Elm tree

Ulmus spp.

1. Identification and origin

Elms (Ulmus spp.) are deciduous trees of the Ulmaceae family, distributed across Europe, Asia and North America. In Portugal, the most notable are Ulmus minor Mill. (European elm), Ulmus glabra Huds. (wych elm) and Ulmus laevis Pall. (white elm). Traditionally used in urban plantings, agroforestry systems and as shade trees, they have suffered a marked decline due to Dutch elm disease or graphiosis of elms.

2. Economic importance

Historically, elms had great importance in urban afforestation, timber production and traditional agricultural systems. At present, the economic value is limited owing to the high mortality caused by Dutch elm disease. They persist, however, as species relevant to genetic conservation, biodiversity and ecological recovery.

3. Botanical characterisation

Elms are trees of medium to large size, reaching 20–35 m in height. The leaves are simple, alternate, ovate, with a serrate margin and an asymmetric base. The flowers are small, apetalous, appearing before the foliage. The fruits are winged samaras, dispersed by the wind. The root system is deep and vigorous, conferring good mechanical resistance.

4. Soil and climate requirements

Elms adapt to temperate climates, tolerating winter cold and moderate summers. They prefer deep, cool and well-drained soils, with a pH between 6.0 and 7.5. They are sensitive to prolonged droughts and to waterlogging. They develop well on river banks, valleys and fertile soils.

5. Main pests

• Bark beetles (Scolytus scolytus, Scolytus multistriatus) — borings in the wood and vectors of Dutch elm disease
• Aphids (Tetraneura ulmi) — leaf galls and reduction of vigour
• Caterpillars (Operophtera brumata, Colotois pennaria) — loss of leaf area
• Weevils (Rhynchaenus ulmi) — galleries in young leaves
• Soil nematodes (Pratylenchus spp.) — reduction of root vigour

6. Main diseases

• Dutch elm disease (Ophiostoma ulmi, Ophiostoma novo‑ulmi) — lethal vascular wilt, transmitted by Scolytus spp. beetles
• Trunk cankers (Nectria spp.) — bark lesions and decline
• Powdery mildew (Erysiphe ulmi) — white coating and reduction of photosynthesis
• Leaf spots (Phloeospora ulmi) — necroses and premature leaf fall
• Root rots (Armillaria spp.) — progressive decline and death of the tree

7. General crop management

The management of elms centres on the prevention of Dutch elm disease, including removal of infected wood, monitoring of Scolytus spp. beetles and use of tolerant cultivars. Pruning should be carried out outside the flight period of the vectors. Maintaining cool and well-drained soils favours the vitality of the trees. In urban afforestation, diversification of species is recommended to reduce phytosanitary risks.

Bibliographic references

• EPPO Global Database – Ulmus spp.
• CABI – Crop Protection Compendium – Ulmus spp.
• Brasier, C. M. (2000). The rise of the hybrid Ophiostoma novo‑ulmi. Plant Pathology, 49, 1–11.
• Solla, A. et al. (2005). Influence of plant age on susceptibility of Ulmus minor to Dutch elm disease. Forest Pathology, 35, 421–430.
• Richens, R. H. (1983). Elm. Cambridge University Press.