Cedar Rust suspected on Hawthorne Trees
I have planted two 'Winter King' Hawthorne trees for landscaping and wildlife purposes in December 2019 (which was a mild, warm winter). The trees are about 15' tall and maybe 10 years old. I did not realize a nearby cedar tree could cause a fungus problem to occur on them. The Hawthorne trees have bloomed this spring and are growing fruit but the fruit are showing what I suspect is cedar rust (please see image). What can I do? + cut off the infected berries? + cut down the cedar (it's about 10' and 25 years old) + spray a fungicide on the hawthornes (which one will work effectively at this stage of the disease? will this harm birds and bees?) + spray the cedar?
Thank you for your question. Your leaves and fruit are infected with a rust disease (cedar-apple rust or cedar-hawthorn rust). You may see a fair amount of leaf drop this spring. Rake up and dispose of as many infected leaves as possible to reduce the amount of innoculum available to infect the alternate host- Eastern red cedar. Weather is a large factor determining the severity of the disease year-to-year. Repeated severe infections can weaken the tree and cause dieback.
You can find additional information on our website. https://extension.umd.edu/hgic/topics/rust-diseases-trees
You could remove the nearby Eastern red cedar to reduce or eliminate the alternate host for the spread of the disease. The disease is more of a cosmetic issue with your hawthorn and not life-threatening. Sprays aren't typically recommended and they aren't effective at this stage of the infection anyway. Just rake up and dispose of the leaves and fruit that are showing symptoms.