Abstract <p>The results of the four-year monitoring (2022–2025) of the emerald ash borer (EAB) <i>Agrilus planipennis</i> Fairmaire in the Rostov Region are presented. During this period, the pest widely spread across the region, infesting ash stands in 18 (primarily in the western part) of the region’s 43 administrative districts (i.e., 40% of the region’s area). As a result, quarantine phytosanitary zones were established in the region over a total area of 3.186 million hectares. By the end of 2025, more than 90% of ash trees of three species (<i>Fraxinus pennsylvanica</i>, <i>F. excelsior</i>, and <i>F. ornus</i>) were damaged significantly in shelterbelts, roadside forest belts, recreational areas, and street plantings; 30 to 60% of the trees were dying, and about 20% were already dead. The infestation of ash trees varied: 0.1 to 1.9 exit holes per 1 dm² of bark surface were recorded on ashes in shelterbelts and from 0.1 to 1.6 per dm² in urban landscapes. A study of 68 model trees in the Neklinovskiy district and in the city of Rostov-on-Don demonstrated no significant differences in the density of exit holes across trunk height from 0 to 2 m. Three cases of tree roots infestation by EAB were documented in park stands in Rostov-on-Don. In the stands under study, mature trees of <i>F. pennsylvanica</i> exhibited more intense bark cracking than <i>F. excelsior</i>—in 90% of cases, the bark appeared trimmed, with significant light-colored areas visible from a distance. In the forest belts of the region, a mass infestation of young shoots with a diameter of 3.18–7.6 cm and epicormic branch with a diameter of 1.75 cm has been detected. A negative forecast has been given for the plantings of <i>Fraxinus</i> spp. in the Rostov Region.</p>