2.4.1.e Phomopsis dieback or excoriosis

What are the symptoms of excoriosis on shoots in the spring and summer?

Excoriosis is a vine disease caused by the fungus Phomopsis viticola. In the spring, affected vines (usually on the first 3 internodes) may develop black punctiform or elongated spots around 15 days after budburst.
Over the course of the summer, the spots evolve into brownish necroses, black crusts or extensive brown lesions with perpendicular striations with a corky appearance ("chocolate bar" facies). In cases of severe outbreaks, the leaves may show round spots that dry up and fall off.
The foliage then takes on a leaden appearance. The fungus can also sometimes attack the berries. This phenomenon is quite frequent in the USA but is relatively uncommon in France. Branches affected by excoriosis are weakened and can break, which can lead to a significant loss of yield, especially with short pruning techniques with only two buds.

What are the symptoms of excoriosis on shoots in the autumn, winter and following spring?

Any necrosis previously observed during the spring will remain visible on the lignified shoots. In severe attacks on the basal section of the shoots, strangulation may also be observed where the two-year-old wood joins the vine. Occasional white discolourations with small black spots (pycnidia) may sometimes be observed on the first internodes of an affected shoot. In the winter, the pycnidia release pale yellow cords containing pycniospores. The following spring, around budburst, some shoots may even die back.

Extract from Vigne Vin Occitanie.

What are the symptoms of excoriosis on leaves and clusters?

Phomopsis dieback can also produce symptoms on the leaves and grape clusters. When attacks are severe, small round and irregular brown and black spots can appear. The leaves then appear as if riddled with lead.

The fungus can also be symptomatic in the bunches, but this remains rare, especially in France. They then become brown-purple, shrivel and fall.

Is it possible to confuse these symptoms with another disease?

Is it possible to confuse these symptoms with another disease?

What is the biology of the fungus?

The excoriosis fungus (Phomopsis viticola) spends winter as mycelia and pycnidia on the bark and solely as mycelia on dormant buds. It produces black pycnidia in late winter and spring on excoriated wood. When the weather conditions become favourable for pycnidia germination (prolonged rain), they emit a yellow cord containing the pycniospores.
The rain, by diluting these cords and spores, enables their dissemination to receptive organs where they germinate if there is a prolonged damp period. This dispersal takes place over short distances and the disease remains very localized. Contaminated plant material, on the other hand, is a source of long-distance dissemination. The vine has a very short period of receptivity between stages D and E according to the Baggiolini stages.
It should be noted that it is quite easy to diagnose excoriosis by placing a fragment of an affected shoot in a humid chamber for a few days. The pycnidia will release the cords containing the pycniospores after 24 to 48 hours.

Extract from Vigne Vin Occitanie.

What are the practices that favour excoriosis? What are the preventive measures?

Certain practices can favour phomopsis dieback establishment and development:

• Plant material selection: some grape varieties are more sensitive than others to phomopsis dieback, such as Cabernet Sauvignon, Folle Blanche, Merlot or Sauvignon. Prophylactic solutions: Other varietals demonstrate better tolerance to this disease, such as Pinot Meunier, Carignan and Cinsault.

• Vigour management: vigorous and dense vines facilitate a humid microclimate with higher risks of contamination by the fungus responsible for phomopsis dieback. When grass cover is poorly controlled, it can maintain a humid microclimate in close proximity to the vines, as can poorly adapted nitrogen fertilization. Prophylactic solutions: Control the vines' vigour (grassing, nitrogen fertilization, etc.) to avoid encouraging the development of the disease.

• Vineyard management: following the same reasoning as above, the microclimate is likely to present high humidity in the case of a lack of or inappropriate execution of certain green operations such as debudding, thinning, and leaf removal. When plants are affected within a plot, if the diseased branches (containing pycnidia) are not removed, this constitutes a form of dissemination of the disease. Prophylactic solutions: Eliminate affected branches during pruning and remove them from the plot while also adapting the canopy management schedule to suit vigour characteristics.

• Treatment management: an absence of preventive treatments when weather conditions have been favourable in previous years or in the current year to the establishment and proliferation of the disease can increase the risk of contamination. Prophylactic solutions: Preventive treatment during early phenological stages if the disease was present in previous years.

At what stage of the vines' development should treatment be started?

Control of phomopsis dieback in the vineyard depends on the plot's history and is solely chemical. In organic agriculture, only sulphur is authorized, usually in the form of dispersible granules.

Treatments must be carried out on a preventive basis during the vine's most sensitive phase, between the D and E stages. If symptoms are observed during pruning, then a protective treatment should be considered, unless the weather forecast is for very dry weather.

Extract from Vigne Vin Occitanie.