Olive (Olea europaea L.) in Croatia is being cultivated since ancient times. Today along the Adriatic coast we can find olive trees that are hundred years old, which show the millennial tradition of Croatian olive growing. Olive is attacked by diseases and pests, and the most significant disease is peacock eye leaf spot. Peacock eye leaf spot appears on sensitive varieties, and on varieties with thick dregs in which humidity is maintained what is suitable for the development of pathogenic fungi. The aim of this research is to detect the plague-bearing infection in the olive grove in Crno. Olive orchard consists of 30 trees. The infection is estimated before and after treatment on the edges and in the interior of the crown. The infection is revealed with two methods, the first method is visual, and the second method is of concealed infection. The visual is done by visual evaluation of the infection and second method by using a 5% NaOH solution. From the results of the research in the visual method it is seen that the infection is greater in the interior of the crown, which is 81% before treatment, and 38% after the treatment. On the edges, the pre-treatment was 70% and after treatment 21%. In the method of concealed infection in the interior of the canopy the infection was 90% before treatment and 75% after treatment. At the edges of the canopy of infection, it was 91% prior to treatment and 43% after treatment. The study concluded that infection in the interior of the canopy is greater than on the edges because the inside of the crown is tight and moisture is maintained, and that the copper agent helps to suppress the peacock eye leaf spot, but the interior of the skull is dense, high and therefore difficult to reach.