Control of olive anthracnose and leaf spot disease by bloom treatments with a pomegranate peel extract

Olive anthracnose (OA) caused by Colletotrichum spp. and olive leaf spot (OLS) caused by Ventuaria oleaginea are two of the most important diseases affecting olive trees. OA mainly affects mature olive drupes while OLS is typically known as a defoliating pathogen. Field treatments with a pomegranate peel extract (PGE) at 3, 6 or 12 g/l seven days before the expected full bloom prevented the colonization of flowers by Colletotrichum spp. and reduced latent infections in small olive drupes over the summer period by 53-100%. The same treatments significantly reduced or completely prevented the latent infections of V. oleaginea in olive leaves. Interestingly, PGE at the higher concentration (12 g/l) proved always more effective that Flint Max, a chemical formulate recently registered in Europe on olive. On plants sprayed with PGE, the lower quantity of over-summering inoculum of Colletotrichum spp. effectively delayed the disease outbreak in autumn of approximately ten days. In particular, PGE at 12 g/l reduced the incidence of anthracnose by 84.5% as compared to the untreated control. Treatments also reduced the premature defoliation of plants. Similar results to those described for a single PGE treatment made before the full bloom where achieved with two applications made before and after flowering. Overall, the present study highlighted the importance of controlling the establishment of latent infections of both Colletotrichum spp. and V.oleaginea to effectively protect olive trees. These results together with previous reports suggest the possible use of PGE as a key natural antifungal preparation to control the olive diseases affecting aerial plant organs.