20051012 Evergreen Tree Canker Diseases

Evergreen Tree Canker Diseases

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A large number of cankers occur on evergreens that cause dieback. These are more common on stressed trees planted in marginal sites or infect poorly maintained trees. Young cankers are slightly darker in color than adjacent bark and appear slightly sunken.

As cankers enlarge they kill the living woody tissue within the trunk or branch. Canker growth may cause the bark along the edges to crack and fall away, exposing the dead wood underneath. After a canker enlarges enough to girdle a branch or trunk, the portion beyond the canker dies. Small twigs are killed more quickly than larger branches. Symptoms may include progressive upper branch dieback, disfigured branch growth, or target shaped areas on trunks with concentric rings of dead bark.

Seiridium Canker

Seiridium canker is a fungal disease that can attack cypress and junipers. The most common landscape plant in Maryland that is infected is Leyland cypress.

This disease is caused by the fungus Seiridium cardinale. The first symptoms usually appear in the spring or early summer, as a fading or yellowing of the foliage on branches, or the tops of trees. These symptoms gradually lead to browning of affected parts. The fungus causes girdling lesions around the bases of branches or main stems, and these lesions characteristically exude large amounts of resin. Trees may be killed if many small cankers occur or if large enough to girdle the main stem. The reproductive spore forming structures (acervuli) appear as small black dots embedded in the bark near the canker margins. During wet weather the infective spores are dispersed by rain, but they can also be spread by wind, insects and pruning tools.

Management: There are no chemical controls for this disease. The best strategies for disease prevention are avoiding stresses to the plants. Provide adequate water during dry periods, avoid over crowding of trees, and don't over mulch or plant too deeply.

Cytospora canker

A common canker disease of both blue and Norway spruce trees is Cytospora canker. Typical symptoms include poor growth, profuse sap flow and pitch accumulation (white resin patches) on lower branches, and eventual dieback of lower branches. Diagnostic symptoms are revealed after cutting into pitch coated bark and finding dark resin soaked wood along with small black dots just under the bark. These small black dots, are the spore producing structures. In wet weather, the infectious spores ooze out as small yellowish threads, that can be spread by rain to other branches in the tree.

Management strategies: There are no chemical controls for cankers and they cannot be stopped once they become extensive. Pruning off affected branches back to healthy wood is the only control measure available. Drought stressed trees should be watered during dry weather to promote better tree vigor.

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