This time of year is a great time to talk about one of the major diseases that affects our area on a popular ornamental tree. Golden canker, officially known as Cryptodiaporthe canker, is a fungal infection of alternate leaved dogwoods, also known as pagoda dogwoods. It’s caused by the fungus Cryptodiaporthe corni . Initially the fungus survives within the plant as an “endophyte” which is a small organism that lives within a plant without causing harm. It’s unknow how or why this fungus switches to an infectious version that harms the plant. This infection can kill the host plant if it reaches the main trunk of the plant and should be taken seriously. Like the name suggests this fungus will turn parts of the branches of the affected tree gold to tan in color. This mainly shows its effects at the tips of branches of the tree but it can be hard to see during the growing season, which is why now in the dormant part of the year is the best time to look for signs of this disease.
Within the golden portions of the branches, small, orange dots will begin to appear in these areas. These orange spots are actually the fruiting bodies of the fungus, meaning the structures of the fungus that emit spores that can be spread to other parts of the same plant or to a new plant host, though the exact method it infects plants by is unknown. Humid conditions encourage the spread of the disease. The golden portions are dead wood and will not leaf out, but the infection goes further beyond the visibly infected sections.
The only way to treat, and save, a pagoda dogwood infected by golden canker is through pruning. No fungicides are effective as treatment as the fungus lives inside the branch. To effectively remove diseased portions make the pruning cut about six inches below the visible infection, just above a live bud. Between each cut you should disinfect your pruners using either 10% bleach solution for about 30 seconds or 70% rubbing alcohol. This will help prevent the spread of the fungus to uninfected portions of the plant. Pruned off portions should be disposed of by either burning or burying.
It’s also important to note that this disease affects specimens regardless of soil type or if it is planted in more sun or more shade. To try to avoid this fungus in the future you should try to reduce the tree’s stress by properly siting new specimens and watering as needed.
References
UW Extension: https://hort.extension.wisc.edu/articles/golden-canker-cryptodiaporthe-canker/
University of Minnesota Extension: https://extension.umn.edu/plant-diseases/golden-canker-pagoda-dogwood
