The fungus that causes black rot of grapes (Guignardia bidwellii) threatens all green parts of the grape. This pathogen can cause great damage to vines and reduce yields by up to 60-80% in warm and wet weather conditions. It was first detected in Hungary in 1999.

The phylogenetic classification of the fungus causing black rot is the same as that of the fungus causing powdery mildew of grapes (Erysiphe necator), both are Ascomycota.
Overwintering of the fungus can occur in sexual and asexual forms, as well as in the form of fungal filaments in plant parts. Sexual overwintering occurs with pseudothecia, yet asexual overwintering occurs with pycnidia.

Fungal overwintering can occur in fallen leaves, the base of canes, buds and ducks, but also in the support system and soil. However, the most important source of infection is the crushed, mummified berries previously left on the stalks or fallen on the ground, which must be removed from the area and not turned into the soil.

In spring, the release of asexual conidia usually starts at the time of flower bud break, while that of sexual ascospores starts about two weeks later, but the greatest mass dispersal of spores is expected between mid-flowering and pea size.

The overwintering formulas of this fungus are highly resistant. They retain their viability and infectivity for at least two years, so that the overwintering fungal formations are capable of causing infections in the following year.

Mechanical methods of control are of particular importance compared to the powdery mildew and peronospora diseases discussed earlier, while chemical treatments are more curative.

Máté Havasi
plant health specialist
PlantCT Europe Zrt.