Soil management techniques for the control of juvenile populations of spittlebugs in olive groves

In the olive groves, the main factor regulating spittlebugs population level is the abundances of vegetables ground cover and its species composition. Control of the juvenile's vector population by soil tilling to reduce the emergence of adults represents one of the most efficient and environmentally sustainable approach toward the control of the spread of Xylella fastidiosa in the infected area, or to reduce the risk of its establishment in the buffer zones or free areas. In order to identify alternative strategies for soil management in olive groves, for two consecutive years (2017 - 2018) we compared five different soil management techniques: (i) natural and undisturbed ground vegetation; (ii) soil tilling performed twice (in early winter and in spring when the majority of the nymphs were at the IV instar); (iii) soil tilling performed only in winter; (iv) sowing Lolium spp; (v) sowing Hordeum vulgare. Two surveys per year were carried out. In each thesis, of approx. 3,000m2, 30 subplots of 0.25 m2 randomly distributed were surveyed by counting the number of spittle/plants and number of specimens (P. spumarius and N. campestris)/spittle. Soil tilling performed in winter and spring, effectively reduced almost to zero the presence of both spittlebug species, with an Abbott's index equal to 99.6%. Conversely, when soil tilling was performed only in winter, it proved to be effective for reducing N. campestris population (Abbott's index ranged from 50% to 60%) but not for P. spumarius. Sowing in winter Lolium spp. and Hordeum vulgare reduced P. spumarius juvenile populations, with an Abbott's index of 60% and 40%, respectively. Whereas, results were inconsistent for N. campestris: in 2017 on both Poaceae treatment, the juvenile populations were lower than on the undisturbed natural ground cover, with an Abbott index equal to 58% (Lolium) and 86% (Hordeum vulgare), while the population resulting mostly abundant during survey carried out in 2018. These data further support the effectiveness of mechanical interventions for reducing incidence of juvenile of spittlebugs, and that using poaceae species to replace the ground vegetation may contribute to lowering P. spumarius populations.