Pests and pathogens threatening urban vegetation in ‘St. George’ City Park in Dobrich, northeastern Bulgaria 

Urban environments host invasive species that threaten tree and shrub vegetation in green infrastructure. In recent years, non-native pests and pathogens have been identified in Bulgaria, causing significant damage to host plants and altering the species composition of urban green spaces. The current study aimed to evaluate the risk of invasion and spread of aggressive insect pests and fungal pathogens, leading to the degradation of tree and shrub vegetation in urban green areas of a pilot site—the largest city park, ‘St. George’, in Dobrich (northeastern Bulgaria). From 2024 to 2025, the health status of 46 tree and shrub species was assessed using specific indicators, including crown defoliation, the presence of dried or rotted trees that could pose a threat to human health, and the presence of pests and pathogens that could cause allergic reactions. A mobile-based system with ArcGIS Field Maps was used to collect data during the field assessment. This system included 20 indicators for evaluating tree health status and transferring the data to electronic records. The most important pests that caused severe damage were oak ( Corythucha arcuata ) and sycamore ( C. ciliata ) lace bugs, Cinara cedri cedri , found on Cedrus atlantica ; both the leaf miner ( Cameraria ohridella ) and the horse leaf blotch fungus Phyllosticta paviae caused leaf damage and premature defoliation of horse chestnut ( Aesculus hippocastanum ) leaves. Pine species were affected by the pathogens Dothistroma septosporum , D. pini and Diplodia sapinea . The fungal pathogen Botryosphaeria dothidea caused severe blight and dieback on Sequoiadendron giganteum trees. A xylariaceous ascomycete, Biscogniauxia mediterranea , a causal agent of charcoal canker disease, was detected on Quercus cerris and Q. rubra trees. The adverse effects of invasive pests and pathogens have worsened the health of tree species and reduced the ecosystem services provided by Dobrich’s largest city park. Water stress during recent growing seasons appears to have reduced trees’ resistance and increased their vulnerability to infection by invasive pests and pathogens.