What diseases truly threaten grapevines throughout the season? Between fungi, bacteria, and disorders that weaken foliage, grapes, or wood, it’s not always easy to distinguish between them in the field. However, accurately identifying the symptoms, the timing of their appearance, and the affected organs allows for more targeted action. Agrobiotop helps you identify the various problems and offers natural solutions for viticulture , drawing on its expertise in agrobiology.
Grape downy mildew
Grape downy mildew (Plasmopara viticola) develops primarily during periods of heavy rain combined with high humidity and temperatures between 11 and 30°C. It manifests as oily, yellowish spots on the leaves, accompanied by a white downy coating on the underside, followed by progressive necrosis; the grape clusters may turn brown or dry out, particularly around flowering and fruit set. The pathogen overwinters in plant debris and restarts its life cycle in the spring, leading to successive infections.
Powdery mildew of grape
Powdery mildew of the grape ( Erysiphe necator ) often appears in conditions of high humidity and low light, with favorable temperatures between 20 and 30°C. It is recognizable by its powdery, greyish-white coating on leaves and bunches, causing deformation, stunted growth, and berry splitting. The fungus can overwinter in buds or as specific structures on shoots, which explains why infections occur early.
Do you need expertise and solutions for your vineyards?
Black-rot
Black rot, also known as black rot of the vine, is caused by Guignardia bidwellii . The leaves develop brown spots bordered by a dark edge with characteristic black dots, while the berries rapidly develop a rough, black mummification. The disease is active from bud break to veraison, with young shoots being particularly susceptible.
Grey mold (Botrytis)
Gray mold of the vine is a fungal disease caused by Botrytis cinerea , linked to high humidity and moderate temperatures. It often develops on weakened or damaged tissues, particularly after powdery mildew attacks or severe weather events. It causes browning of the berries followed by a dense gray mold that spreads rapidly within the bunch. The fungus can remain dormant from flowering onwards and become active at veraison or before harvest.
Golden flavescence
Golden flavescence is a regulated grapevine yellows disease caused by the bacterium Candidatus phytoplasma vitis and transmitted by a specific insect vector, with major economic consequences. Leaves become rigid, curl, and change color, while grape clusters dry out and shoots fail to lignify properly. Symptoms often appear the year after infection, making visual diagnosis difficult.
Black wood
Black wood, also known as stolbur of the vine, presents symptoms very similar to those of flavescence dorée, with yellowing or reddening of the foliage and drying of the grape bunches. It is caused by a phytoplasma transmitted by the leafhopper Hyalesthes obsoletus on reservoir plants such as bindweed or nettle. The grapevine generally provides a dead end for the spread of the disease, which limits direct contamination between vines.
Grapevine esca disease
Esca is a fungal disease caused by a complex of fungi ( Phaeoacremonium aleophilium, Phaeomoniella chlamydospora, and Eutypa lata ) that affects the wood, with varying degrees of severity from year to year. The leaves develop characteristic mottling, while the inner wood shows necrotic or spongy areas. In some cases, the vine can die suddenly. The disease often enters through pruning wounds and progresses slowly, with periods of dormancy.
Eutypa dieback of grapevine
Eutypa dieback ( Eutypa lata ) is a grapevine trunk disease that develops from infections on pruning wounds, particularly in humid conditions. It leads to a progressive weakening of the vine, with short shoots and deformed foliage. The wood shows well-defined necrotic lesions, visible when cut. The progression is slow, sometimes over several years, making early detection difficult.
Phomopsis cane spot
Phomopsis cane spot, caused by Phomopsis viticola , primarily affects young shoots in spring, linked to humid conditions after budbreak. It manifests as elongated, dark lesions on the first internodes, which can develop into cracks and cankers. Grape clusters can be affected via the peduncles, leading to localized losses. The disease overwinters in infected shoots, highlighting the importance of rigorous vineyard cleaning and early monitoring.
Grapevine fanleaf disease
Fanleaf virus is a viral disease transmitted by soil nematodes, with a long and difficult-to-control persistence. Observed symptoms include leaf deformities, abnormal shoot growth, and a significant yield reduction due to fruit drop and shot berries. The virus can survive in the roots and vectors for several years.
Bacterial necrosis of grapevine
Bacterial necrosis of grapevine, caused by Xylophilus ampelinus , develops in humid conditions, often from contaminated material or wounds. It affects the vascular system, causing various symptoms: leaf spots, localized dieback, abnormal bud break, and deep lesions on shoots. Diagnosis can be confused with other diseases, hence the importance of laboratory confirmation.
Other grapevine tips
Photo : Shutterstock
