Survey on Ulmus spp. Health in Latvia and Records of Ophiostoma novo‐ulmi

Elms, a vital component for biodiversity and ecosystem services, are declining due to the Dutch elm disease (DED) caused by Ophiostoma novo‐ulmi . This study investigated the occurrence of visible DED symptoms, the health condition of elm trees, and the distribution of O. novo‐ulmi subspecies in 58 young elm‐dominated stands across Latvia, surveyed in 2016/2017 and 2023. The proportion of stands with symptomatic elms was higher in stands surveyed in 2023 than in 2016/2017 (82% and 61%, respectively); however, the proportion of symptomatic trees within the stands remained constant. Among the two native elm species in Latvia, Ulmus laevis showed less frequent symptoms than Ulmus glabra (99% and 89% showed no visible signs of disease, respectively). Due to the low occurrence of symptomatic trees, the effects of stand‐level properties on the infection risk could not be reliably estimated. In 2017 and 2023, O. novo‐ulmi was confirmed via laboratory methods in 65% and 37% of the samples, representing 69% and 50% of the sampled stands, respectively. Based on morphological and molecular identification, among 31 isolates in 2017 and 23 isolates in 2023, 28 and 22 were O. novo‐ulmi subsp. novo‐ulmi , respectively. Three isolates in 2017 and one isolate in 2023 were identified as the hybrids of subsp. novo‐ulmi and subsp. americana . Based on the overall health condition of the trees, some resistance of local elm populations and their ability to regenerate might be cautiously suggested.