Fieragricola 2022: between Esca Diseases and Flavescenza Dorata, the health of the Italian vineyard

They are undoubtedly the most dreaded vine “diseases” because there are no effective remedies. The “esca disease complex”, which is continually and rapidly advancing, and Flavescenza Dorata, which is returning as an emergency in north-eastern Italy, are real disasters that jeopardize the life of the plants and therefore the very survival of the vineyard and its economic sustainability. The most recent research results on the “esca disease complex”, which make it possible to make prevention actions for this dreadful and unfortunately widespread disease more effective, were presented at Fieragricola (Veronafiere, March 2-5), at a conference organized by Unione Italiana Vini (Uiv) which, in 2019, launched the “Ricerca Mal dell’Esca” project, in collaboration with Laura Mugnai of the University of Florence and Stefano Di Marco of the Institute of BioEconomy (Ibe) of the CNR in Bologna, to verify the spread and severity of the disease in the main Italian wine-growing areas, thanks to monitoring of numerous vineyards and the voluntary participation of many companies.
The two researchers are the signatories of a nine-year research project - the longest ever conducted on the bait - published in the January 28, 2022 issue of Frontiers in Microbiology, a leading scientific journal in the field of microbiology. The work, illustrated by Fabio Osti of Ibe-Cner, focuses on the activity of strains of different species of a microorganism - Trichoderma - in defending against the Esca Disease Complex, opening up new perspectives. Good prospects if the cuts made on the vines during pruning, or accidentally by different phenomena such as hail, are protected immediately with sprays of the microorganism. Trichoderma colonizes the cuts and thus prevents the entry of pathogens that cause esca. The recommendation is to intervene right from the first year of planting and in good time, combining correct agronomic practices with measures to avoid spreading the pathogens (separate pruning of infected vines; disinfection of tools, removal and burning of pruning shoots, etc.). Otherwise, the spread in the vineyard is as fast as it is subtle because the symptoms appear depending on environmental conditions and not always on the same vines. This is why it is necessary to mark the symptomatic plants in order to have the pulse of the real cumulative incidence of the disease.
Fabio Osti emphasized: “the esca complex is expanding, thanks to the growing trade in plant material and the particular susceptibility of several varieties, such as Cabernet. In addition to careless pruning techniques that allow pathogens to enter the plant, extreme conditions caused by climate change are also contributing to its worsening incidence.
Applications of the Trichoderma formulation in each season showed a significant delay in the appearance of the first leaf symptoms of the disease, up to 3-4 years, compared to untreated plants. Moreover, the percentage of symptomatic plants in the treated plots was significantly lower, in most cases, than in the part of the vineyard that was not treated. Another interesting result was obtained on leaf symptom severity, showing a correlation between incidence and severity of leaf symptoms with quantitative and qualitative production losses. A reduction in the symptomatic expression of the disease on the leaf is therefore a relevant result, regardless of whether the plant is infected or not. If the rapid growth of the disease and the death of the vines were not enough, the esca complex also causes a drop in the quality of the grapes produced from the diseased plants, which adds further economic damage”. Maturation is abnormal and the composition of the musts is altered in terms of acidity and sugars, and the anthocyanin content is reduced, penalizing red grapes in particular.
“According to national monitoring, the Esca complex affects 4.8% of vines”, says Giovanni Bigot, agronomist at Perleuve, which developed the “4grapes” app used to survey diseased plants in the vineyard. “This is the average of a sample of 5,000 surveys carried out, but clearly there are some vines that are more sensitive than others. By multiplying these numbers”, Bigot explains, “we can obtain an estimate of the economic damage. The cost of uprooting a diseased vine, buying a vine shoot to replace it, replanting it, cultivation costs and the loss of production for at least three years, if all goes well, has an economic impact of 25 euros. Assuming a rate of 5% per year of symptomatic plants and a density of 4,000 vines per hectare, it is necessary to uproot and replace 200 vines per year for a loss of 5,000 euros per hectare per year. This figure must be sustained in order to maintain the profitability of the vineyard”.
The data presented by Alberto Grasso, agronomist at Azienda Agricola Mirafiore in Fontanafredda, showed that the annual man-hours needed to replace vines which have died in a Nebbiolo vineyard, and thus all the other associated costs, have risen from an average of 5 per hectare in the period 2000-2008 to as many as 34 in 2020. This reduces profits so much that the profitability of the vineyard itself is in doubt if the grapes are sold, and will be drastically reduced if the chain is closed by winemaking. In the first case, as from the 14th year of the plants' life, the income balances the costs. In addition, in the case of varieties susceptible to Flavescenza dorata, such as Barbera, the replacement of plants affected by Esca becomes economically useless, since even before the 8th year of life of the vineyard, the cultivation profit drops drastically. And we are talking about grapes and wines with designations of origin and good market value. “Unfortunately, it’s not always possible to uproot and cap all diseased plants during the season”, Bigot continues. “The grapes from these plants have different and inferior technological and phenolic maturity characteristics depending on the intensity of the symptoms. The prospects of resolving the disease are not yet there, but after 9 years of trials there are positive scientific results. We must applaud those who carried them out and invested 10 years ago in the use of micro-organisms whose effectiveness in reducing symptoms has been scientifically proven. Microorganisms are our hope for the future. Obviously, the winegrower must at the same time implement good agronomic practices, keep the vineyard in balance and increase its biodiversity”.

Even Flavescence Dorata leaves no way out: diseased plants must be eradicated as soon as possible. The survival of the vineyard itself is at risk. And what is most regrettable about this disease, caused by a phytoplasma whose vector is a cicada - the Scaphoideus titanus that also feeds on vines - is that it is an unwelcome return. A film - an ugly one - that wine-growers would never have wanted to see again and that is now affecting the North East and beyond. Photographing the situation at Fieragricola 2022 was Nicola Mori of the University of Padua in an in-depth study organized by the weekly magazine L’Informatore Agrario: “In Veneto”, explained Mori, “the areas of moderate spread are quite large and there are several where the spread is considered “epidemic”, such as the areas of the denominations straddling Verona and Vicenza, including Soave DOC, and further east Conegliano Valdobbiadene Prosecco Superiore. The increase in the incidence of the disease also concerns the province of Bolzano, which has reached 9.1% in 2021 compared to 4.1% in the previous three-year period, and that of Trento, where there are large areas declared to be “hotbeds”. In Friuli Venezia Giulia in 2019, the increase in symptoms was important especially on Chardonnay and Pinot, followed by Verduzzo friulano, Merlot, Ribolla Gialla and Cabernet, up to unexpected cases even on Tocai Friulano, a variety considered by far the least sensitive among those cultivated in Friuli Venezia Giulia. And the expansion has also heavily affected the provinces of Modena and Reggio Emilia, in particular, Lambrusco and Pignoletto”.
Gabriele Posenato, entomologist, agronomist and winegrower, who first reported the Scaphoideus titanus as the vector of Flavescenza Dorata in the 1990s, told Winenews about the causes of the resurgence of Flavescenza Dorata. “There are no longer the insecticides of the past”, jokes Posenato, who lived through the whole story of the first wave of the disease, referring to the only possible weapon, which is the fight against the vector insect. “And neither did the winegrowers of yesteryear: underestimating the symptoms”, he adds, “is unforgiving. It's a fast disease and you have to be faster than it in making decisions. As soon as you see the symptoms, you have to remove the vines and there is no other way. A combination of different factors has led to its return. The climate has changed and probably also the phytoplasma itself. The scaphoid has changed its behavior: the adult is much more long-lived and lays more eggs. It has been discovered that the adult acquires and transmits the phytoplasma within 7 to 10 days, which means that in a vineyard with many Scafoideo individuals and even a few diseased vines, in a short time, the adults can transmit the disease from infected to healthy vines to an impressive number of plants. The current recommendation is for a strict insecticide control of the vector with at least two treatments and then great attention to the uprooting of the vines. The incidence of the disease is variable. In Veneto, it is more present in the areas where it historically occurred in the first wave, such as the Treviso and Verona areas in a specific area of Soave, the Val d’Alpone, where the disease was reported in the 1990s. During these years, the Scafoideo had essentially disappeared. Insecticides have adopted “greener” molecules and defense has been oriented towards treatments against moths without any effect on leafhoppers. So the insect found a new home, re-established its populations and, finding a few “residual” infected vines in vineyards that had been run as best as possible, started to make its rounds again.