Neonectria canker of Abies spp. in Denmark and Norway: a new emerging disease
Since 2008, a new and severe canker disease has been observed on firs (Abies spp.) in Norway. In 2011, the same disease was also found in Denmark. A Neonectria species was consistently isolated from samples collected from diseased fir trees in Denmark and Norway. Symptoms are characterized by dead shoots and branches, cankers, and heavy resin flow. Tree mortality has often been observed on Abies spp. in landscape plantings, Christmas tree production fields, and forest stands. In Denmark, the Neonectria species was also found on trees and seeds in a seed orchard of A. nordmanniana, thus suggesting that the disease might be seed-transmitted. Under humid conditions, characteristic red perithecia with ascospores (perfect stage) occasionally develop on plant material that has been dead for some time (usually more than 1 year). In both Norway and Denmark, this new Neonectria canker disease has been observed on Abies grandis (grand fir), A. procera (noble fir), A.;nordmanniana (Nordmann fir), A. amabilis (Pacific silver fir), A. pinsapo (Spanish fir), A.;sibirica (Siberian fir), A. lasiocarpa (subalpine fir), and A. concolor (white fir). In particular, heavy attacks have been recorded on A. nordmanniana in Denmark, and on A.;lasiocarpa in Norway. The disease was also observed on Picea abies (Norway spruce) in the vicinity of dying A. concolor.
During studies carried out to identify the species of Neonectria involved in this new canker disease, molecular analysis showed that all isolates of this Neonectria sp. were most similar to N. ditissima (commonly attacking apple and other broadleaved trees) and clearly distinct from N. fuckeliana (attacking conifers). Isolates from Norway and Denmark were morphologically and genetically identical. Inoculation tests to A. lasiocarpa resulted in needle cast and dead shoots within less than a month, indicating that the pathogen was very aggressive. The fungus could be re-isolated from the inoculated shoots. It is currently considered that the species which is damaging Abies spp. in Denmark and Norway is Neonectria neomacrospora (anamorph Cylindrocarpon cylindroides). The biology and epidemiology of this fungus remain largely unknown. Concerning its geographical distribution, N. neomacrospora is reported to occur in North America, and there are some old records of its presence in Europe (outside Denmark and Norway) but not in association with severe tree canker outbreaks. It is assumed that the disease is spread by aerial spores. The possible interactions between N. neomacrospora and insects (e.g. Dreyfusia nordmannianae (Hemiptera: Adelgidae) or Cryphalus piceae (Coleoptera: Scolytidae)) need to be clarified. As this new canker disease is particularly severe in Christmas tree plantations, control measures are being recommended to growers (destruction of diseased trees, and fungicide treatments).
Sources
Poster by Talgø V, Thomsen IM, Nielsen UB, Brurberg MB, Stensvand A (2011) Neonectria canker on subalpine fir (Abies lasiocarpa) in Denmark. Bioforsk (NO). http://www.bioforsk.no/ikbViewer/Content/100752/Neonectria_VT_v1.1_A3.pdf
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.
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). http://bfw.ac.at/400/pdf/fsaktuell_54_8.pdf
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). http://www.skovdyrkerne.dk/uploads/media/Neonectria_2.pdf
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.
Thomsen IM, Strømeng GM, Talgø V (2013) [Neonectria canker I. Biology and epidemiology]. Københavns Universitet. Skov ; Landskab. Videnblade Pyntegrønt 5.6-25 (in Danish). http://www.skovdyrkerne.dk/uploads/media/Neonectria_1.pdf
Thomsen IM, Talgø V (2013) [Neonectria canker III. Symptoms and control]. Københavns Universitet. Skov ; Landskab. Videnblade Pyntegrønt 5.6-27 (in Danish). http://www.skovdyrkerne.dk/uploads/media/Neonectria_3.pdf