Natural Object: Cedar-Apple Rust

Many of us look to the stars hoping for new discoveries. Obviously, there’s plenty to find out there. But some people seem to think everything has already been done right down here. Ha!

Last week I was on Nantucket Island, off the coast of Massachusetts. Thirty miles at sea, it’s a damp and very windy place. Evidently, this kind of climate is just about perfect for cedar-apple rust. This is a fungus, Gymnosporangium juniperi-virginianae, that has a fascinating, dual-tree life cycle.

The picture above is of the gall, which grows on Eastern red cedars (actually junipers, Juniperus virginiana). There seem to be a good number of them this year. For apple growers, the rust is a disease, hence it’s fecund representation on the web on ag and horticulture sites. For amateur naturalists, it’s simply mind-bending.

The “blooming” of the rust is a late April/early May event. I’ll be missing it this year, so the photos shared below come from my archives from several years back. (Pre-macro lens days.)

In summary, spring sees a gall, which has over-wintered on an eastern red cedar, bloom with these orange gelatinous tendrils, called telial horns, which send teliospores on the wind to find, hopefully for the fungus, apple trees. (The nearest apple tree I know of to these cedars is about a football field away.) There, on the apple’s leaves, fruits, and stems, the rust grow through the summer. Then it too “blooms,” from colorful lesions, but very different looking. These send other spores out to infect the nearby red cedars for the over-wintering … and around it goes.

UPDATE: Some photos of this lifeform from 2011.

10 Responses to “Natural Object: Cedar-Apple Rust”


  1. 1 Amy Melson April 15, 2010 at 9:19 am

    That’s got to be a cure for something.

  2. 3 mthew May 2, 2010 at 6:26 pm

    It may already have, judging from some of the pod-people in charge of things.

  3. 4 suzi smith May 3, 2010 at 3:48 pm

    that is fascinating!

  4. 5 joan knapp May 3, 2010 at 9:00 pm

    We’ve had a couple of ’round’ of them this year. They are fascinating and a little disconcerting – apart from their agricultural importance. Thanks for sharing.

  5. 6 Joy K. May 18, 2010 at 7:48 am

    I just found one in a juniper tree along my driveway! Thanks to your post, I knew what it was.

  6. 7 Sylvia Lail May 1, 2016 at 3:08 pm

    i found two of my cedar trees loaded today with these orange, gangling looking telial horns. I have been in this home for 25 years and this is the first time to see these. I have two apple trees across the yard from the cedars.


  1. 1 Natural Object: Cedar-Apple Rust « Backyard and Beyond Tree Me Trackback on April 15, 2010 at 2:16 pm
  2. 2 Cedar-Apple Rust « Backyard and Beyond Trackback on June 1, 2011 at 8:02 am
  3. 3 Rust Never Sleeps | Backyard and Beyond Trackback on May 19, 2018 at 8:01 am

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