The prevention of Esca disease

Apertura-portaleOver the past years, Italian vineyards have been exhibiting symptoms of Esca complex wood disease, which have reached, in some cases, quite worrisome levels. Unfortunately this trend is not taking a turn for the better.
And to think that back in 1986 Esca was a disease only known to phytopathologists or the most expert of technical specialists. Then it was associated with wood decline since it was only found in the oldest of vines and was relatively rare.

From 1986 on

Two terrible frosts occurred in Italy, one in 1979 and again in 1985. The first devastating frost, with lows down to -28/-29°C in the Po Valley and other areas, was deadly for many vineyards which had to be completely re-constructed afterwards. The second, with milder temperatures (down to just -20/-23°C), did not kill the vines except for a few cases. Therefore it was sufficient to retrain the plants with heavy pruning and only in replant some of the vines.
Everything seemed to be resolved but that wasn’t really the case. No one took into consideration that the surviving plants had been injured. On the part of the trunks closest to the soil there were micro-wounds which subsequently acted as a pathway for the onslaught of various pathogens, giving rise to infections that started becoming evident the following year (an important point is the latency period of these infections). This took place particularly in the plants that today we call non-hardy varieties, in which symptoms of Esca disease started to be noticed on a wide basis. In the following years, the situation worsened.
Today we know that it’s fundamental and strategic to eliminate infected vines as soon as possible from the vineyard since they serve as a source of inoculum. The fungi that make up the Esca disease complex have a long latency period. They infect the plant by developing internally and only when there are concomitant triggering factors will the classic symptoms of the disease appear.

Origin and spread

Esca disease, or the Esca complex, based on current understanding, is due to tracheomicotic and cariogenic fungi that are found both singly and jointly.
The tracheomicotic fungi settle in the vascular tissues and give rise to black gum, spots and streaks. The cariogenic fungi attack the lignin and the cellulose, causing the wood to weaken and, in the final stages, it crumbles into sawdust.
In the past this disease manifested itself mainly in adult plants but currently it has been also found in young plants. Depending on the age of the stricken plant, brown streaking can already be noted on rooted vines, rootstocks and scions. This streaking shows up in the vascular apparatus when the propagation material is investigated, since the plant itself often doesn’t show any symptoms. In the case of young vines with slow growth, withered and chlorotic leaves, we find Petri disease, a variant of Esca. On production vines, we find the so-called young Esca (striped leaf disease) without cankers. Finally in the more advanced stage we have Esca proper with cankers which are typical of old vineyards.
The spread of the fungal agents is currently believed to be mainly linked to the dissemination of spores both in the winter as well as during the vegetative phase. In both periods, infections are aided along by the presence of wounds. According to the results of a recent study, the spread of the infection from one plant to another via pruning tools is now thought to be less significant.

Prevention today

Over the past decades results from curative treatments have proven to be negligible. More important is prevention or the elimination of infected material and parts suspected to be infected as rapidly as possible after the symptoms appear. As soon as symptoms are determined to be from Esca, not just the cordons, but the entire plant must be removed. The longer this is put off, the greater the possibility that removal will be ineffective.
Given this scenario, the curative treatments adopted in the past (utilizing various fungicides and fungistatic agents) have not been convincing. Cures have been attempted with oil emulsions or Sodium Arsenite in France or the more recent Triazoles and Fosetyl-Al. The variables linked to success are innumerable and probably not yet clear, therefore not subject to consideration.
The most current approach in the last several years has been to fight Esca naturally with biological enemies.

Biological fight: test still in progress

Since 2010, Isagro, in cooperation with local producers, has been conducting numerous tests on different varieties in North Central Italian vineyards. They have been utilizing a biological fungicide based on two strains of Trichoderma asperellum and Trichoderma gamsii.
The tests (conducted with the same protocol) have taken place over 5 years and data have been collected over a sampling area of at least 500 plants in order to evaluate the evolution of the disease over the years. This long-term testing approach has been necessary since the symptoms of the disease are not always visible every year.
The impact of the tested product is exclusively preventive and therefore the application is carried out between mid-March and the beginning of April. The insulation of the pruning wounds by the Trichoderma colonies has confirmed the capability of the vines to stabilize and survive the entire growing season, creating a barrier that fights the fungal pathogens.
Before the harvest, the state of health of each of the treated vines is recorded, with a specific code for any possible symptoms displayed. In addition, any retraining and removed dead plants are recorded. The applications and sampling are repeated for a period of at least five years.

Highlight: THE SYMPTOMS

Grapevines can display two types of Esca forms, acute or chronic, in unpredictable periods and ways. The acute form is apoplexy where the plant, in a day’s time, passes from full and healthy growth (totally or just parts of the vine) to being completely withered or dry. This often occurs with first high summer temperatures. The chronic form presents tiger striped leaves with tissues between the veins passing from chlorosis to completely drying out and grapes that then shrivel up. This symptom first strikes new leaves and in many cases progresses throughout the season, until the entire plant dries out and results in partial or total production loss. These symptoms, that often do not result in the immediate death of the vine, lead to believe that the vine can recover and be cured. However experience has proven that sooner or later the Esca symptoms will re-appear and the vine is destined to die.

Highlight: A COMPLEX FRAMEWORK

It has been scientifically proven that Esca is caused by the production of mycotoxins by fungi that are responsible for the disease, concomitant with other abiotic factors such as the physiological state of the vine, weather, water conditions (excess or lack of water), nutritional imbalances (for example C/N ratio) and last but not least, agronomic anomalies.

Highlight: AUTHORITIES INVOLVED

Experimentation with the biological fungicide based on Trichoderma asperellum and Trichoderma gamsii started in 2010 and has taken place over five years, coordinated by Isagro S.p.A. with help from the University of Firenze and CNR-Ibimet of Bologna as well as with the participation of the Plant Health Consortium of the Region of Emilia Romagna.

Article by Anselmo Montermini, Director of Plant Health Consortium of Reggio Emilia and Modena – Italy

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