EPPO Global Database

EPPO Reporting Service no. 04 - 2002 Num. article: 2002/059

Butternut canker (Sirococcus clavigignenti-juglandacearum): Addition to the EPPO Alert List

In North America, butternut canker caused by Sirococcus clavigignenti-juglandacearum has extensively destroyed butternut (Juglans cinerea) in its native range. This fungus causes perennial cankers on branches, trunks and exposed roots. Coalescing cankers progressively girdle branches and trunks and may kill trees. S. clavigignenti-juglandacearum was first found in Wisconsin in 1967 but was probably there earlier. It now occurs in several states in north-eastern USA and in parts of Canada. Although J. cinerea is a relatively minor component of forests, it provides high quality wood and an important food source for wildlife. During the past 10 to 15 years, butternut canker has contributed to a dramatic decrease in the number of live trees (up to 80% in some states). Considering its rapid spread, its aggressive nature on J. cinerea, the scarcity of resistant trees, and its lack of genetic diversity, it is felt that this fungus has been introduced into the USA, although its origin remains unknown. S. clavigignenti-juglandacearum can be spread by rain splash, air currents and also via infected seeds. Insects may play a role in disseminating the disease, as vectors or wounding agents. In North American forests, S. clavigignenti-juglandacearum has only been reported on J. cinerea, but there are a few reports of infection of scattered trees or seedlings in nurseries on J. nigra. However, it appears in inoculation studies that J. regia and J. nigra, which are cultivated species in Europe, are susceptible to the disease. So far, no control methods are available. Research is being carried out on the use of resistant trees. Schröder et al. (2002) considered that S. clavigignenti-juglandacearum could present a serious threat to walnut production in Europe and should be added to the EU quarantine lists. In the meantime, the EPPO Secretariat decided to add it to the EPPO Alert List.

Sirococcus clavigignenti-juglandacearum (butternut canker)
Why: Sirococcus clavigignenti-juglandacearum is causing severe tree mortality on Juglans cinerea (butternut) in North America. This fungus does not occur in Europe and could present a threat to Juglans species.

Where: North America: Canada (Quebec, Ontario, New Brunswick), USA (north-eastern states).

On which plants: In North America, mortality in forests is only reported on J. cinerea. It appears that other Juglans species (e.g. J. ailantifolia var. cordiformis, J. regia and J. nigra) are susceptible to the disease. However, more data is needed on the susceptibility of these species, in particular J. regia and J. nigra which are cultivated in Europe.

Damage: S. clavigignenti-juglandacearum causes cankers on stems, branches and exposed roots. As cankers coalesce progressively, they girdle branches and stems which may led to tree death. It is estimated that S. clavigignenti-juglandacearum has contributed to a dramatic decrease of J. cinerea in USA (in some states, up to 80%). J. cinerea is not very widely present in North American forests, but it provides high quality wood and important source of food (nuts) for wildlife. Its dramatic decrease is also perceived as a threat to forest biodiversity.

Dissemination: Spores of the fungus can be dispersed by rain splash and air currents. The fungus can survive and sporulate on dead trees for at least 20 months. The fungus can also be transported on seeds of J. juncea and J. regia. Insects are most probably playing a role in disease dissemination as vectors or wounding agents, but further studies are needed. For example, conidia of the fungus were found associated with the following Coleoptera: Acoptus suturalis (Curculionidae), Astylopsis macula (Cerambycidae), Eubulus parochus (Curculionidae), Hyperplatys maculata (Cerambycidae). Feeding and egg-laying activities of Conotrachelus juglandis (Cucurlionidae) may also favour infections.

Pathway: Plants for planting, seeds, wood? of J. cinerea (J. regia, J. nigra?) from areas where S. clavigignenti-juglandacearum occur.

Possible risks: J. regia and J. nigra are cultivated in Europe and are considered as susceptible to the disease. But further data is needed, as severe infections have not been observed on these species in forests or plantations in North America. Considering the high mortality of J. cinerea and the absence of suitable control methods, S. clavigignenti-juglandacearum could present a threat to walnut cultivation in Europe.

EPPO RS 2002/059
Panel review date: -
Entry date 2002-04


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