First report of <i>Grovesinia moricola</i> causing zonate leaf spot on <i>Betula nigra</i> (river birch) in Virginia

On 02 Oct 2025, at a wholesale nursery in Albemarle County, Virginia, approximately 40 out of 100 Betula nigra plants in 11.4 L containers were observed with light brown, zonate lesions and sclerotia on the leaves. Closer inspection revealed hypophyllous, pyramidal sporophores where the lesions formed, measuring 234 to 482 μm long and 75 to 111 μm wide (av. 433 x 97 μm, n = 10). Necrotic, water-soaked leaf tissue from three plants was surfaced sterilized with 70% ethanol and cultured on potato dextrose agar medium. DNA was extracted from three isolates (GS25-AE41, GS25-AE42, GS25-AE43) and the internal transcribed spacer (ITS) and 28S rRNA (28S) regions were amplified and Sanger sequenced. All three isolates had identical ITS sequences. A 510-bp fragment of the ITS region and 1,146-bp fragment of the 28S region from isolate GS25-AE41 was deposited into GenBank under accessions PX572933 and PX890849, respectively. Koch's postulates were fulfilled by placing agar plugs colonized with isolate GS25-AE41 mycelia-face down on 15 wounded Betula nigra leaves. Grovesinia moricola was reisolated from 12 out of 15 leaves while the control leaves did not form lesions. The cultures from the inoculated leaves had a 100% ITS sequence homology to isolate GS25-AE41. Grovesinia moricola has been reported from Japan on Corylus (Betulaceae), however, this is the first report of the fungus infecting a host in the genus Betula.