Terrible orange scum on my cedar tree

Asked April 25, 2018, 7:19 PM EDT

I just discovered a disgusting orange scum growing on my cedar tree that looked healthy until this past week. Can you identify what looks like fish roe growing on my tree? See photos attached. Sandy McGraw 2965 St. Peters Church Road, Waldorf, Maryland 20601 301-645-2973 sandymcgraw@comcast.net

Charles County Maryland fungus cedar apple rust tree diseases

1 Response

Good Morning!


This is cedar apple/pear/quince rust (a Gymnosporangium rust disease) and is very common on cedar in the springtime. Members of the genus Juniperus (like Eastern red cedar and juniper) are a host of one of the life stages, like you are seeing now. The fungus doesn't really cause harm to cedars, but the spores from this stage are spread to apple, pear, quince, hawthorn, and related species where they can damage leaves and fruit. It is possible to prune out the fungus on the branches, but on large trees there would almost certainly be infections on areas that are out of reach for pruners. There is no practical way to manage it with chemicals. The best way to manage this disease is to plant varieties of apple, hawthorn, pear, ect that are resistant to rust. Again, this will not damage the cedar.

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