You’ve probably seen them – funny-looking brown balls stuck to eastern red cedar trees. Sometimes, the balls have long gooey orange tentacles hanging from them. Do you know the story behind them?
Cedar-apple rust is a fascinating organism that uses two different hosts to help it complete its life cycle. Galls that form on eastern red cedar trees eventually release spores, some of which make their way to leaves of apple or crabapple trees. On those leaves, they stimulate formation of yellow lesions that eventually mature and create more spores that then need to make their way back to another cedar tree to complete the cycle. The lesions on the leaves can be harmful to the apple trees (including the one in my yard) but I’m not sure there’s any big impact on cedars.
You can read much more about this at the Missouri Botanical Garden’s website.
I found the above gall at our family prairie last month. And yes, I did cut the cedar tree down after I photographed the gall (see photo evidence below).
The Prairie Ecologist 
Another good reason to keep cedars at bay – keep our apple trees healthy!
Hey Chris, really enjoy your blog even though I am not an ecologist by training. Just curious why you cut the tree. Was it to prevent the spread of cedar-apple rust? Is this not a natural host-parasite interaction (i.e. has the rust been imported from somewhere)? Thanks.
Hi Dylan, the cedars invade grasslands around here without fire to suppress them and without control they turn prairies into woodlands. (which is not what we want)
I remember seeing these galls on the cedars in my yard when I was a kid back in Virginia. I had no idea they were cedar apple rust. Thanks for the info!
Of course, I didn’t think about this when I plant my 7 apple trees. It’s a good way to see which variety is CR resistant.