Phytophthora abietivora: an emerging pest of fir trees in North America
Phytophthora abietivora is a recently reported Phytophthora species that was first reported to cause root rot and death of Abies fraseri trees in Connecticut (USA) in 2019 (EPPO RS 2020/137). Since 2019, further reports of P. abietivora have been made from nurseries, plantations and native forests across North America.
- In a study conducted between 2019 and 2021, P. abietivora was identified as the causal agent of shoot dieback, needle reddening, resinosis and discolouration (known as Phytophthora root rot) of Fraser fir (Abies fraseri) and balsam fir (A. balsamea) seedlings in Christmas tree plantations in Chaudiere-Appalaches and Estrie, Québec, Canada (Charron et al., 2024).
- In a survey to identify Phytophthora spp. across Pennsylvania (US), sampling was conducted on forest plants, soils and waterways between 2018 to 2020. P. abietivora was the most frequently isolated Phytophthora species from mature plants, saplings and seedlings of 10 native broadleaf plants including Acer rubrum, Betula lenta, Carya sp., Cornus florida, Fagus grandifolia, Hamamelis virginiana, Ilex montana, Quercus alba, Q. montana and Q. rubra. The most common symptoms included stem canker, foliar necrosis, shepherd’s crook and shoot blight (Bily et al., 2022).
- In October 2025, P. abietivora was identified as a causal agent of chlorosis, root necrosis and death of balsam fir, A. balsamea, seedlings in a forest nursery of St-Modeste, Québec, Canada. Due to the severity of the outbreak, the Canadian Food Inspection Agency recommended the destruction of the entire A. balsamea production in spring 2023 (Charron et al., 2025).
Recent evidence suggests that P. abietivora has been present in the Eastern USA since at least 1989, but was likely misidentified as P. europaea based on morphological and phylogenetic similarities. A study that re-examined preserved plant pathogens from Pennsylvania found that P. abietivora occurred in 1989, 1993, 2002 and 2009 on infected roots of Abies fraseri and Tsuga canadensis (Molnar et al., 2020).
Sources
Bily D, Nikolaeva E, Olson T, Kang S (2022) Phytophthora spp. associated with Appalachian oak forests and waterways in Pennsylvania, with P. abietivora as a pathogen of five native woody plant species. Plant Disease 106(4), 1143-1156 https://doi.org/10.1094/PDIS-05-21-0976-RE
Charron G, Gauthier MK, Aucoin V, Tanguay P (2025) Outbreak of Phytophthora abietivora in a Québec forest nursery: emergence of a new phytophthora tree pathogen? Forest Pathology 55(5), e70041 https://doi.org/10.1111/efp.70041
Charron G, Yergeau J, Van der Heyden H, Bilodeau GJ, Beaulieu C, Tanguay P (2024) Survey of Phytophthora diversity reveals P. abietivora as a potential Phytophthora root rot pathogen in Québec Christmas tree plantations. Plant Disease 108(6), 1445-1454 https://doi.org/10.1094/PDIS-12-23-2670-SR
Molnar C, Nikolaeva E, Kim S, Olson T, Bily D, Kim JE, Kang S (2020) Phytophthora diversity in Pennsylvania nurseries and greenhouses inferred from clinical samples collected over four decades. Microorganisms 8(7), 1056 https://doi.org/10.3390/microorganisms8071056