In the complex olive grove agroecosystem, in addition to the "new" fungal diseases described in recent years (Phytophthora, Botryosphaeria and Neofusicoccum, Neofabraea, Colletotrichum spp., etc.), some mycoses generally considered pathologies of minor importance for the crop again cause considerable damage. Among these, the fungus responsible for the cercosporiosis (Pseudocercospora cladosporioides (Sacc.)—U. Braun), also known as “Plumbing” of the olive tree.
The main consequence of the disease is the premature fall of infected leaves, with general debilitation of the plant and negative effects on production and on the ability to resist biotic and abiotic attacks. Affected fruit can fall off and the oil obtained from it can have high levels of peroxides. The studies carried out have ascertained that the early phylloptosis they can determine losses of up to 20% on production of the following year. The varietal sensitivity is remarkably broad.
La disease it comes too much often confused with other pathologies of the olive tree: cycloconium, Colletotrichum, Neofabraea, etc. This, also combined with the traditional defense approach, which sees the treatments against peacock eye coincide with those for cercosporiosis, has contributed, in recent years, to the difficult management and consequent diffusion of the phytopathological problem in all the olive groves of the Peninsula.
Sulla upper face of the leaf are formed chlorotic, irregular areas, which, over time, become brownish-necrotic; in lower portion they are obvious lead-grey areas due to the presence of asexual fruiting structures of the fungus (Trapero and Blanco, 2004). The most evident symptoms are seen on the old leaves located on the branches of the lower part of the plant, even if the infections of the younger ones (4-5 months) are frequent.
La disease it is particularly severe in dense, vigorous plants and poorly ventilated. The pathogen develops more in the months with temperatures between 10° and 20°C and with high humidity (>80%), typical conditions of autumn-late winter (Avila et al., 2004). The production of conidia occurs mainly between the months of October and March. Pathogen dispersal occurs over short distances, from leaf to leaf, although it is favored by wind and rain (Junta de Andalucía, 2010). The leaves fallen to the ground seem to have a fundamental role for the survival of the fungus, being able to constitute an important source of inoculum (Trapero et al., 2009). The incubation period (time between the infection and the manifestation of symptoms) can even exceed 9 months (Trapero et al., 2011).
La defense has always been focused on copper treatments coinciding with those against peacock eye, with results not always conclusive on the disease. Studies carried out by several researchers (F. Nigro et. to the., 2000; Joaquin R. et. to the., 2020) have highlighted renewed bioecological aspects of the pathogen, with the proposal of a new temporal sequence of phytosanitary interventions. For susceptible cultivars, a succession dthe four treatments in February, April, the end of August and the end of September/October, when infections increase due to sporulation resulting from residual infections. Experiences carried out in Abruzzo in the two-year period 2019-2020 seem to confirm these data.
Between the most effective active substances, besides copper, some have been reported strobilurins, triazoles and dodine. It is interesting to mention a scientific work (Maria del Carmen Casado Muñoz et al.2017-XVIII Symposio Científico Técnico Expoliva Jaén) which tested the application of a potassium-based mineral fertilizer (18% potassium oxide) with good results.
Definitely, defense against cercosporiosis will need to be improved and focused on a correct identification of the symptoms, a sustainable agronomic management of the olive grove and on well-calibrated phytoiatric interventions in the periods of application.
FINAL NOTE – The mushroom was reported for the first time, in 1880, by Saccardo. Identified by Gonzalez Fragoso, in 1925 in Sanlùcar la Mayor, it was recognized as a pathology of the olive tree in 1941 in California and in 1952 in Italy by Pettinari, who signaled its presence in all Italian olive-growing areas and, in particular, in Puglia (Salento) (Avila and Trapero, 2010).
It presents a high pathogenetic specialization by attacking only Olea europaea L., although in North America Pseudocercopsora cladosporioides has been reported as a possible cause of leaf rot on Prunus laurocerasus (unconfirmed data).
Accademico dei Georgofili, of the National Academy of Agriculture
and of the National Academy of Olives and Oil
