Ash tree species are fast growing and provide a quick source of shade. They are relatively easy to grow in Illinois. For these reasons, you will find many ash trees in landscapes in Illinois. Most are in good health, but some have been plagued with problems, including ash yellows, ash decline, and Verticillium wilt. The problems, which can be found throughout Illinois, are discussed in detail in issue no. 7 of this newsletter.
Branch dieback and decline seems to be a symptom common to the diseases mentioned. All definitely cause plant stress. With stress comes the invasion of secondary canker fungi. If we are not willing to do a little helpful management, these cankers girdle and kill branches, allowing wood rot fungi to enter larger limbs and the trunk. The result may be a slow decline and death of the tree. Because ash trees grow quickly, they can overcome some of their problems with a little help from us.
Cankers are dead areas on the stem or trunk. These are fairly easy to spot on ash. Usually the wood is darkened and sunken or roughened. Fruiting bodies of a fungus are usually visible in the canker as small, pinhead-sized spots embedded in the bark. Such spotting is found on healthy wood. The cambium in the cankered area is dead, so peeling back the bark in this area reveals brown wood below. Remove all of the dead wood now. Cut until you leave only healthy wood on the branch. You may have to use some discretion when cankers occur on the trunk or large limbs but have not girdled the wood. Because canker fungi often enter a tree on old branch stubs, be sure to use sound pruning practices. Cut branches just outside the branch collar, not flush to the trunk. Remember that the wood that is cut off is infected with a pathogen, so remove it from the site. Only work on trees in dry weather to avoid spread of the fungi involved.
Canker fungi are stress pathogens. Assess the ash and the site to determine what stress may be contributing to decline. Often drought or flooding are factors in root injury leading to tree stress. Be especially diligent about watering ash trees in drought stress. Fertilize with a balanced tree fertilizer, but avoid excessive nitrogen fertilization. This species responds very well to water and fertilizer applications. For those of you with healthy ash trees, keep them healthy by watering in drought and removing dead wood as it appears. For information on canker and dieback dis-eases of woody plants consult Report on Plant Disease, no. 636, available on the Extension VISTA Web site.