Mystery Photo – Apple Cedar Rust Gall
Mystery Photo: Cedar Apple Rust
David Fontaine, of Ferrisburgh, Vermont, submitted a mystery photo of a cedar-apple
rust gall that overwinters on cedar trees and is caused by a fungus which
requires two hosts, eastern red cedar and apple trees, to complete its life
cycle. When the galls get wet from spring rains, orange, spore-filled fingers or horns, called telia, emerge from pores in the gall. As the horns absorb water, they become jelly-like and swollen. When
the jelly dries, the spores are carried by the wind to apple trees, where they
cause a brownish mottling on apples, referred to as cedar apple rust, which
makes apples difficult for growers to sell, even though it doesn’t affect the
flavor or texture of infected apples. The rust produces spores on the underside of apple leaves in late summer,which, if they land on eastern red cedar trees, cause galls to form, thereby continuing the cycle. Spores produced on apple do not infect apple, only cedar; spores produced on cedar infect only apple.
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