Several conifer samples have been submitted to the ISU Plant Disease Clinic with the symptoms of canker diseases. The written description usually mentions individual, scattered branches suddenly dying and resin oozing from the branches or trunk.
However, the sample usually doesn't contain the canker (a diseased area that is usually sunken and discolored). Browning branch tips are often submitted, when the cankered area is actually closer to the trunk or even the main trunk. It can sometimes be difficult to see this area. For a positive diagnosis, a sample that includes the canker is necessary. Unfortunately, this isn't always possible since the canker may be in the trunk or large branches.
Prevention is generally easier than trying to deal with an infected tree. The best way to avoid canker diseases is to keep trees as stress free and healthy as possible. Promoting good air circulation by proper spacing, avoiding drought stress by watering when necessary, planting in appropriate sites, and mulching can help maintain tree vigor.
Once a tree is diagnosed with a fungal canker, all of the treatments above may aid in slowing disease progression. Pruning out infected branches should be done during dry weather. If the main trunk is infected, everything above the canker will probably die, since the fungus can eventually girdle the trunk, disrupting water flow.
Two of the most common canker diseases of conifers in Iowa are caused by the fungi Cytospora and Diplodia, also known as Sphaeropsis. To read more about these canker diseases and those of other trees, see the new ISU Extension bulletin, Fungal Cankers of Trees , SUL 11.
This article originally appeared in the October 12, 2001 issue, p. 113.