Indagini sull'epidemiologia e la gestione di malattie emergenti dell'olivo

The olive tree (Olea europaea L.) is an evergreen bush native to the Mediterranean basin. In Italy, it holds immense cultural, historical, and economic significance dating back thousands of years. Recently, new diseases are causing serious damage to olive ecosystems in the Country: i) the “early drop of olives” disease, and ii) the “Olive Quick Decline Syndrome” (OQDS). The first disease is characterized by intense loss of olives in the early stage of development. No information on its aetiology was available before this PhD. OQDS is caused by the quarantine bacterium Xylella fastidiosa subsp. pauca and is mainly transmitted by the meadow spittlebug Philaenus spumarius (L.) (Hemiptera: Aphrophoridae). P. spumarius develops on ground vegetation in spring, then migrates to shrubs and trees during summer, acquiring and spreading the bacterium. On this background, this PhD thesis aimed at i) investigating aetiology and management of “early drop of drupes”, and ii) improving P. spumarius management inside and outside olive groves. In chapter 2, the role of fungi and insects in early drop of olives was assessed. Fungi did not result to be involved in olive drop either in laboratory tests or in field trials. On the contrary, the brown marmorated stink bug Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) has been shown as the major responsible for early drop of olives. In chapter 3, an insecticidal strategy to control olive early drop was investigated. Insecticide applications significantly reduced olive early drop, which resulted positively influenced by number of stink bugs present on olive trees. H. halys was the most abundant species, confirming the results reported in chapter 2. In chapter 4, the effectiveness of spring ground cover management practices in controlling P. spumarius in olive groves was evaluated. Tillage (two tillage operations in spring, followed by two cuts in summer), frequent mowing (four cuts from spring to summer) and a control (two cuts in summer) were compared. Only tillage achieved sufficient reduction of spittlebugs population, resulting a viable option for the containment of the vector in the early season. In chapter 5, the effectiveness of one insecticide application in controlling P. spumarius populations in olive groves in X. fastidiosa free areas was investigated. After a strong initial reduction of adult spittlebugs, the vector quickly recolonized the sprayed plots. In chapter 6, abundance of P. spumarius juveniles was investigated among agricultural landscapes. Vineyards showed a strong tendence to host less spittlebugs compared to other habitats. Number of spittles resulted positively affected by number of plant species and soil coverage. Considering the findings reported in this PhD thesis, H. halys proved to be a key pest of olive in northern Italy. To control this pest, it will be essential to develop more effective strategies as well as to define intervention thresholds. Regarding P. spumarius, its control will probably constitute the greatest challenge for olive protection. To limit vectors movement to olive groves, the development of push-pull strategies providing long-lasting protection and reducing insecticide applications should be considered.