Cedar-apple rust

Extension agents probably hear it a lot this time of year: What the heck is that alien orange thingy in my cedar tree?!



Check out those gelatinous telial spore horns (noodly appendages).

It's Cedar-apple rust, and it's caused by the fungus Gymnosporangium juniperi-virginianae.

If yours doesn't look quite like this, it might be one of the similar (related) rusts: Cedar-hawthorne rust or Cedar-quince rust. Check the chart of rust differences.

Basically, the Cedar-hawthorne rust's noodly appendages are short and stubby (as opposed to the long and thin ones on the Cedar-apple rust gall shown here). And Cedar-quince rust is mainly just orange goo on bark and twigs. You can see pictures of the latter on my previous posts on the subject here and here. The photos at the first link also show how the rusts appear when they're not quite so wet.

I can't seem to stop writing about these rusts when they make themselves so obvious in the spring. The way they alternate hosts, and of course their appearance, is so unusual.

Fungi expert Tom Volk has written about Gymnosporangium juniperi-virginianae too, in a much more scientific fashion, here.