Grapevine Yellows: Schwarzholzkrankheit & Goldgelbe Vergilbung

• These notes are about grapevine yellows diseases, specifically Schwarzholzkrankheit (Bois noir) and Goldgelbe Vergilbung (Flavescence dorée)
• These are viral diseases affecting grapevines

Key Points

• Goldgelbe Vergilbung, if unmanaged, leads to significant yield losses in grapevines
• Grapevine yellows diseases are caused by phytoplasmas (bacteria lacking cell walls)
• Schwarzholzkrankheit has been increasingly present in South Tyrol since the late 1990s
• The first suspected case of Goldgelbe Vergilbung was confirmed in autumn 2016

Grape Varietal Susceptibility

• Very High: Chardonnay, Zweigelt
• High: Kerner, Müller Thurgau, Riesling
• Medium: Burgundy varieties, Gewürztraminer, Goldmuskateller, Lagrein
• Low: Cabernet, Grüner Veltliner, Merlot, Sauvignon blanc, Silvaner, Vernatsch

Disease Symptoms

• Both diseases cause similar symptoms
• Distinguishing between the diseases requires molecular biological investigations
• Symptoms are most evident from the start of ripening
• Leaves roll downwards creating a triangular shape
• White grape varieties will develop yellowish leaves
• Red grape varieties will develop reddish leaves
• Leaves become brittle and make a metallic rustling sound when crushed
• Shoots often fail to or only partially lignify, appearing rubbery and exhibiting a zigzag growth pattern
• Black, oily pustules present on shoots
• Flower clusters die off after blooming and dry out
• Late-season symptoms include shriveled, unripe, bitter berries, unsuitable for winemaking

Monitoring of Grapevine Yellows Diseases

• The Plant Protection Service of the Autonomous Province of Bozen-South Tyrol, in collaboration with the Laimburg Research Centre and the South Tyrolean Advisory Ring for Fruit and Winegrowing, monitors grapevine yellows diseases in all wine-growing areas of the region
• Reporting suspected cases is mandatory, free, and doesn't lead to negative consequences
• Laboratory analysis is conducted after samples are taken from suspected cases
• Owners are informed in writing if a sample tests positive

Disease Spread

• Schwarzholzkrankheit spreads slowly through various host plants and is localized
• Goldgelbe Vergilbung spreads rapidly from vine to vine, and is considered a quarantine disease

Disease Vectors

• Schwarzholzkrankheit is spread by the bindweed planthopper (Hyalesthes obsoletus)
• Larval development occurs in the soil, and they feed on the roots of host plants
• Adults are capable of flight and appear from mid-May, laying eggs near the roots of new host plants for the next generation
• Overwintering occurs as larvae in deeper soil layers
• Goldgelbe Vergilbung is spread by the American grapevine leafhopper (Scaphoideus titanus)
• It produces one generation per year and overwinters as eggs in the bark of one- and two-year-old wood
• Adults are highly mobile
• The leafhoppers can transmit the pathogen after feeding on infected plants, remaining infectious for life

Risk Factors

• Schwarzholzkrankheit is linked to a high presence of nettles (Urtica ssp.), field bindweed (Convululus arvensis), and hedge bindweed (Calystegia sepium)
• Year-round herbicide use promotes the growth of bindweed and nettles
• For Goldgelbe Vergilbung, the entire life cycle of Scaphoideus titanus occurs on the grapevine, making infected vines a high risk

Control Measures

• Do not mow or remove the host plants during the insect's flight period (mid-June to late July)
• Remove shoot sprouts as early as possible
• Schwarzholzkrankheit warrants the treatment of nettles and bindweed in the soil
• For transplanting, use plant tubes for re-planting
• Remove and destroy vines, including rootstock that show disease symptoms
• Goldgelbe Vergilbung is mandatory to control

Vector Management

• No control is necessary for Schwarzholzkrankheit.
• The control of Goldgelbe Vergilbung is mandatory.
• According to Ministerial Decree of May 31, 2000, vector and disease presence requires mandatory insecticide treatment by the plant protection service.