Elytroderma disease

Written by B.E. Callan Revision 2024

• French disease name: Rouge élytrodermien
• Other disease names: Elytroderma needle cast
• Pathogen name: Elytroderma deformans (Weir) Darker
• Kingdom: Fungi
• Phylum: Ascomycota
• Class: Leotiomycetes
• Order: Rhytismatales
• Family: Rhytismataceae

General information and importance

Elytroderma disease causes needle cast and brooms (large, bushy branch proliferations) on ponderosa (Pinus ponderosa) and lodgepole pines (P. contorta var. latifolia) in western Canada. It differs from other pine needle cast fungi by also penetrating branch tissue where it causes systemic infections across many years. Damage is most severe on ponderosa pine, and on this host, it is the most important foliar disease in the Pacific Northwest. Jack pine (P. banksiana) is also susceptible to Elytroderma disease, but on this host, it only causes needle cast.

Distribution and hosts

Elytroderma deformans is endemic to North America. It occurs from British Columbia eastward to Ontario, including Yukon and the Northwest Territories, and has been reported in New Brunswick on jack pine. Elsewhere in North America, it can be found in the western United States, including Alaska, where its pine hosts occur.

Elytroderma disease affects only two- and three-needle pines. Seven species of pine are known hosts in North America. In Canada, ponderosa pine is most severely affected throughout its range, especially in areas with moist environmental conditions, such as river drainages. Lodgepole pine is also susceptible, as is jack pine and shore pine (P. contorta var. contorta), but the pathogen only causes needle cast on the latter two hosts.

Host parts affected

The entire crown of the tree is affected. Needles are cast prematurely, and trunks and branches become deformed from systemic infections causing witches’ brooms.

Symptoms and signs

Trees with heavy systemic Elytroderma disease develop conspicuous dense patches of branches known as “brooms” or “witches’ brooms”. In ponderosa pine, the branches in the brooms are very short, causing the long needles to overlap in tufts. Tips of systemically infected branches become flagged with reddened foliage. Bark of infected branches develop elongated resinous lesions. Prior to hysterothecium formation, subepidermal blisters up to 1 millimetre long and filled with conidia develop on the needles. The blisters are the same colour as the needles, and ooze tendrils of hyaline (colourless) slender conidia measuring 6 to 8 micrometres × 1 micrometre. Hysterothecia appear as narrow black lines on the outer surface of the needles, varying in length, up to 10 millimetres long, and opening by a centre split along the long axis during wet weather to expose the light brown hymenium. The hymenial layer consists of tightly packed asci interspersed with sterile hyphae called paraphyses. Asci are sac- to club-shaped, 8-spored, measuring 140 to 240 micrometres × 30 to 45 micrometres. Ascospores are hyaline, cylindrical, 1-septate, measuring 90 to 120 micrometres × 6 to 9 micrometres, and coated in a thick gelatinous sheath.

Lodgepole pine dwarf mistletoe, a parasitic plant, also causes witches’ brooms on lodgepole pine and jack pine, but the presence of the small dwarf mistletoe plants on swollen branches are diagnostic features that readily identify this pathogen.

Disease cycle

Elytroderma deformans overwinters as hysterothecia on dead needles both on the ground and still attached to the tree, as well as in recently infected asymptomatic needles and colonized branch tissues. Branch tissues remain infected for many years and the fungus can grow from it into needles, resulting in new foliar infections. The pathogen is also disseminated by ascospores that are ejected from the hysterothecia on infected needles and spread by wind and rain in late summer and fall. Some ascospores may also be ejected in the following spring. Under conditions of high humidity (rain or dew) and cool temperatures, ascospores germinate, and the fungus grows through the needle tissues and penetrates to the twig tissues before the needle dies. Needles die in the spring following infection, turning reddish-brown. Dying needles first develop tiny inconspicuous blisters filled with conidia. The function of the conidia in the disease cycle is unknown, for example their role as infective propagules and/or spermatia. Hysterothecia are produced in the summer, after which the needles are shed from the tree during fall rains. Once established in woody tissues, the fungus growth progresses outward with the host shoot growth and also grows back towards the trunk, thus infecting other branches and ultimately the trunk.

Damage

Damage is caused by branch and stem deformation, and growth reduction from defoliation and reduced cambial growth in systemic infections. The impact is highest on young trees or trees with poor crowns. Infected trees are predisposed to root disease or bark beetle attack. In central British Columbia, some mature pine plantations have up to 30% of trees with systemic crown infections and witches’ brooms.

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.

Some heavily infected pine plantations in British Columbia are managed in the following manner: infected trees are considered acceptable for retention if at least 50% of the crown is healthy, and the upper crown is still growing. If the leader has been killed and the top of the canopy is rounded, the infection is considered too great for acceptance as a well-spaced crop tree. In some circumstances, premature harvest to salvage timber in severely damaged plantations is warranted.

Selected references

Allen, E.A; Morrison, D.J.; Wallis, G.W. 1996. Common tree diseases of British Columbia. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria, British Columbia. 178 p.

Childs, T.W. 1968. Elytroderma disease of ponderosa pine in the Pacific Northwest. United States Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. Portland, Oregon. Research Paper PNW-69. 46 p. https://www.biodiversitylibrary.org/item/171912#page/3/mode/1up [Accessed August 2024]

Childs, T.W.; Shea, K.R.; Stewart, J.L. 1971. Elytroderma disease of ponderosa pine. United States Department of Agriculture, Forest Service, Forest Pest Leaflet No. 42. 6 p. https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fsbdev2_043238.pdf [Accessed August 2024]

Funk, A. 1985. Foliar fungi of western trees. Canadian Forestry Service, Pacific Forest Research Centre. Victoria, British Columbia. BC-X-265. 159 p.

Hunt, R.S. 1978. Elytroderma disease of pines. Forestry Canada, Forest Insect and Disease Survey, Forest Pest Leaflet No. 27. 4 p.

Roth, L.F. 1959. Perennial infection of ponderosa pine by Elytroderma deformans. Forest Science 5(2): 182–191. https://academic.oup.com/forestscience/article-pdf/5/2/182/23085878/forestscience0182.pdf

Rusch, D. 2020. Elytroderma needle cast on lodgepole pine in British Columbia. Province of British Columbia. Victoria, British Columbia. Land Management Handbook 74. 5 p.

Scharpf, R.F. 1990. Life cycle and epidemiology of Elytroderma deformans on pines in California. Pages 7–12 in W. Merrill and M.E. Ostry, editors. Recent research on foliage diseases: Conference Proceedings, Carlisle, Pennsylvania, 29 May – 2 June 1989. United States Department of Agriculture, Forest Service. Washington, D.C. General Technical Report WO-56. 145 p.

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.

Cite this fact sheet

Photos

Broom symptoms of Elytroderma disease caused by the fungus Elytroderma deformans.

Bob Erickson

Discoloured needles resulting from infection by Elytroderma deformans.

Eric Allen

Discoloured needles resulting from infection by Elytroderma deformans.

Eric Allen

Broom symptoms typical of Elytroderma disease.

Eric Allen

Slit-like fruiting bodies of the fungus Elytroderma deformans.

John Hopkins