Nectria canker
- French disease name: Chancre nectrien
- Other disease names: Apple canker, European canker, target canker
- Pathogen name: Neonectria ditissima (Tul. & C. Tul.) Samuels & Rossman
- Kingdom: Fungi
- Phylum: Ascomycota
- Class: Sordariomycetes
- Order: Hypocreales
- Family: Nectriaceae
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Partial list of synonyms:
- Cylindrocarpon heteronema (Berk. & Broome) Wollenweb
- Dialonectria galligena (Bres.) Petch
- Nectria ditissima Tul & C. Tul
- Nectria galligena Bres.
- Neonectria galligena (Bres.) Rossman & Samuels
General information and importance
Nectria canker is a common fungal disease in eastern hardwood forests and occurs on a variety of host species. It is also an important disease in apple orchards and occurs on susceptible ornamental tree species.
In forests, most losses are to young trees because cankers typically affect most of the circumference of infected main stems. Although older trees can be infected as well, cankers are usually restricted to branches, which may be killed depending on the size of the canker. The impact on the overall crown is minimal. During windstorms, stem breakage can occur at older, larger cankers.
The fungal pathogens, Neonectria ditissima and N. faginata, in combination with two scale insects, Cryptococcus fagisuga (beech scale) and Xylococculus betulae (birch margarodid), are responsible for beech bark disease (dealt with separately within the database). Beech scale was first detected in Halifax on European beech (Fagus sylvatica) about 1890. Beech bark disease was first reported in Nova Scotia in 1930. The latter disease has been spreading throughout the range of American beech (F. grandifolia) due to the spread of beech scale, which is a non-native species from the Black Sea region of Europe.
Distribution and hosts
Nectria canker is common in eastern Canadian temperate hardwood forests. It is rare in western Canada. The fungus responsible for Nectria canker attacks a wide variety of temperate broad-leaved trees, such as maple (Acer), alder (Alnus), birch (Betula), hawthorns (Crataegus), beech (Fagus), ash (Fraxinus), walnut (Juglans), ironwood (Ostrya), poplar (Populus), oak (Quercus), willow (Salix), basswood (Tilia), and elm (Ulmus). It also attacks fruit trees (apples [Malus] and pears [Pyrus]) and several shrubs, such as currant (Ribes) and holly (Ilex).
Research indicates that, in general, Nectria canker is more severe in wetter temperate climates. This may explain the low incidence of this disease in the drier Prairie Provinces.
The disease can be found in many parts of the world where temperature and moisture conditions are suitable.
Tree parts affected
Symptoms and signs
The first symptom of fungal attack is small, dark sunken areas on the bark of young trees, often associated with bud or leaf scars, twig or branch stubs, or previous wounds. These small cankers are not easy to detect without careful examination of the host.
Once established in the host, the fungus is perennial.
Older cankers lack bark, and the exposed wood forms ridges of concentric callus tissue, often resembling a “target.” A branch stub or knot is often visible in the middle of these “target” cankers.
The sexual state of the fungus produces small (<0.5 millimetres diameter), orangey red to dark red ovoid perithecia (fruiting bodies), which usually occur in groups of up to 30 on the dead bark at the canker’s edge. Perithecia produce microscopic ascospores. Ascospores are ellipsoid to fusiform, with narrowly rounded ends, hyaline (transparent or colourless), 1-septate, often slightly constricted at the septum, smooth to very finely spinulose (small spines), and about 16.9 micrometres × 7.4 micrometres in size.
The asexual state produces sporodochia, which are small, white, cushion-shaped fruiting bodies that produce conidia (spores). The microscopic conidia are cylindrical, with rounded ends, straight to slightly curved, 5-6 septate, and about 75.9 micrometres × 7.1 micrometres in size. The red perithecia are typically more visible than the white sporodochia.
There are two other species of Neonectria commonly encountered in Canada. These species are:
- the native N. faginata on beech in eastern North America (also linked to beech bark disease); and
- the introduced N. coccinea, (also on beech in eastern Canada and the United States but native to Europe).
The closely related native fungus, Nectria cinnabarina, is more commonly associated with crown dieback in several hardwood species and has a global distribution.
Disease cycle
The fungus overwinters as perithecia or mycelium in cankers on stems, twigs, or branches. Two types of fruiting bodies are produced by Neonectria, which under favourable weather conditions can occur simultaneously. The two types are:
- asexual, which appear in the form of white sporodochia located in crevices of recently killed bark of young cankers; and
- sexual, which appear in the form of clusters of orangey red to dark red ovoid perithecia that develop in the second year after canker formation and in older infections.
The perithecia form on the bark adjacent to the canker during or soon after wet weather. The ascospores they produce play a more important role in disease spread than conidia. Ascospores are spread during wet weather by rain splash and wind. These dispersed ascospores begin new infections at bud or leaf scars, twig or branch stubs, and other tree wounds. New infections often occur on younger trees. Ascospores germinate, and the fungus colonizes the bark and surface of the wood.
Nectria cankers develop slowly, especially during periods when the host is growing in the spring and summer. Once tree growth slows in late summer and fall, or under stress conditions, the fungus advances into healthy tissue through the release of toxins that kill the host tissue before colonization. In the spring, when tree growth resumes, the host develops callous tissue to try to seal the wound, only to be killed again later in the season. The cycle is repeated each year, resulting in the appearance of successive ridges of callous tissue in the general shape of a target.
Nectria cankers achieve the highest spore production at temperatures of 10 to 16°C. Optimal spore germination occurs between 20 to 25°C, with a lower limit of 1°C and an upper limit of 30°C. Wetness is critical to infection. Minimum surface wetness for leaf scar infections is 24 hours at 10°C, 10 hours at 15°C, and as little as 2 hours at 20°C.
Damage
Trees weakened or stressed by other factors such as frost, drought, wounds, or pests are susceptible to Nectria canker.
Trees with older cankers that affect most of the stem’s circumference are vulnerable to wind damage.
Decay is rarely a problem within cankers, except for birch and alder.
This pathogen is considered the most damaging stem disease of birch. It is also a destructive disease in apple production, where control is often warranted to avoid serious economic consequences.
As mentioned earlier, the fungal pathogens, Neonectria ditissima and Neonectria faginata, and two scale insects, Cryptococcus fagisuga (beech scale) and Xylococculus betulae, interact together to cause beech bark disease. The latter disease is one of the more significant forest diseases in eastern North America in terms of temporal and spatial extent, as well as the negative impact on its host, American beech.
Prevention and management
Pest management strategies for a particular pest vary depending on several factors. These include:
- the population level of the pest (i.e., how numerous the pest is on the affected host[s]);
- the expected damage or other negative consequences of the pest’s activity (either to the host, property, or the environment);
- an understanding of the pest’s life cycle, its various life stages, and the various natural or abiotic agents that affect population levels;
- how many individual host specimens are affected (an individual tree, small groups of trees, plantations, forests);
- the value of the host(s) versus the costs of pest management approaches; and
- consideration of the various silvicultural, mechanical, chemical, biological, and natural control approaches available and their various advantages and disadvantages.
Decisions about pest management strategies require information about each of these factors for informed decision-making. These various factors should then be weighed carefully in terms of costs and benefits before action is taken against a particular pest.
Nectria canker cannot be controlled in forests. Maintaining healthy, vigorous trees, however, minimizes losses. Thinning overly dense stands or completing improvement cuts to maintain stands at optimal density, with special attention to removing cankered trees during these cuts, is beneficial.
Maintaining tree health and vigour is also important for ornamental trees. Keeping trees well-watered and occasionally fertilized is helpful. Trees should not be pruned during wet periods or in the spring (when the weather is usually wetter). Pruning tools should be sanitized before pruning the next infected host tree. Protecting trees from mechanical injury to avoid potential points of disease infection is also a good practice.
In apple orchards, careful monitoring and stringent pruning when the weather is dry (to minimize new infections) can control the amount of available inoculum. Applying a protective fungicide after pruning can reduce exposure to infection.
Pesticides registered for use against Neonectria ditissima under specific situations may change from year to year. Therefore, please search Health Canada’s Pesticide Product Information Database for currently registered pesticides and product information for use against the pathogen. The application of any registered product should be based on population size and applied only when necessary and against the approved disease stage. It is also recommended to consult a local tree care professional. Pesticides may be toxic to humans, animals, birds, fish, and other beneficial insects. Apply registered products only as necessary and follow all directions and precautions noted on the manufacturer’s label. In some jurisdictions and situations, only a licensed professional can apply pesticides. Consulting relevant local authorities to determine local regulations that are in place is recommended.
Photos
Norway maple branch killed by a canker caused by the fungus Neonectria ditissima.
André Carpentier
Canker caused by Neonectria ditissima on the trunk of sugar maple.
André Carpentier
Callus swelling at the margin of a canker caused by Neonectria ditissima on sugar maple.
André Carpentier
Perithecia (fruiting bodies, sexual state) of Neonectria ditissima, the pathogen responsible for Nectria canker, on the margin of a canker on sugar maple.
Denis Lachance
Canker caused by Neonectria ditissima on the trunk of white birch.
Perithecia (fruiting bodies, sexual state) of Neonectria ditissima, the pathogen responsible for Nectria canker, on the margin of a canker on white birch.
Selected references
Agriculture and Agri-food Canada. 2019. Crop profile for apple in Canada, 2016. Fourth edition. Pest Management Program. Agriculture and Agri-Food Canada. Ottawa, Ontario. 94 p. https://publications.gc.ca/site/eng/9.867685/publication.html [Accessed April 2024]
Beresford, R.M.; Kim, K.S. 2011. Identification of regional climatic conditions favorable for development of European canker of apple. Phytopathology 101(1): 135–146. https://doi.org/10.1094/PHYTO-05-10-0137
Bussières, G.; Innes, L.; Laflamme, G.; Tremblay, J. 2009. Maladies des arbres du Québec. Centre collégial de développement de matériel didactique. http://arbres.ccdmd.qc.ca [Accessed April 2024]
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(9): 1417–1433. https://doi.org/10.1139/b06-105
Cale, J.A.; Garrison-Johnston, M.T.; Teale, S.A.; Castello, J.D. 2017. Beech bark disease in North America: over a century of research revisited. Forest Ecology and Management 394: 86–103. https://doi.org/10.1016/j.foreco.2017.03.031
Ghasemkhani, M. 2012. Genetic basis for resistance against fruit tree canker in apple. Swedish University of Agricultural Sciences, Balsgård. Introductory paper at the Faculty of Landscape Planning, Horticulture and Agricultural Science. 2012: 7. 40 p.
Latorre, B.A.; Rioja, M.E.; Lillo, C.; Muñoz, M. 2002. The effect of temperature and wetness duration on infection and a warning system for European canker (Nectria galligena) of apple in Chile. Crop Protection 21(4): 285–291. https://doi.org/10.1016/S0261-2194(01)00099-0
Lortie, M. 1981. Nectria canker of hardwoods. Environment Canada. Canadian Forestry Service. Laurentian Forest Research Centre. Sainte-Foy, Quebec. Information Leaflet CRFL 10E.
Lortie, M.; Kuntz, J.E. 1963. Ascospore discharge and conidium release by Nectria galligena Bres. under field and laboratory conditions. Canadian Journal of Botany 41(8): 1203–1210. https://doi.org/10.1139/b63-101
Plante, F.; Hamelin, R.C.; Bernier, L. 2002. A comparative study of genetic diversity of populations of Nectria galligena and N. coccinea var. faginata in North America. Mycological Research 106(2): 183–193. https://doi.org/10.1017/S0953756201005329
Sinclair, W.A.; Lyon, H.H. 2005. Diseases of trees and shrubs. Second edition. Comstock Publishing Associates, Cornell University Press. Ithaca, New York. 660 p.
Weber, R.W.S. 2014. Biology and control of the apple canker fungus Neonectria ditissima (syn. N. galligena) from a northwestern European perspective. Erwerbs-Obstbau 56: 95–107. https://doi.org/10.1007/s10341-014-0210-x
Zalasky, H. 1968. Penetration and initial establishment of Nectria galligena in aspen and peachleaf willow. Canadian Journal of Botany 46(1): 57–60. https://doi.org/10.1139/b68-011