Diplodia bulgarica, an emerging pest of apple: addition to the EPPO Alert List
Why: Diplodia bulgarica is a pathogen causing canker on apple trees (Malus domestica) and is reported to cause significant damage in orchards. It has recently been reported in new countries in Europe and Asia for the first time. Considering the recent emergence of D. bulgarica in several EPPO countries, the EPPO Secretariat thought that it could be usefully added to the EPPO Alert List.
Where: Diplodia bulgarica was first described from Bulgaria in 2012. However, recent molecular tests of samples collected in 2009 in Iran identified D. bulgarica, which suggests that D. bulgarica may be more widespread than is currently reported. Since 2019, it has been reported in China, Poland, Türkiye and the USA.
EPPO region: Bulgaria, Germany, Poland, Serbia, Türkiye.
Asia: China (Xinjiang), India (Jammu and Kashmir), Iran.
North America: United States of America (California).
On which plants: D. bulgarica has a limited host range within the Rosaceae family. The main host is apple (Malus domestica), but it has also been reported on crab apple (M. sylvestris), wild apple (M. sieversii) and pear (Pyrus communis).
Damage: damage includes cankers, twig blight, gummosis, pre- and post-harvest fruit rot, dieback, tree decline and death. Under environmental stresses, such as drought and cold, symptom severity is greater.
Dissemination: D. bulgarica overwinters in tree cankers and conidia are released in the spring. The dissemination of D. bulgarica has not been extensively studied, but it is expected that it is similar to other Diplodia species, where the conidia can spread over short distances through water splash and wind dispersal. In international trade, the fungus may be carried by host plants for planting or on fruit or wood from infected plants.
Pathways: plants for planting, fresh fruit, wood of host plants from countries where it occurs, soil from countries where it occurs, seeds?
Possible risks: Apple and pear trees are economically important crops in the EPPO region. D. bulgarica is known to be a significant pest in Iran and Jammu and Kashmir (India). D. bulgarica has been found in a range of climates including temperate and Mediterranean/subtropical climates, suggesting it could establish in many countries in the EPPO region. More studies are needed on the biology, host range, cultivar susceptibility and geographical distribution of D. bulgarica. There is a range of control measures available, including removal of dead wood and fruit, application of broad-spectrum fungicides for apple diseases and potential biological control options using endophytic bacteria. It was previously considered that D. bulgarica was mainly present in organic production systems, however recent evidence indicates that D. bulgarica can establish and cause significant damage in conventional orchards suggesting chemical control measures may not be as effective as previously thought. Following a pest categorisation study, EFSA conclude that D. bulgarica could establish across Europe and should be considered to be a potential Union quarantine pest.
Sources
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Alijani N, Manafi Shabestari M, Ghosta Y (2016) Biocontrol effects of endophytic fungi isolated from apple trees against Diplodia bulgarica the causal agent of apple canker disease. Proceedings of 22nd Iranian Plant Protection Congress, 339.
Department of Agriculture, Food and the Marine, Ireland (2025) Express Pest Risk Analysis Diplodia bulgarica. Accessible at: https://pra.eppo.int/pra/cdbd1a84-5bb0-4e9b-ac4f-38aeac22a2fe
EFSA (2023) Pest categorisation of Diplodia bulgarica. EFSA Journal 21(6), e08070 https://doi.org/10.2903/j.efsa.2023.8070
Głos H, Michalecka M (2026) First detection of Diplodia bulgarica, a new pathogen causing black canker of apple trees in Poland. Scientific Reports 16, 7433 https://doi.org/10.1038/s41598-026-38714-1
Hagverdi S, Khakvar R, Arzanlou M, Aliasgharzad N (2024) Inhibitory effect of endophytic bacteria with auxin production ability on Diplodia bulgarica, the causative agent of apple canker in East Azerbaijan Province. Journal of Iranian Plant Protection Research 38(2), 147-157.
Hanifeh S, Zafari D, Soleimani MJ (2017) Reaction of some apple cultivars to Diplodia bulgarica in Iran. Mycosphere 8(2), 1253-1260. https://doi.org/10.5943/mycosphere/8/2/9
Julius Kuhn-Institut (2021) Express-PRA for Diplodia bulgarica. Accessible at: https://pra.eppo.int/pra/d717e30d-fcfb-49af-ac53-0ee3a5cdeafd
Nourian A, Salehi M, Safaie N, Khelghatibana F (2024) Biocontrol of Diplodia bulgarica, the causal agent of apple canker, using Trichoderma zelobreve. Archives of Microbiology 206(3), 120.
Phillips AJ, Lopes J, Abdollahzadeh J, Bobev S, Alves A (2012) Resolving the Diplodia complex on apple and other Rosaceae hosts. Persoonia-Molecular Phylogeny and Evolution of Fungi 29(1), 29-38 http://dx.doi.org/10.3767/003158512X658899