If you failed to get rid of dead wood and clean up your landscape last fall, get it done now. You can refer to issue no. 19 of the 2001 Home, Yard, and Garden Pest Newsletter for details. Plant material infested with pathogens will soon begin to develop and spread further in the planting. For example, brown rot of ornamental fruit overwinters on rotted berries on the ground or in the tree. Removing these will greatly decrease disease incidence in 2002. Wood rot and root roots can invade woody plants via cankers. Don't delay in removing these where possible.
A canker is a dead area on the stem or trunk of a tree or shrub. The vascular tissue under the canker is dead as well. As the canker girdles the stem, leaves begin to wilt, turn yellow and then brown or black. With fire blight, this happens very quickly. Fungal cankers progress more slowly. Bark on the younger twigs may lose color or blacken, depending on the canker or plant involved. The cankers produced by fire blight are often black on pear and brown on apple. If a canker girdles the stem, the twig dies from that point to the tip.
When pruning out cankers, keep in mind that this wood is infected with a pathogen. Remove affected wood from the site. Disinfect pruning shears between cuts if possible. Always try to prune in dry weather to prevent pathogen spread. Refer to the fire blight article for particular exceptions for that disease. Oaks should be pruned in the dormant season. Sap flow in the growing season often attracts beetles that might bring the oak wilt fungus to the tree. A report on cankers and dieback diseases of trees is available as Report on Plant Disease, no. 636, available through Illinois Extension offices or on the Web at http://www.ag.uiuc.edu/~vista/horticul.htm.