This study was conducted in the Plant Protection Department /College of Agriculture/ Basra University for the season 2019-2020. This study aimed to study leaf spot disease in oleander plant. The results of the field survey showed the presence of leaf spot disease in all regions, It showed the results of isolating the fungi C. hawaiiensis and C. sphaerospermum from the leaves of the oleander plant, the results of the pathological ability test indicated that these two fungi were capable of causing leaf spot disease, the results of the pesticide test showed the growth of fungi C. hawaiiensis and C. sphaerospermum, Where it was found that the most effective pesticides in inhibiting C. hawaiiensis It is fungicide Topas Where the inhibition rate reached 82.15% at a concentration of 300 ppm, and the least fungicide is the fungicide Aliette Express That amounted to 11.17% in concentration With a concentration of 300 ppm either C.sphaerospermum, The more pesticides Inhibition is fungicide Topas That amounted to 85.29% with a concentration of 200 and 300 ppm and the lowest pesticides that inhibit the fungus C. sphaerospermum It is Proxanel 37.05% at a concentration of 100ppm The study showed that all the used fungicides affected the sporulation of the isolated fungi, and that the most effective pesticides on the fungus spores C.sphaerospermum It is fungicide and Ortiva and Difecor As the number of spores in it reached zero. The results of the contrast test indicated the presence of high antagonism among the fungi Trichoderma koningi, and pathogenic fungi Curvularia hawaiiensis and Cladosporium sphaerospermum, where was the T.koningii inhibiting the growth of pathogenic fungi, as it reached the degree of antagonism (1) with both fungi, The results showed that the biological fungus had a positive role in increasing the peroxidase enzyme, as it gave the highest treatment of the biological fungus Tricho +Curvu+ Clado. Which amounted to 0.0976 units / g-wet weight compared to the comparison treatment, as the average peroxidase enzyme was 0.0128 units / g-wet weight. The results of the Symbiotic effect of the pesticide and the biological fungus on the severity of infection with the fungi that because the oleander spotted disease showed that the treatment with the pesticide, as well as the biological fungus, reduced the severity of the disease.