Tag Archives: cedar-apple rust

Gymnosporangium juniperi-virginianae

Garden of Horrors: Gymnosporangium Juniperi-Virginianae

The natural world is often stranger than we give it credit, case in point heteroecious rust fungi which requires two hosts to complete their lifecycle. And some choose to do it in the creepiest way possible.

Enter Gymnosporangium juniperi-virginianae more commonly known as cedar-apple rust. The only thing more disturbing than its letter-salad binomial name is the way it looks—in particular in the spring when the pathogen is ready to leave its cedar/juniper home and find its next host.

The gall of Gymnosporangium juniperi-virginianae with with telial horns
The gall of Gymnosporangium juniperi-virginianae with telial horns

See what I mean? There’s something downright disgusting in those creepy finger-like protrusions. They remind me of an inverted tree-anemone (a comparison that is even more accurate when they’re wet.) Those are called telial horns, and they sprout from galls created by the fungus from the year before. Once it warms up the galls “sprout” and begins spreading spores that are usually looking for apple trees, although it’ll happily infest pears or hawthorns as well.

It’s not kind to the fruit trees either. Infestations can reduce the yield on crops and cause blemishes in the fruit—they can also kill the cedar trees as well. It’s so widespread that there’s loads of information out there focused on prevention. Luckily, the Teliospores can’t travel too far. So the best way to control the fungus is to remove cedars found within a mile of orchards. No cedars no fungus.

Here’s a quick video from Cornell University showing a timelapse of the horns growing from the fungi galls over six days. Vermiphobes you might want to look away.

Happy gardening.


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