CUTTING OFF TRUNKS OF BOIS NOIR-AFFECTED GRAPEVINES: A CULTURAL PRACTICE TO ENHANCE THE DISEASE RECOVERY PHENOMENON

 (pubblicato su 1st European Bois noir Workshop 2008)

R. Credi(1), F. Terlizzi(1), N. Reggiani(2), M. Bacchiavini(3)

(1) Dipartimento di Scienze e Tecnologie Agroambientali, Alma Mater Studiorum - Università di Bologna, Viale Fanin 40, 40127 Bologna, Italy
(2) Consorzio Fitosanitario Provinciale di Modena, Via Andreoli 13, 41100 Modena, Italy
(3) Consorzio Fitosanitario Provinciale di Reggio Emilia, Via F. Gualerzi 32, 42100 Reggio Emilia, Italy


Introduction
Bois noir (BN) occurs, often with high incidence and economic losses, in all Italian viticultural areas. Vitis vinifera cultivars may display symptoms of variable severity; persistent disease expression year after year has been observed, but symptom remission can also occur.
Management of BN is a very difficult task. Among the possible defence lines, it is likely that certain cultural practices could help in limiting disease incidence. So, a study was setup to evaluate the effect of two pruning methods on a large population of affected vines. The current results are reported here and their significance briefly discussed.

Materials and Methods
Trials were established in the Modena and Reggio Emilia provinces of
Northern Italy. Eight commercial vineyards, with a 6.1% mean incidence of BN, were chosen: four of the cv. Ancellotta planted in 1997-1999 and four of the cv. Lambrusco Salamino planted in 1997-2001. All grapevines were cordon trained and Sylvoz-pruned. The therapeutic efficacy of
cutting off vine trunks at 50 cm above ground (lower pollarding) and cutting off vine cordons only (upper pollarding) was evaluated. During the winter of 2003, 230 and 237 diseased grapevines
were treated using the two methods, respectively; these plants were subsequently managed to reconstitute the original training system. As a control, 340 diseased grapevines Sylvoz-pruned as usual were instead chosen. Observations for BN expression were then made during the 2004-2006 summers. The trials were conducted according to a complete randomized design using the individual vines as the experimental unit. Data were analyzed with SAS system software using the Log-Linear Model technique (CATMOD procedure); chi-square test (at P ¡Ü 0.05) was used to compare means.

Results and Discussion
The efficacy of cutting permanent organs in grapevines affected by BN, during the winter after the observation of foliar symptoms, was examined over a period of three years. High rates of recovered vines were registered among the Ancellotta and Lambrusco Salamino populations that served as our experimental controls: in average 64.6% and 64.3%, respectively. The lower pollarding or upper pollarding managements, however, significantly improved the phenomenon of disease symptom remission. As compared with the nontreated grapevines, in treated Ancellotta grapevines the mean incidence of recovery was 80.8% (P = 0.01) and 68.5%, respectively. In Lambrusco Salamino, these techniques were even more effective: 84.8% (P = 0.05) and 77.8% (P = 0.05) of grapevines showed remission of BN expression, respectively (see Figure).
Based on the results presented in this report, it can be concluded that an heavy winter pruning of mature BN-diseased grapevines, such as cutting off their trunks or cordons, may be a cultural practice to take into consideration in the control strategy frame for this important grapevine yellows.