• Invasive – nematodes of this genus are found in the Pacific Rim (Korea, Japan and New Zealand).
  • The disease causes leaf deformity in beech trees of all ages.
  • Young trees die as a direct result of this disease.
  • First detected in Ontario in 2017, the disease is present along the shore of Lake Erie and in Toronto.

“Invasive” refers to a species that has moved outside of its native habitat and threatens the new environment, economy or society by disrupting local ecosystems.

Host species

Beech leaf disease is found in:

  • forests with American beech (Fagus grandifolia)
  • plantings of European (sylvatica), Oriental (Fagus orientalis) and Chinese (Fagus engleriana) beech in North America

Characteristics and life cycle

  • Nematodes are present in leaves before symptoms occur.
  • Nematodes feed on leaf tissue between veins, causing leaf damage.
  • Nematode numbers increase from spring to fall and they overwinter in buds and leaf litter.
  • How the nematode is spread is unknown and research is underway; other nematodes are spread by mites, insects, animals and in infected plant material.

Symptoms and damage

  • Early symptoms are dark-green stripes or bands between lateral veins of leaves.
  • Severe symptoms include thickened or leathery leaves that may be yellow, curled or deformed; leaves may drop early and buds may not develop.
  • Sapling-sized trees may die within two to five years, with older trees taking longer to show effects.
  • Infected trees can be more susceptible to other pathogens.

Beech leaves showing the characteristic dark green stripes  between some of leaf veins

Control measures

The nematode thought to cause beech leaf disease can unintentionally be spread to non-infested forested areas.

To stop the spread, do not move:

  • beech seedlings
  • leaf litter
  • firewood