Diplodia blight

Written by B.E. Callan & J.P. Brandt Revision 2025

• French disease name: Brûlure des pousses terminales
• Other disease names: Diplodia tip blight, Sphaeropsis tip blight, Sphaeropsis blight
• Pathogen name: Diplodia sapinea (Fr.) Fuckel
• Kingdom: Fungi
• Phylum: Ascomycota
• Class: Dothideomycetes
• Order: Botryosphaeriales
• Family: Botryosphaeriaceae
• Partial list of synonyms:
  • Botryodiplodia pinea (Desm.) Petrak
  • Diplodia pinea (Desm.) J. Kickx f.
  • Sphaeropsis pinea (Desm.) Berk. & Broome
  • Sphaeropsis sapinea (Fr.) Dyko & B. Sutton

General information and importance

Diplodia blight (formerly Sphaeropsis tip blight) is a disease of conifers, causing significant damage to two- and three-needle pine species. In Canada, although usually present at low levels in healthy stands of native trees, the disease can cause severe damage and even lead to mortality in trees stressed by environmental factors such as drought, hail damage, or other pests. Trees of all ages are affected by shoot dieback, dead needles, blighted cones, and cankers.

Distribution and hosts

Diplodia sapinea, endemic to North America, is widespread throughout Canada where its coniferous hosts are located, particularly affecting two- and three-needle pine species that are growing outside of their natural ranges. Reports of the disease predominantly come from Ontario, although it has also been noted in British Columbia, Manitoba, Quebec, Nova Scotia, and Newfoundland and Labrador. The fungus is also found worldwide, throughout Asia, Europe, and northwestern Africa, and wherever its hosts have been introduced in South Africa, Oceania, and South America. Due to its capacity to infect its hosts and remain an asymptomatic endophyte for part of its life cycle, it is likely to have been introduced to many regions on planting stock and seeds.

In Canada, native pines affected by this pathogen primarily include lodgepole pine (Pinus contorta var. latifolia) and ponderosa pine (P. ponderosa) in western Canada, and jack pine (P. banksiana) and red pine (P. resinosa) in central and eastern Canada.

In Ontario, non-native plantings of Scots pine (P. sylvestris) and Austrian pine (P. nigra) are particularly susceptible, as well as native species that are planted beyond their natural ranges, such as lodgepole pine and ponderosa pine in Ontario. Austrian pine is the most susceptible, with Scots pine being a close second. The pathogen often affects high-value ornamental conifers and Christmas tree plantations consisting of non-native pine species.

The pathogen has also been recorded on several other species in Canada including the native balsam fir (Abies balsamea), white spruce (Picea glauca), black spruce (P. mariana), eastern white pine (Pinus strobus), tamarack (Larix laricina), and Douglas-fir (Pseudotsuga menziesii). It has been recorded on non-native species as well, such as Norway spruce (P. abies), Colorado spruce (P. pungens), Mugho pine (P. mugo), and European larch (L. decidua). More recently in Europe, the fungus has been isolated from stressed broadleaf trees in the families Betulaceae and Fagaceae.

Tree parts affected

Diplodia blight can cause shoot tip dieback, dead needles, resinous cankers on stems and branches, sapwood stain, crown dieback, and seed contamination. Pines are affected at any age from seedlings to fully mature trees.

Symptoms and signs

Trees affected by Diplodia blight show a wide variety of symptoms. The most evident symptoms include dead shoots with stunted straw-coloured needles that are adhered in place by pitch exudation located primarily in the lower third of the crown in mature trees. Trees, especially susceptible pines, often exhibit deformed crowns due to branch death from repeated, heavy infections. The dead shoots are often brittle because they are impregnated with dried resin. Infected trunk wounds may result in cankers that spread to and kill adjacent branches, creating scattered dead patches within an otherwise green crown. On tolerant trees, infections are usually limited to current-year growth and second-year cones. If the tree is stressed due to environmental factors (e.g., drought, other pathogens, or defoliating insects), infections move into the sapwood, where they cause grey to black stains.

Pycnidia are black; ovoid in shape; embedded in the host needles, twigs, or cone scales; and measure 0.2 to 0.25 millimetres in diameter. When mature, they push out to the surface and open with an apical ostiole. On needles that remain attached to branches, pycnidia can often be found underneath the fascicle sheath (papery tissue at the base of needle bundles). Conidia, produced on cylindrical cells lining the pycnidial wall, are ovoid to obovoid in shape, with a rounded apex and a slightly flattened base. Conidia are initially hyaline (colourless) or slightly yellowish, then turn dark brown, mostly 0–1-septate but up to 3-septate, measuring 10 to 16 micrometres × 30 to 45 micrometres. Conidial cell walls vary from smooth to minutely pitted.

Disease cycle

New pycnidia mature in late spring or early summer and overwinter on dead needles, infected cones (both living and dead), and the bark of living trees. They also overwinter on fallen needles, branches, and cones on the forest floor. Conidia, the primary source of infection, are exuded from pycnidial ostioles during rainy periods in the growing season. They are disseminated by rain, wind, insects, or pruning tools. Wet spring weather promotes higher levels of infection, due to the presence of susceptible soft new growth and favourable conditions for spore release. Infection occurs when conidia land on wounded tissues, new buds, young cones, elongating current-year needles, and tender shoots, especially those of seedlings. The conidia form germ tubes, which penetrate the host tissues through wounds or stomata (pores in the epidermis). Once established, infections may remain latent and asymptomatic in trees until they undergo physiological stress. Such stressors include drought, insect-feeding damage, late spring frosts, hail and snowstorm damage, suppression from competing vegetation, and poor site conditions. Foliar infections progress downwards towards the base of the needle and can proceed to infect the entire branch.

Damage

Damage to pine occurs in nurseries, afforestation and reforestation plantations, Christmas tree plantations, ornamental plantings, and natural stands. Infections may kill new shoots by the end of summer and can continue to progress into older tissues. Infected cones remaining on the tree produce inoculum, which can infect nearby branch wounds and shoots. Infected, diseased branches result in death of attached needles and cones. Infected trunk wounds, caused by physical damage such as hail, pruning, and insect feeding, can result in cambium death and canker formation. Extreme weather, such as hail and drought, can cause heavy levels of disease, both by providing new infection courts via trunk and branch wounds, and by stressing the trees so that endophytic infections become pathogenic. Severe infections or repeated infections that occur during consecutive years can eventually lead to death in trees of all ages. In the Toronto and Ottawa areas of Ontario, severe infections have caused entire trees to die within two to three years of the initial infection. Climate change and increased incidence and severity of drought is likely to exacerbate the impact of this disease in Canadian urban and natural forests. Seed can become contaminated by D. sapinea, resulting in dissemination of the disease by planting infected asymptomatic seedlings. Losses in nurseries are caused by nearby inoculum from diseased trees.

Trees planted outside their natural range are particularly susceptible due to stress from unsuitable growing conditions.

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 and population level (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 any particular pest.

Because damage due to Diplodia blight is most severe in stands of stressed trees and stressed ornamental plantings, maintaining their overall health by ensuring adequate water and soil fertility will reduce the chance of high levels of disease. It is also important to ensure that the tree species being considered for a particular site is appropriate before planting. Pruning diseased tips from high-value non-native ornamental pines can reduce spring inoculum levels, provided that pruning tools are sanitized between cuts. Thorough inspection and testing of seedlings and young trees can prevent the introduction of the disease to new areas and mitigate future disease in urban and reforested sites.

Plantations of susceptible pine Christmas trees and ornamentals can be severely damaged by this pathogen, especially for non-native species or species planted outside their natural range. In such situations and in nurseries, a fungicide may be warranted. Pesticides (including fungicides) registered for use against Diplodia blight 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 this pathogen. The application of any registered product should be based on population size and applied only when necessary and against the approved life stage. It is also recommended to consult a local tree care professional. Pesticides may be toxic to humans, animals, birds, fish, and 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

Conidia of Diplodia sapinea, the causal pathogen of Diplodia blight.

René Cauchon

Close-up view of young conidia (colourless) of Diplodia sapinea forming on cylindrical conidiogenous cells, and mature conidia (brown).

René Cauchon

Squash mount of pycnidium of Diplodia sapinea showing both conidia and conidiogenous cells.

René Cauchon

Two-celled and single-celled conidia of Diplodia sapinea.

René Cauchon

Diplodia blight causing shoot and branch mortality on Austrian pine.

Pycnidia of Diplodia sapinea. The tops of the fruiting bodies have been cut off to demonstrate the characteristic inner white colour.

Buds and needles of an Austrian pine killed by Diplodia sapinea, the causal agent of Diplodia blight.

Selected references

Blodgett, J.T.; Kruger, E.L.; Stanosz, G.R. 1997. Sphaeropsis sapinea and water stress in a red pine plantation in central Wisconsin. Phytopathology 87(4): 429–434. https://doi.org/10.1094/PHYTO.1997.87.4.429

Blumenstein, K.; Bußkamp, J.; Langer, G.J.; Terhonen, E. 2022. Diplodia tip blight pathogen’s virulence empowered through host switch. Frontiers in Fungal Biology 3: 939007. https://doi.org/10.3389/ffunb.2022.939007

Brodde, L.; Adamson, K.; Camarero, J.J.; Castaño, C.; Drenkhan, R.; Lehtijärvi, A.; Luchi, N.; Migliorini, D.; Sánchez-Miranda, Á.; Stenlid, J.; Özdağ, Ş.; Oliva, J. 2019. Diplodia tip blight on its way to the north: drivers of disease emergence in northern Europe. Frontiers in Plant Science 9: 1818. https://doi.org/10.3389/fpls.2018.01818

Bußkamp, J.; Blumenstein, K.; Terhonen, E.; Langer, G.J. 2021. Differences in the virulence of Sphaeropsis sapinea strains originating from Scots pine and non-pine hosts. Forest Pathology 51(5): e12712. https://doi.org/10.1111/efp.12712

CABI Digital Library. 2021. Sphaeropsis sapinea (Sphaeropsis blight). In Invasive species compendium. Wallingford, United Kingdom: Centre for Agricultural and Bioscience International. https://www.cabi.org/isc/datasheet/19160

Chhin, S.; O’Brien, J. 2015. Dendroclimatic analysis of red pine affected by Diplodia shoot blight in different latitudinal regions in Michigan. Canadian Journal of Forest Research 45(12): 1757–1767. https://doi.org/10.1139/cjfr-2015-0245

Denman, S.; Crous, P.W.; Taylor, J.E.; Kang, J.-C.; Pascoe, I.; Wingfield, M.J. 2000. An overview of the taxonomic history of Botryosphaeria, and a re-evaluation of its anamorphs based on morphology and ITS rDNA phylogeny. Studies in Mycology 45: 129–140.

Funk, A. 1985. Foliar fungi of western trees. Canadian Forestry Service, Pacific Forest Research Centre. Victoria, British Columbia. Information Report BC-X-265. 159 p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/f31475f4-c426-46c2-9456-21025c2c419c?fromSearchPage=true

Hausner, G.; Reid, J.; Hopkin, A.A.; Davis, C.N. 1999. Variation in culture and rDNA among isolates of Sphaeropsis sapinea from Ontario and Manitoba. Canadian Journal of Plant Pathology 21(3): 256–264. https://doi.org/10.1080/07060669909501188

Myren, D.T. 1991. Distribution of 59 organisms that cause diseases in Ontario. Forestry Canada, Ontario Region, Great Lakes Forestry Centre. Sault Ste. Marie, Ontario. Information Report O-X-410. 85 p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/0c739767-e67a-4ca1-bdac-69c2e874b89a?fromSearchPage=true

Myren, D.T.; Laflamme, G.; Singh, P.; Magasi, L.P.; Lachance, D., editors. 1994. Tree diseases of eastern Canada. Natural Resources Canada, Canadian Forest Service, Science and Sustainable Development Directorate. Canada Communication Group Publishing. Ottawa, Ontario. 159 p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/123e1f42-369f-4c95-aded-82d95f675a52?fromSearchPage=true

Nicholls, T.H.; Ostry, M.E. 1990. Sphaeropsis sapinea cankers on stressed red and jack pines in Minnesota and Wisconsin. Plant Disease 74(1): 54–56. https://www.apsnet.org/publications/plantdisease/backissues/Documents/1990Articles/PlantDisease74n01_54.PDF

Peterson, G.W. 1977. Infection, epidemiology, and control of Diplodia tip blight of Austrian, ponderosa, and Scotch pines. Phytopathology 67(4): 511–514. https://www.apsnet.org/publications/phytopathology/backissues/Documents/1977Articles/Phyto67n04_511.pdf

Scharpf, R.F. 1993. Diseases of Pacific coast conifers. United States Department of Agriculture, Forest Service. Washington, D.C. Agriculture Handbook 521. 199 p.

Sinclair, W.A.; Lyon, H.H. 2005. Diseases of trees and shrubs (2nd edition). Comstock Publishing Associates, Cornell University Press. Ithaca, New York. 660 p.

Stanosz, G.R.; Smith, D.R; Guthmiller, M.A.; Stanosz, J.C. 1997. Persistence of Sphaeropsis sapinea on or in asymptomatic shoots of red and jack pines. Mycologia 89(4): 525–530. https://doi.org/10.1080/00275514.1997.12026813

Zhang, W.; Groenewald, J.Z.; Lombard, L.; Schumacher, R.K.; Phillips, A.J.L.; Crous, P.W. 2021. Evaluating species in Botryosphaeriales. Persoonia - Molecular Phylogeny and Evolution of Fungi 46: 63–115. https://doi.org/10.3767/persoonia.2021.46.03

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