Esca or Black Measles

What are the symptoms and consequences of ESCA in the vineyard?

The "tiger-stripe" leaf symptoms that characterize Esca's slow form appear around véraison and regularly during the entire growth period. They affect either the whole vine, or a single arm, or a few branches. The leaves on the lower part are affected first. It is important to note the extreme variability of the expression of the symptoms from one year to the next. A diseased vine one year may very well appear healthy the next year.
In white grape varieties, leaf symptoms are characterized by the presence of small, milky yellow spots, on the leaves' surface, and necrotic spots delimited by a milky yellow border, most often at the edge of the leaf.

Esca on Cabernet Sauvignon (Source: Vigne Vin Occitanie)

At more advanced stages, necroses are larger, leaving only a green band along the main veins, which gives the leaves a tiger-stripe appearance.
In black grape varieties, the same symptoms are observed with the difference that light red spots are also present on the leaf surface. They also surround all the necrotic areas and are separated from the green tissue by a milky yellow border.
Symptoms for the fruit can be delayed ripening or wilting. Fruit may also develop purplish-brown spots on their surface. These symptoms may or may not be associated with leaf symptoms. This facies, called Black Measles, is found in France, particularly in Alsace.

Esca symptoms on bunches

Esca is characterized by a white rot on the wood commonly called tinder fungus. This crumbly, light-coloured wood is caused by basidiomycetes fungi which have the particularity of developing from necroses caused by other fungi. These necroses, either in a central position or in a sectorial position, very often begin with pruning wounds.

What other diseases could it be confused with?

Several criteria can be used to distinguish between the slow form of Esca and Black Dead Arm:

Symptom emergence dates: the first symptoms appear from flowering onwards for Black Dead Arm whereas for Esca, they only appear around véraison.
The intensity of the colours of the spots on leaves: for white grape varieties, a bright yellow can indicate BDA whereas for Esca it is whitish. For black grape varieties, there is no yellowing on the leaves and the red is much darker for BDA. This distinction is difficult to make from véraison onwards because the tissues lighten. The vinous red becomes a light red and the green becomes tinged with light yellow.

With regard to the apoplectic form, it is not possible to distinguish between them without cutting the vines. This form of expression is not disease-specific. It affects individual vines in mid-summer, bearing fruit that withers within a few days. This form is often confused with the severe form of Black Dead Arm which, unlike Esca, results in defoliation of the branches before they dry out. It can also be confused with desiccation caused by other diseases such as root rot, eutypiosis, etc. or by more physiological problems such as strangulation of the rootstock, or very poor pruning. Apoplexy is observed in certain weather conditions, particularly during periods of drought or strong wind. The excessive evapotranspiration during these periods is no longer compensated by a sufficient influx of water, as only a small proportion of functional wood remains.

What fungi are associated with Esca?

Characterized by the presence of white rot (tinder) in the wood and the decline of the rootstock, going as far as apoplexy, Esca involves several types of fungi:

Phaeomoniella chlamydospora and Phaeoacremonium minimum, developing in a central brown necrosis
Eutypa lata (eutypiosis agent) responsible for brown necrosis in sectorial positions
Basidiomycetes fungi of which the most frequently encountered in France is Fomitiporia mediterranea. These fungi colonize the necroses caused by the above-mentioned fungi.

What is the biology of the micro-organisms that cause Esca?

The fungi are preserved on diseased or dead vines, but other wood species can also harbour them. Phaeoacremonium minimum spores seem to be spread during the growth period, whereas Phaeomoniella chlamydospora and Eutypa lata are spread all year round. Contamination occurs in particular through pruning wounds during mild and rainy periods.

The above questions are extracts from Vigne Vin Occitanie.

Are there any preventive measures?

There is no specific curative treatment for Esca. However, several prophylactic methods can be implemented from the initial planting that can reduce contamination by Phaeomoniella chlamydospora, Eutypa lata and Fomitiporia mediterranea fungi:

Vigour management: excessive vigour can favour the disease's establishment. Limiting vineyard vigour requires a thorough analysis of the plant material from the time of planting. Vineyard management must also be adjusted accordingly: debudding operations help reduce excessive loads. Any fertilization must also be carefully calculated. An excess of nitrogen can encourage excess vigour.
Vineyard cleanliness and hygiene: it is crucial to remove dead stumps from the plot which could constitute an infectious source of disease.
Pruning management: during winter pruning, if possible pruning wounds should be minimized. Leave a drying cone of several millimetres during the winter pruning. Remove a part of this cone by cutting it back the following year to reduce the presence of dead wood.
Protection following winter pruning: in organic winegrowing, it is possible to use approved Trichoderma-based products to protect pruning wounds against ESCA and BDA.

What techniques are available?

When a vine is affected by Esca, it is possible to avoid uprooting and to rehabilitate it. Several practices exist such as cutting back and regrafting. Curettage is a "surgical" technique which consists of opening the diseased vines in order to expose any tissue damaged by the fungi responsible Esca and removing it with a chainsaw.

Château Latour has been using the curettage technique for several years. Symptomatic vines were tagged with a GPS position in 2016 for curettage in 2017. Rigorous monitoring every year enables us to verify the success rate of the curettage, i.e. to identify the number of curetted vines not showing any symptoms of infection for at least two years after the curettage. The success rate was 85% after the first year. However, this is a time-consuming and technically demanding practice that would be difficult to extend to an entire vineyard.

Curettage (removal of dead wood) at Château Latour

2.4.2.b Esca or Black Measles