First records of Microstroma album (Desmazières) Saccardo, 1878 (Basidiomycota: Microstromataceae) and Phylloxera glabra (von Heyden, 1837) (Hemiptera: Phylloxeridae) in oak stands in Bulgaria

The current study reports the first records of an aphid-like pest and leaf pathogen on oak species in Bulgaria. In 2020-2023, leaf samples presenting characteristic yellow spots and lesions were collected from mature trees of Quercus petraea, Q. cerris, Q. frainetto and Q. robur in different localities of the country. Damage caused by oak obligate leaf pathogen Microstroma album, the leaf phylloxera, Phylloxera glabra, and the oak lace bug, Corythucha arcuata were identified on the lower surface of oak leaves. M. album was identified on all studied Quercus species. Angular white patches, the fruiting stage of the fungus, appeared on the lower surfaces of the leaves. P. glabra caused yellowish mosaic discoloration on the leaf surface of Quercus cerris, Q. frainetto and Q. pertaea. Sucking damage displayed a stippled pattern of yellow, brown, or whitish dots. In places where M. album develops, the invasive oak lace bug was often found as the only sucking species on oak leaves, which is most likely also a vector of the disease. Severe damage caused by established both obligate pathogen (M. album) and sucking insect pests (P. glabra, C. arcuata) could result in a weakening of the oak trees. On sufficiently weakened trees, secondary fungal pathogens or boring insects, commonly infested oak trees, can cause their death.