Bois noir

Bois noir is a significant phytoplasma disease affecting grapevines, caused by Candidatus Phytoplasma solani. This systemic pathogen invades the plant's phloem, which disrupts the transport of carbohydrates and essential nutrients throughout the vine. The disease is a type of "grapevine yellows" and is considered one of the most economically damaging phytoplasmoses in European viticulture.

The primary host for this disease is the cultivated grapevine (Vitis vinifera). However, the phytoplasma also resides in various herbaceous plants, most notably field bindweed (Convolvulus arvensis) and stinging nettle (Urtica dioica). These weeds act as essential reservoirs, allowing the pathogen to persist in the environment even in the absence of grapevines.

Symptoms of Bois noir typically appear in mid-summer. Affected leaves curl downward and discolor, turning yellow in white varieties or reddish-purple in black varieties. Shoots fail to lignify properly, remaining green and flexible until late autumn, which often leads to severe winter damage. In addition, flower clusters may wither, and fruit set is poor, resulting in small, tasteless berries that are unfit for wine production.

The disease is transmitted by the planthopper Hyalesthes obsoletus. This insect acquires the phytoplasma while feeding on infected weeds and later transfers it to grapevines during its migration. The spread of the disease is heavily influenced by the presence of host weeds in and around the vineyard, which facilitate the life cycle of the vector and the transmission of the pathogen to the vines.

Management of Bois noir relies exclusively on preventive measures, as there is no chemical cure for infected vines. Integrated management strategies include:

• Rigorous control of reservoir weeds, particularly bindweed and nettle, to break the infection cycle.
• Monitoring and controlling the Hyalesthes obsoletus population using appropriate insecticides during peak migration periods.
• The use of clean, certified planting material to prevent the introduction of the pathogen into new vineyards.
• Prompt removal and destruction of heavily infected vines to reduce the inoculum pressure in the vineyard.