DROSOPHILA SUZUKII IN THE VINEYARDS: SPECIAL MONITORING

The new parasite that sparked alarm amongst vine-growers has shown not to be harmful to grapes but will be constantly monitored with food traps to avoid unexpected developments.


The tiny moth that arrived in Italy in 2009 creating much worry amongst the vine-growers in many regions, is not a threat to the vine but should be keep under control with special surveillance. This was the message that emerged from the seminar organised by Fieragricola in collaboration with the Consorzio per la Tutela dei Vini Valpolicella focusing on the danger of these moths.
“We wanted to give clarity on the Suzukii month”, said Olga Bussinello, director of the Consorzio, “we invested in the monitoring and observation of this new parasite which, in our case, could have been particularly important during the appassimento phase in the fruit drying lofts. Here, in fact, the completion of process with the insect present can create considerable economic damage in light of the high price of the grapes used for producing Amarone”.
The programme, carried out by the Consorzio per la Tutela dei Vini Valpolicella over the past three years, aims to promote the importance of work in the vineyard and control the steps in the production process of the Valpolicella appellation wines. The monitoring and research on D. suzukii, is part of this mission as the moth presented a potential danger to the grapes and production of wine.
“The Asian moth should be feared for a number of reasons,” explained Alberto Grassi from the Fondazione Mach at San Michele all’Adige (Trento), “such as the ability of the female to pierce the skin and deposit eggs inside the grapes creating micro fissures, the short life cycle, the high number of generations with the rapid increase in the population. If these were not enough, D. suzukii is very good at adapting and creates problems exactly in the period of the harvest when defending against such pests is difficult”.
“From the first years of this experimental monitoring of the presence in the vineyard”, assures Luisa Mattedi of the Fondazione E. Mach of San Michele all’Adige (Trento), “we can confirm that D. suzukii is not aggressive on the grape. However, this does not mean we can let our guard down. We must constantly keep it under control for our peace of mind. The other important aspect,” added Mattedi, “is that attacks during the harvest, do not create particular problems, except for cases where grapes are also suffering from hail damage. Only in this case can we find the decay that has been found in other types of fruit following an attack.”
In the case of cherries and small fruits penetrated by D.suzukii, defence treatments are inevitable however for vines, these are used in only extreme circumstances. “In Trentino”, explained Mattedi, “we are trying treatments with bentonite, kaolin, and potassium silicate that create an impenetrable film over the grapes”. The Asian moth was first detected in Alto Adige in 2011 in such quantities to merit specific treatments.
“In 2012 and 2013”, said Florian Sinn of the Beratungsring Südtirol, “the damage was contained. The sensitivity of the variety Schiava should be noted yet the eggs are inhibited from developing. We found that microclimatic conditions created in the pergola are more favourable to D. suzukii compared to those in the espalier system. For this reason we think that good management of the foliage, meaning pruning, can also be considered a preventative measure.”
In the area of Verona, the research was carried out in several vine-growing valleys where the vineyards are planted close to cherry trees as well as in the fruit-drying lofts where the grapes are left to dry before they are used to make Amarone della Valpolicella and Recioto della Valpolicella.
“The samples showed the presence of the insect”, said Renzo Caobelli, consulting agronomist for the Consorzio per la Tutela dei Vini Valpolicella. “However, just before the harvest, with a moderate number of adults of both sexes, there was no sign of egg deposits on the grapes. The experiments carried out on the traps demonstrated that the deciding factor is the presence of food bait and not the colour or the shape of the trap. It is irrelevant that the trap is too red as the D. suzukii moth is indifferent to this colour. Regarding the sensitivity of grape varieties, which was of particular interest to us, we don’t have conclusive evidence given the results of the attacks found.”
“Only in the vineyards located on the high hilly areas,” underlined Enrico Marchesini of Agrea research centre, “the density of the population was clearly higher than that registered in the mid to low hilly and valley floor areas. This allowed us to deduce a certain varietal preference of D. suzukii: for red, medium to late maturing grapes, the indigenous varieties Corvina and Rondinella are more susceptible than international varieties such as Merlot and Cabernet Sauvignon. There is a close relationship between the attack of eggs in the vineyards and a consequent presence of D.suzukii in the fruit drying loft,” continued Marchesini. “The temperature of the drying areas influences the number of adults captured and the duration of their development. Furthermore, the females are capable of depositing their eggs also on the grapes that are left to dry.”
Looking at the experience with D.suzukii in Switzerland and Europe, other areas have confirmed the findings of the Italian tests. “D. suzukii prefers red grapes with thin skins, such as Bondoletta and Gamay in Switzerland,” said Mauro Jermini of Agroscope Changins-Wädenswil ACW Research Centre Cadenazzo in Switzerland. After this come Pinot Noir and red Divico with slightly thicker skins and then the white grapes Müller-Thurgau and Chasselas. It is also interesting that none of the eggs deposited at the beginning of the ripening of the grapes then developed into adults, therefore the rate of transformation into moth remained very low. Furthermore, observations on the field and preliminary laboratory tests indicated that the infestation on the grape bunch does not favour either the development of other moths, nor rot inside the grapes.”
In summary, in the areas of Switzerland that found deposits on the grapes, D. suzukii larvae did not develop therefore they did not contribute to the increase in population of the insect. This comforting finding was also the conclusion of a study carried out by Agroscope on 14 wine producing regions (equal to approx. 10% of Europe’s vineyards). The management of the insect should concentrate on prevention and D. suzukii is currently considered in Europe as a minor grape parasite.