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Synonyms and common names

Juniper-apple or cedar-apple rust
Juniper-hawthorn rust

This is a fungus which infects alternately members of the genus Juniperus and members of the subfamily Maloideae. Because of it, apple and pear growers may have to remove any Junipers in the area. Note that the common name 'cedar-apple' rust is a mis-nomer based on the mis-application of the name 'cedar' to some junipers; cedars are immune.

In Juniperus, the fungus forms a ball about 3 cm in diameter which produces a set of orange tentacles. These are the spore tubes. The spores are released and travel on the wind until they hit an apple, pear, or hawthorn tree.

On the pear tree, the fungus produces yellowish depressions on the leaves. It also infects the fruit, which grows whitish tubes like snakes on Medusa. These are the spore tubes. The spores must then go to a juniper to complete the life cycle.