Combined progress in symptoms caused by Hymenoscyphus fraxineus and Armillaria species, and corresponding mortality in young and old ash trees

•Old trees show signs of serious weakening and increased mortality.•Severely damaged trees grew 80% less in diameter compared to healthy trees.•Severe stem necrosis observed later than severe crown damage on unhealthy trees.•A. cepistipes was associated with ash dieback for the first time in Denmark.