Fungal Orange. Pear Rust, Gymnosporangium sabinae, on Juniperus sabina, Savin Juniper, Hortus Botanicus, Amsterdam, The Netherlands

Tom Buys, one of the highly knowledgeable gardeners of the Hortus Botanicus, this morning took me around to the evergreen section to show me this Pear Rust. In the gloomy days and the shade I hadn't noticed it before and he himself had only just discovered it too. In fact, on the way over we stopped by a Pear Tree, not a hundred metres away to see if its leaves might have been infected. But no(t yet), it seems.

This fungus or rust is here thriving - already a bit dessicated - on Juniperus sabina, Savin Juniper. Juniper is its winter host, and Pear its Summer home. After a wet spell, the spores in the bark of the Juniper will grow out to these orange nodes and they in turn will release spores which will settle on Pear leaves as their secondary host. In fact, those spores are not able to reinfect our Juniper and need to cross over into the world of a Pear Orchard for continued life.

Done