Neonectria canker of Abies

Introduction

Neonectria canker of Abies is an emerging disease caused by the fungus Neonectria neomacrospora (also previously known as Cylindrocarpon cylindroides). It causes severe cankers on fir trees (Abies spp) leading to crown dieback. Although this disease was first described from grafted white fir (Abies concolor ) in a German nursery more than 100 years ago and has been known Europe for decades, it was only in 2008 when the high damage levels were first reported in Norway and in Denmark in 2011.

There have also been sporadic reports of this disease in Britain in the 1960s and the 1990s. However, we have seen a re-emergence of the disease on different Abies spp in 2015 when several cases were reported to the Tree Health Diagnostic and Advisory Service (THDAS) of Forest Research.

Geographical distribution and susceptible species

Neonectria neomacrospora is reported to occur in North America, and there are old records of its presence in Europe (outside Denmark and Norway) although not causing severe tree canker symptoms.

In Europe the disease has been reported from at least 13 species of Abies and these are listed in Table 1. In particular, heavy attacks have been recorded on Nordmann fir in Denmark and on subalpine fir in Norway. The disease has also been observed infrequently on Norway spruce (Picea abies) in the vicinity of dying white fir and on western hemlock ( Tsuga heterophylla).

Since 2015, the disease has been confirmed on a largely similar range of fir species in England and Wales, with affected species also detailed in Table 1.

Table 1. Abies species associated with Neonectria neomacrospora in mainland Europe and the UK

Abies species

Common name

Affected in Europe

Affected in the UK

Abies alba

European silver fir

Abies amabilis

Pacific silver fir

Abies balsamea

Balsam fir

 

Abies cephalonica

Greek fir

Abies concolor

White fir

 

Abies durangensis

Durango fir

 

Abies fargesii

Farges fir

 

Abies fraseri

Fraser fir

 

Abies grandis

Grand fir

Abies kawakamii

Taiwan fir

 

Abies koreana

Korean fir

 

Abies lasiocarpa

Subapline fir

Abies magnifica

Red fir

 

Abies nebrodensis

Sicilian fir

 

Abies procera

Noble fir

Abies nordmanniana

Nordmann fir

 

Abies pinsapo

Spanish fir

Abies sibirica

Siberian fir

Abies vejarii

Vejar fir

 

       

How it spreads

The biology and epidemiology of this fungus are largely unknown. It is assumed that the disease is spread by aerialy and the conidia (asexual spores) of the fungus are dispersed locally by rain splash and it is possible that strong winds may disperse them over longer distances. Transmission via contaminated or infected seed has also been reported although the frequency with which this occurs is unknown.

Insects such as the small fir bark beetle (Cryphalus piceae) may also play a role as vectors, especially as this particular species of bark beetle has become prominent in Denmark at around the same time as the disease started to emerge. However, although Neonectria disease and C. piceae are often found together on affected trees, there is no confirmed link so it may be that the beetle is simply able to take advantage of disease-stressed trees. The needle and shoot sucking aphid ( Adelges sub gen. dreyfusi) does appear to have a role in increased levels of fungal attack based on a statistical correlation between the amount of damage and the occurrence of this adelgid. In Britain, cultures of N. neomacrospora have been isolated from the distorted twig growth caused by adelgid feeding but the disease can also occur in the absence of adelgid damage.

Spread has probably also occurred through the movement of infected trees into previously unaffected areas.

Symptoms

Dead tips and dieback caused by Neonectria neomacrospora on noble fir (Abies procera)Initially dead tips (Fig 1) or

 

 

 

Figure 2. Dieback on lower branches of Fraser fir (A. fraseri) as a result of Neonectria neomacrospora infection.dead shoots are observed in the lower branches (Fig. 2)

 

 

 

Figure 3. Dying branches of (a) European silver fir (A. alba) and (b) Taiwan fir (A. kawakamii)although they can also be seen all over the affected tree (Fig 3).

 

 

 

 

Figure 4. Cankers caused by Neonectria neomacrospora on noble fir (A. procera)Affected branches or trunks show cankers (Fig. 4), and resin flow that can be abundant. When the canker girdles the branches or the trunk, the part of the tree above the canker dies back.

 

 

 

 

 

Figure 5. Characteristic red fruiting bodies (perithecia) on affectd branches of noble fir (A. procera)In late autumn and winter and under humid conditions, characteristic small, rounded, red fruiting bodies called perithecia (Fig. 5) which contain the spores of the fungus, can develop on the affected parts or on plant material that has been dead for some time (usually more than 1 year).

 

 

 

 

Figure 6. Close up of the red fruiting bodies of Neonectria neomacrospora in clusters on noble fir (A. procera)The red fruiting bodies resemble insect eggs as they usually found in clusters (Fig. 6).

 

 

 

 

 

 

Figure 7. Dead Taiwan firs (A. kawakamii) as a result of Neonectria neomacrospora infectionBadly affected tree with extensive dieback will die (Fig. 7).

 

 

 

 

 

Impact

Tree mortality has often been observed on Abies spp. in landscape plantings, Christmas tree production fields, and in forest stands. In Denmark, Neonectria has also been found in on trees and seeds in a seed orchard of A. nordmanniana, consistent with other findings of seed-transmission.

Treatment

No effective control measures against N. neomacrospora in forest stands have been reported to date, and information about possible control methods in nurseries or in parks and gardens is scarce with methods mainly limited to sanitation and improved hygiene. Where practical, affected branches or shoot tips should be removed, cutting back to the healthy wood. Stringent biosecurity measures should also be taken to clean tools and reduce the possibility of spread from tree to tree as well as between sites. Consideration should be given to the risk posed by introducing new plants to sites where the disease is not present. As this new canker disease is particularly severe in Christmas tree plantations in some countries, control measures are being recommended to Christmas tree growers which include destruction of diseased trees and fungicide treatments.

Status

Neonectria neomacrospora is not currently listed as a quarantine organism in the European Union’s Plant Health Directive. It is recognised as a potential risk by the Defra Plant Health Risk Group and added to the Risk Register .However, the lack of information and taxonomic confusion on whether this was a new species delayed the drafting of a PRA.

To report sightings

Ana Perez-Sierra (England/Wales)

Steven Hendry (Scotland)

Further information

Brurberg M. B., Stensvand A. & Talgø, V. (2015). Development and application of a PCR-based test for the identification of Neonectria neomacrospora damaging Abies species. 12th International Christmas Tree and Extension Conference, page 34.

Castlebury L.A., Rossman A.Y. & Hyten A.S. (2006) Phylogenetic relationships of Neonectria / Cylindrocarpon on Fagus in North America. Canadian Journal of Botany, 84, pp1417-1433.

GBIF (Global Biodiversity Information facility) (2013) 

Ouellette G.B., Bard G. (1966) A perennial canker of balsam fir on Anticosti Island. Plant Disease Reports 50: 722–724.

Peace, TR. (1962). Pathology of trees and Shrubs with Special Reference to Great Britain. Oxford at the Clarendon Press, Oxford.

Strouts RG, Rose DR, Brown SE. (1991). Advisory services - Wales and southern England. Report on Forest Research 1991. p 34. HMSO: London.

Talgø V, Brurberg MB, Stensvand A (2009) Neonectria canker on true fir and spruce in Norway. Proceedings of the 9th International Christmas Tree Research and Extension Conference (Corvallis ; Puyallup, US, 2009-09-13/18), 58-62.

Talgø V, Thomsen IM, Nielsen UB, Brurberg MB, Stensvand A (2011) Neonectria canker on subalpine fir (Abies lasiocarpa) in Denmark. Proceedings of the 10th International Christmas Tree Research and Extension Conference (Eichgraben, AT, 2011-08-21/27), 92-96.

Talgo V, Thomsen I-M, Ravn HP. (2013). Neonectria aedelgrankraeft II. Vaertplanter og samspil med insekter. 5.6.26.

Talgo V., Thomsen I.M. & Stensvand A. (2009) A Neonectria canker has become a serious problem on true fir in Norway and Denmark. IUFRO Work Unit, Volume 5 (1).

Talgo V, Riley K, Coats K & Chastagner G.A. (2014) Neonectria canker on true fir in western USA. Poster

Talgø V, Thomsen IM, Stensvand A (2013) A Neonectria canker has become a serious problem on true fir in Norway and Denmark. IUFRO Work Unit 2.02.09 Christmas Tree Newsletter 5(1), 7-9.

Online resources

https://gd.eppo.int/reporting/article-2696

Poster by Talgø V, Thomsen IM, Nielsen UB, Brurberg MB, Stensvand A (2011) Neonectria canker on subalpine fir (Abies lasiocarpa) in Denmark. Bioforsk (NO). 

Talgø V, Thomsen IM, Nielsen UB, Brurberg MB, Stensvand A, Cech T (2011) New species of Neonectria as a cause of cankers on true firs (Abies spp.) in Scandinavia. Forstschutz Aktuell 54, 33-37 (in German). 

Talgø V, Thomsen IM, Ravn HP (2013) Neonectria canker II. Host plants and interaction with insects]. Københavns Universitet. Skov ; Landskab. Videnblade Pyntegrønt 5.6-26 (in Danish). 

Thomsen IM, Strømeng GM, Talgø V (2013) Neonectria canker I. Biology and epidemiology. Københavns Universitet. Skov ; Landskab. Videnblade Pyntegrønt 5.6-25 (in Danish). 

Thomsen IM, Talgø V (2013) Neonectria canker III. Symptoms and control. Københavns Universitet. Skov ; Landskab. Videnblade Pyntegrønt 5.6-27 (in Danish).

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