Bois noir

Bois noir is a serious grapevine disease caused by the phytoplasma Candidatus Phytoplasma solani. Taxonomically, it belongs to the class Mollicutes and the family Acholeplasmataceae. These pathogens are wall-less bacteria that reside within the sieve tubes of the plant's phloem, interfering with the translocation of sugars and nutrients, which leads to the characteristic "grapevine yellows" syndrome.

The disease primarily affects grapevines (Vitis vinifera), but it also impacts various vegetable crops and common weeds like bindweed (Convolvulus arvensis). Symptoms are systemic and include chlorosis or reddening of leaves, downward curling of leaf blades, incomplete lignification of shoots, flower abortion, and shriveling of berries. In severe cases, the entire vine becomes stunted and may die within a few years.

The life cycle of the pathogen depends entirely on its insect vector, the planthopper Hyalesthes obsoletus. The phytoplasma persists in perennial weeds, with bindweed serving as a primary reservoir. The insects overwinter as nymphs on the roots of these weeds. During the spring, the adults emerge and migrate to grapevines, inoculating the healthy plants with the phytoplasma while feeding on the phloem sap.

Environmental conditions, particularly hot and dry weather, favor the movement and activity of the vectors, leading to increased incidence of the disease in vineyards. Bois noir usually spreads from edges adjacent to uncultivated areas or infested fields. Because the infection is systemic and colonizes the vascular system, there is no chemical cure for an infected vine, making preventative measures the only effective strategy.

Management and control strategies include:

• Maintaining clean cultivation by eradicating reservoir weeds like bindweed in and around the vineyard.
• Implementing insect monitoring using yellow sticky traps to track the population dynamics of Hyalesthes obsoletus.
• Applying targeted insecticide treatments during the peak emergence period of the adult planthoppers.
• Rouging out and burning severely infected vines to eliminate sources of inoculum.
• Selecting high-quality, certified nursery stock to prevent introducing the pathogen into new plantings.