Common Forest Pests and Diseases in Europe - Euc-F-1

Botryosphaeria canker and dieback

Botryosphaeria dothidea (Ascomycota, Dothideales).
synonyms : Botryosphaeria berengeriana Botryosphaeria ribis
Asexual stage: Dothoriella sp.

Host tree

Eucalyptus, Pinus, Cupressus and several fruit trees.

Identification

  • Presence of cankers on stem and branches and die-back (death of tree tops).
  • Canker evolution: first sign is the presence of a necrotic lesion in the bark (Photo 1). Usually the bark cracks around the lesion and a black reddish kino (excretion of polyphenols) exudes (Photo 2), after which the bark detaches and exposes the canker (Photo 3).
  • Symptoms can usually be seen in autumn.

Damage

  • Progressive dieback : death of tree tops due to the presence of canker(s) in the upper part of the stem and/or in the higher located branches (Photo 4).
  • Severe attacks can affect growth and may cause tree death.
  • Soft pockets of kino develop underneath the bark rendering wood unacceptable for saw timber production.
  • Lateral branches and the stem can break at the site of the cankers.

Biology

  • B. dothidea can colonise healthy trees without exhibiting virulence (latent phase) until environmental or physiological conditions favours its virulence.
  • The spores, most abundant in warm and moist conditions, penetrate the bark through small cracks and holes caused by insects or mechanical actions.
  • The combined action of biotic agents (insect pests like the Eucalyptus longhorned borer (Phoracantha semipunctata) or the Eucalyptus snout beetle (Gonipterus scutellatus) and/or abiotic factors (drought, winds, storms, unusual frost conditions, etc.) causes the weakening of the tree and favours the development of B. dothidea.

Risk factors

  • Trees in regions with incidence of P. semipunctata.
  • Trees under considerable stress (drought, winds, storms, unusual frost conditions, etc.).

Distribution

Portugal, Galice

Pest management

Preventive measurements

  • Plant eucalyptus species or clones that are well adapted to the site conditions.
  • Plant disease tolerant species or clones, when available.
  • Keep the plants growing as vigorously as possible. Avoid heavy fertilisation and severe pruning of established plants.
  • Mulch plants yearly and provide adequate water during extended dry periods (in floriculture or ornamental trees).
  • Prune out and destroy dead branches.
  • Remove and eliminate severely infected trees.

Curative control

  • Effective chemical control is not available.
Photo 1: Necrotic lesion on the bark of a Eucalyptus tree.
Photo 2: Bark cracking around the necrotic lesion and kino exude.
Photo 3: Falling of bark after cracking, showing characteristic canker.
Photo 4: Dieback of an infected Eucalyptus tree.

Illustrations : A. Vaz.


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