchards as well as wild chokecherry here. Movement of X-disease can occur from infected sweet and sour cherry, although chokecherry is often the principle reservoir. Other reservoirs of X-disease include certain weeds such as clover, dandelion, and several rosaceous species including strawberry and blackberry.

Potential Aster Yellows vectors have been identified in Canada, but their ability to vector phytoplasmas remains to be confirmed. Differences in Aster Yellows susceptibility among grape varieties have been observed. Both aster leafhoppers and Aster Yellows phytoplasma have a wide range of host plants, including many broadleaf weeds, grains and grasses

Threshold
Flavescence dorée and Bois noir are quarantinable diseases so no level of infection is acceptable.

Management Notes
Symptoms can be easily confused among phytoplasmas, viruses and nutritional or environmental effects. The only accurate way to diagnose phytoplasmas is by tissue samples analyzed at a qualified lab. Consultants or extension specialists can help with accurate diagnosis.

Use only vines produced from scionwood and rootstock material obtained through a clean stock or certification program.

Remove and discard infected vines..

GRapes

Grapevine yellows

Beginner

Advanced