Poland's urban tree populations are exposed to a range of fungal, bacterial, and insect-related health threats. Several diseases that have spread significantly across Central Europe over the past two decades are now established in Polish forests and city parks. Early recognition and containment remain the most effective approaches available to tree owners and municipal arborists.
Ash dieback (Hymenoscyphus fraxineus)
Ash dieback, caused by the fungus Hymenoscyphus fraxineus (previously known as Chalara fraxinea), arrived in Poland from the east in the 1990s and has since affected ash populations throughout the country. The pathogen spreads via spores released from infected leaf debris on the ground.
Symptoms to look for
- Wilting and browning of shoots and leaves in mid-summer, starting at the crown tips
- Diamond-shaped or elongated lesions (cankers) on young shoots and stems, often with a darker margin
- Epicormic shoots emerging from the trunk below the dying crown
- White or grey fungal fruiting bodies on fallen leaf stalks in late summer
No chemical treatment is effective against ash dieback in field conditions. Management focuses on removing dead and dying material to reduce spore load, and on monitoring for resistant individuals — some ash trees show tolerance and may be candidates for conservation.
Chestnut blight (Cryphonectria parasitica)
The fungal pathogen Cryphonectria parasitica has devastated sweet chestnut (Castanea sativa) populations across southern and western Europe. In Poland, sweet chestnut is not as widely distributed as in France or Italy, but the disease has been recorded in Lower Silesia and Małopolska where chestnut grows in parks and botanical collections.
The pathogen enters through wounds and bark cracks, forming sunken, reddish-orange cankers that girdle branches or the main trunk. Infected tissue above the canker dies as the fungus blocks water and nutrient transport in the vascular system.
Containment measures
- Prune infected branches at least 30 cm below the visible canker margin
- Disinfect tools with 70% alcohol or dilute bleach before moving to another tree
- Do not compost infected wood; chip and dispose off-site, or burn where local regulations permit
- Biological control using hypovirulent strains of the pathogen has been trialled in Italy and France — consult GDOŚ (General Directorate for Environmental Protection) for current guidance in Poland
Dutch elm disease (Ophiostoma ulmi / O. novo-ulmi)
Elm (Ulmus spp.) was once a dominant component of Polish lowland floodplain forests and urban avenues. Two successive waves of Dutch elm disease, caused by Ophiostoma ulmi and the more aggressive O. novo-ulmi, eliminated the majority of mature elms in Poland through the 20th century.
The fungus is transmitted by elm bark beetles, primarily Scolytus species. Beetles breed under bark of dying or recently felled elm and carry spores to feeding sites on healthy trees, introducing the pathogen into the vascular system. Yellowing and wilting of individual branches in spring or early summer — known as "flagging" — is the typical first visible sign.
Current status in Poland
Surviving elms are predominantly suckers from root systems of dead trees, or hedgerow specimens that escaped beetle colonisation. Some municipal arborists in Warsaw and Wrocław have been trialling disease-resistant elm cultivars developed in the Netherlands and the United States, including 'Lutèce' and 'Columella'.
Bacterial bleeding canker (Pseudomonas syringae pv. aesculi)
Horse chestnut trees in Polish parks and streets have shown increasing symptoms of bleeding canker caused by Pseudomonas syringae pathovar aesculi. Dark, bleeding lesions appear on the bark — often around the base and lower trunk — and may extend to girdle the tree over several years.
The disease is exacerbated by waterlogged soils and root zone compaction. Improving drainage around affected trees and avoiding mechanical damage to the trunk during maintenance may slow progression. There is no curative treatment; affected trees should be monitored for structural safety risk.
General prevention principles
- Avoid creating unnecessary wounds through mowing, strimming, or vehicle contact — entry points for pathogens
- Do not move wood or soil from areas with known disease outbreaks to clean sites
- Diversify species composition in urban plantings: monocultures amplify disease impact
- Report unusual symptoms on trees in public spaces to the local gmina or the relevant Regional Inspectorate for Environmental Protection (RDOŚ)