Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Earth replenishing rainfall brings out the best in plants and animals of spring. Forest goers have been busily searching for morels and other interesting fungi that have been showing their colorful faces. When it comes to fungi, sometimes I wonder, who needs science fiction in the home theatre when you can have really “gross-out” fungi that occur naturally in the home landscape?
Cedar-apple rust is just one of those cool fungi. Caused by the fungus Gymnosporangium, it rarely causes significant damage to the junipers (Cedar) that it resides on for half of its life. According to Jan Byrne, plant pathologist for MSU Diagnostic Services, the weather we have been experiencing is just right for this science fiction fungus to show up. This past week, orange, gelatinous, tentacle-like projections can be readily seen on cedars that may cause you to think that someone had decorated them for Christmas. With the right amount of rainfall, the woody galls “bloom” into action.
Known as a teliogall, it is even more interesting to touch. I know, as the mother of a nine-year-old, something that replicates gooze, silly putty or other slimy substances is the best entertainment that the outdoors can provide.
Jekyll and Hyde
From a science perspective, some rust fungi lead interesting lives. This pathogen alternates between two hosts according to Byrne. The big, orange “Jello fingers” produced on the cedar in May give rise to tiny spores that are carried by wind to the alternate host – an apple or hawthorn. The gall on the cedar will quickly dry up and hang on the tree for several years.
Although this disease does not threaten the health of the cedar, it can prematurely defoliate non-resistant apples, crabapples and hawthorn later this summer. Leaves will first show a classic spot that typically is bright orange to yellow with a lighter outer ring. The underside of the leaf may show light colored, cup-shaped structures. Fruit also can be disfigured.
For the most part, this disease is more of an interesting lesson for a fourth grader than a threat to either plant. However, in some instances, it does warrant a control strategy. If you have a valued hawthorn or crabapple, removal of the alternate host (cedar) that is in close proximity may be an option. Because fungicides will not control the “blooming” gelatinous galls, a more likely solution, according to Byrne, is to prune out the galls in the cedar this fall to avoid infection next spring. Fungicides are an option for highly valued plants or for fruit production.
Most landscape junipers show a fair amount of genetic resistance. The most affected plants are the Eastern red cedars that grow prolifically along the road side. When using hawthorn or crabapple in new landscapes, take note if there is a large population of wild cedars in nearby areas. For a list of resistant plants contact the Kent/MSU Extension office, Lawn and Garden Helpline at 616-336-3881.