For the history and the description of the various diseases and pests attacking grapevine, specialized works can be consulted. However, we will quickly review the diseases and pests that are currently most feared by wine growers.
POWDERY MILDEW (OIDIUM)
It is the first disease of American origin introduced in Europe, so it was at that time “the disease of grapevine”. It was identified for the first time in 1945 in greenhouses in south-east England, and in 1951 it was reported in Podensac in Gironde, France.
Powdery mildew is due to a fungus, Uncinula necator which reaches all the non-lignified organs of the vine. Winter conservation of the fungus in the buds leads to the appearance of young powdery shoots in spring called “flags”. The fungus is capable of destroying partially or almost totally the crop, first by early attacks which cause ”vine sag” , then also by the destruction of the berries. Sulfur was the first substance used to control powdery mildew. Nowadays, the control is preventive, and different possibilities of biological control have been recommended to be deployed before the first signs of an epidemic. Considering the aggressiveness of powdery mildew on the bunches of grapes, an efficient and long-term protection must be carried out, especially from the pre-flowering stage to the closing of the bunch.
DOWNY MILDEW
Downy mildew is a disease caused by the oomycete Plasmopara viticola, originating from North America. It was identified for the first time in 1878 in the vicinity of Coutras, France and has caused considerable damage since then. It attacks all the non-lignified organs of the vine: leaves, young shoots, bunches and grains. In spite of the discovery in 1885 of copper-based treatments, this disease often take the wine growers unprepared and may cause very important damages.
Currently, the damage caused by downy mildew is low, with the exception of periods of particularly hot and humid climate, which is very favorable to its development.
Current control strategies against mildew are numerous and quite efficient. Nevertheless, control remains preventive and depend on the action modes of fungicides. The use of curative treatments must be reserved to exceptional situations, such as when an epidemic was not anticipated or the impossibility, for weather reasons to apply a preventive treatment.
ROTS DUE TO BOTRYTIS CINEREA
Botrytis cinerea is a fungus present worldwide that can attack a large number of plants species as soon as the environmental and host conditions are favorable.
Depending on weather and vine cultivation conditions, B. cinerea can cause grey rot or common rot, which are much dreaded by grapevine growers, but it is also responsible for noble rot, a much milder fungal attack which is sometimes desired to produce rare (and expensive) sweet wines.
Grey rot can, in certain humid years, cause considerable damage to both white and red vineyards. The disease incidence is higher nowadays, exacerbated by vigorous rootstocks and important fertilization that increase the vigor of the plant.
It attacks all the herbaceous organs of the vine, but causes the most considerable quantitative and qualitative losses of harvest, when the pre-harvest season is rainy. This disease is favored by other fungi (Powdery mildew) and by grape worms. The control of grey rot begins with the implementation of prophylactic measures (reduction of vigor, control of grape worms, green work…). Protection is based on the application of four treatments at specific phenological stages. Highly efficient active molecules allow the deployment of a reasoned protection in which two treatments only are recommended: the first one at the end of flowering, the second one at fruit-ripening. The latest risk-forecasting models allow to further reduce the number of interventions.
In the case of noble rot, B. cinerea attacks overripe, healthy and intact grapes. It concentrates the sugars in the berry, which decreases in volume while the skin turns brown and is covered with the gray fruiting bodies of the fungus.
EXCORIOSE
This disease is probably of European origin, but its damages have long been confused with those of anthracnose. The fungus Phomopsis viticola, particularly attacks growing branches, inducing brownish spindle-shaped necroses at their base or more extensive brown lesions. The shoot becomes brittle and may break under the action of wind or any rubbing, especially when bending the future fruit-bearing shoots after pruning.
This disease can also attack the stalk, causing the partial or total drying of the bunch. Specific treatments are carried out in spring at the beginning of the budding.
BLACK-ROT
This disease is also due to a fungus, Guignardia bidwellii, which was introduced around 1886 from North America. The damages caused by black-rot have diminished in importance following the generalization of treatments with copper compounds used against mildew.
But since 1945-1950, black-rot is on the rise again, perhaps as a result of the substitution of organic or organo-copper products for copper sulfate to control mildew. Thus, in some years (1952 for example), it caused important damages in Gironde, France. Like mildew, it attacks all the green parts of the plant: leaves, bunches, grapes, the branches being however not very sensitive. Black-rot is mainly a disease of the berries which are affected after the fruit set with characteristic symptoms. It can be controlled with the same active compounds as for downy mildew.
ANTHRACNOSIS
It is a disease of European origin, known since antiquity.
Anthracnose is caused by a fungus, Elsinoe ampelina. Before the arrival of powdery mildew and downy mildew in Europe, it was the most damaging disease in vineyards, because it attacks all the herbaceous organs of the vine. After the introduction of “Bordeaux mixture” in 1885, the incidence of the disease was considerably reduced. Nowadays, the fungicides used to control powdery and downy mildew make anthracnose an almost unknown disease in France. It is sometimes possible to observe it on some hybrids in Armagnac, France.
EUTYPIOSIS
Identified in 1974, this disease is caused by a lignicolous fungus, Eutypa lata, which develops in the trunk and arms of the stump causing a progressive decline leading to the death of the plant. The pathogen enters through pruning wounds. It is a very insidious disease which takes several years (6-7 years) before it manifests itself.
Some grape varieties (Cabernet Sauvignon) are more susceptible than others (Merlot noir).
The control of eutypiosis is for the moment preventive and consists in protecting the wounds at the time of the pruning. Fungicides are used either by brush spraying, by buffer-applicator, or by means of a pneumatic pruning shears spray. Prophylaxis consisting of eliminating dead stumps carrying the infectious form of the fungus remains the most efficient method in the long term.
ESCA OR APOPLEXY
It is the oldest disease described on vine. Several wood-eating fungi divided into two parasitic sequences (pioneer fungi: Eutypa lata, Phaeomoniella chlamydospora, Phaeoacremonium aleophilum; and secondary fungi: Formitiporia mediterranea and Stereum hirsutum) are involved in the esca syndrome. With the exception of Ph. aleophilum, these fungi penetrate through pruning wounds.
The disease manifests itself by a localized drying of the leaves between the veins, or by an apoplexy. The wood of the trunk is degraded, resulting in a white necrosis of soft consistency.
The control of Esca is prophylactic only since the banning of sodium arsenite at the end of 2001.
BLACK DEAD ARM
Identified in 1999 for the first time in French vineyards, Black Dead Arm was confused with Esca due to a similar symptomatology in the herbaceous vegetation.
Two fungi belonging to the Botryosphaeriaceae family are associated with this disease. Its emergence is probably linked to the reduction and then the cessation of sodium arsenite treatments.
On the trunk, symptoms consist in a brown band under the bark and a brown-gray to brown-black sectorial necrosis. Apart from the implementation of prophylaxis (removal of dead wood and pruning), there is no control method yet.
